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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds .
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if solids are supposed to be denser than the liquids of the same substance , how come ice floats on water ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down .
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where does the energy go to ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule .
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is this process suppose to be showing the process of a solid turning into a gas ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ?
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are the words underneath it that are flowing with the arrow are these essentially steps like step 1 , step 2 , step 3.. ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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or a gas . so let 's just draw a water molecule . so you have oxygen there .
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why do the h atoms go lower than the o atom in a water molecule ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy .
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is this because o is `` hogging '' the electrons more than the h ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q .
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what are the two factors responsible for interconversion of matter ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there .
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what is the little `` s '' looking symbol that sal drew to demonstrate a positive or negative charge ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other .
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so my question is this what does the photons do with the electrons in the hydrogen molecule to make the molecule move faster ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth .
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why is iodine sublimation done in a fume cupboard ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ?
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at 17 , the property of matter only depends on the temperature ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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let 's say that 's that line . what happens to a solid ? well , it turns into a liquid .
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what is kelvin ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil .
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what happens to the particles in sublimation ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line .
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makes me wonder , though - how exactly do wet objects become dry ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens .
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does the water actually vaporize into gas form ( which i 'd doubt , as it certainly does not seem like the appropriate temperature is reached ) ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth .
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what are the properties and limits of bec and plasma ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense .
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according to the graph the temperature of a solid is positive , but should n't it be negative since it freezes ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth .
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what is the fifth element ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here .
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but does n't our blood contain plasma , and is n't our average temperature is 37c ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o .
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when that graph has been plot , ( melting ice ) how come after showing the increase in temperature , reaching 0 degree celsius , sal says there is no change now ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth .
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what 's a bose-einstein condensate ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content .
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is enthalpy like conducting heat ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether .
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how does that idea fit with the idea of the added heat increasing the pe of the molecules during phase changes ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that .
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0 is there a name for this little period where the temperature stays constant although we are adding or removing a certain amount of heat ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule .
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i know there are 4 main states ( solid , liquid , gas , plasma ) but i 've heard of this 5th one called bose-einstein condensate.what is it ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature .
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we know that there is a limit to how much energy you can take from a particle ( 0 kelvin ) , but is there a limit to how much energy you can put into a particle ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats .
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are there any liquids besides water that become less dense when they become solid ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other .
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what does higher energy state mean ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid .
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how liquid crystal works as a temperature sensor ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth .
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what is a dipolar bond ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here .
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what happens if the kinetic energy of the composite particles increases ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen .
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how many electrons are there in a hydrogen atom ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure .
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to about i really do n't understand what polar bonds are exactly so what are they ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas .
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what is the fourth possible state of matter at very high temperatures sal mentions at the beginning ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule .
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if oxygen is a gas and has a very high energy level , why does it not feel hot ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ?
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what is an example of something that is not a solid liquid or gas ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas .
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is plasma the fourth matter ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up .
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after 1 is there such a thing that if you add more heat , the kinetic energy is so high that bonds of h and o start to break up and atoms of h and o start to move away and being independent elements ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds .
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so i was wondering what happens if i put water at 0 `c and keep the temperature constant ... will it turn into ice and then into water , and then into ice , ind then into water and so on for ever ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple .
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what state are atoms in ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy .
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when sal says that water and steam can be at the same heat , it makes me wonder what stimulates the change is it consistency of temperature or something more complex like quantum fluctuations ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds .
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at about 1 what are the periods in which the temperature does not increase called ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees .
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do non-newtonian fluids take shape only when pressure is applied ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content .
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what is hardness and how is it related to density ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat .
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at 1roughly , how does superchilled water fit into this diagram ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine .
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how exactly does evaporation work ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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let 's say that 's that line . what happens to a solid ? well , it turns into a liquid .
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what happens during sublimation ( solid to gas ) and deposition ( gas to solid ) , in terms of kinetic energy ( heat ) ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state .
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how do the molecules skip the liquid state and go directly to the gas state ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule .
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what are the various gas laws ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat .
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can we substitute 'time ' for 'heat ' in the temperature.vs.heat graph ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state .
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if solid things are supposedly colder , why do i feel warmer when i 'm lying down on the floor rather than in a pool ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy .
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can anybody explain the various energy changes taking place ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy .
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during the phase change all the heat energy is converted only into potential energy and there is no increase in kinetic energy ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple .
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liquid state will have have both kinetic and potential energy more than that of solid state ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here .
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how will the average kinetic energy be low even if each molecule has high kinetic energy ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster .
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why are ranges used when dealing with specific heat of steel and brass ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o .
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how is it possible that the same temperature is required to melt the ice and then freeze it back ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ?
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does the speed of vibration in the molecules increase the vibration does ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ?
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what is the nature of heat such that it imparts additional momentum to molecules ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure .
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what is the mechanism of heat transfer that makes molecules move ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth .
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waiiiiittttt ... what about plasma and bose enstein condensate ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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or a gas . so let 's just draw a water molecule . so you have oxygen there .
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is a molecule bigger than an atom ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy .
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oxigen is made out of what ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid .
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why the volume of liquid is higher than the volume of solid ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy .
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is a black hole made out of matter ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line .
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what gives waves it curvy shape ( sea wave ) ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens .
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is there a fifth state of matter ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens .
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if sand is solid , how does it flow ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy .
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can anyone tell me why there is no rise in temperature of a substance when it undergoes a change of state although it is still being heated ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up .
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is the heat of vapor like that too or are they both just for the water molecules ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here .
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so , my question is that- if they move around so much then definitely the energy would have been used , so there will be a time when all the kinetic energy will be used up in you know moving around so why do n't the gases convert into liquid after losing kinetic energy ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating .
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what would make a molecule electronegative ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule .
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quick question : can we capture gas and heat it more ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is .
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when it was i was wondering how many atoms does liquid have ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy .
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when a solid changes to a liquid , does its mass change ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then .
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is n't heat and temperature the same thing ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule .
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what is the word when you turn gas into another state ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q .
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so if there is the states of matter then what type of matter is dark matter ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil .
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what happens when a gas gets really hot ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy .
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what is the relationship between entropy and internal energy ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule .
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but what are atoms - are they solid , liquid , gas , or something else ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with .
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for the temperature to increase beyond 100 degrees celsius , would n't you need a closed container to allow the pressure to increase ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure .
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and now i 'm confused , which bonds are breaking and what bonds are where ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in .
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what does the heat of fusion mean in the video ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth .
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how cold is bose-einstein condensates ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q .
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how are the states of matter related ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens .
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what state of matter is slime ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would .
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is it possible that in order to be invisible , all you have to do is separate your molecules farther apart ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens .
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what is the forth state of matter , called plasma ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period .
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why does n't the temperature go up ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens .
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is n't matter made up of solid liquid , gas , and plasma ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o .
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what was the begginning part about hydrogen and heat and ice ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q .
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what are the seven states of matter ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule .
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sublimation is when you go straight from solid to gas , right ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q .
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are n't there 5 states of matter ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule .
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1.solid 2.liquid 3.gas 4.plasma 5.bose-einstein what about them ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down .
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where does the energy go ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma .
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why is n't fusion used to generate electricity ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active .
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why exactly is this , is there something specific that happens on a molecular level ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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at 1did sal mean 0 celsius water or 0 celsius ice ?
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