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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 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 .
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why did n't the temperature ever get higher than boiling point ?
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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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at around how can a molecule have partial 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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what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens .
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why is water so special ?
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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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why does it have special characteristics such as ice floating on liquid 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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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 .
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and why can all three states of water coexist with one another in the same environment ?
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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 about plasma and 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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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 light a 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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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 .
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what are valence pairs of electrons in an molecule of oxygen ?
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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 about dry ice does that change the temperture too ?
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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 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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6 , what is the fourth state of matter sal refers 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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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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4 the bonds between the molecules are described as polar but what does polar 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 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 other two states ( plasmas and 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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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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no doubt rubberband is a solid but we can stretch it 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 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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does bose-einstein condensate ( bes ) count as a 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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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 are covalent bonds created between hydrogen and oxygen atoms anyway ?
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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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would they form bonds if individual atoms of h and o were put into a container , just like that ?
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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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what happens when you approach the freezing temperature of something ?
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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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can you heat up a rock so hot to make it 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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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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why do temperature increases when kinetic energy 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 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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what exactly is potential energy in terms of molecules and changing 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 is the difference between vapour and 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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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 .
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if you keep adding heat to the vapor stage in which the molecules are separated , will the bonds between atoms break to individual h2 and o ?
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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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what is the temperature of room temperature water after salt is added to 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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let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept .
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what does that weird symbol sal used ?
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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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when the water frozes , what actually takes the energy of 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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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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if molecules stick together because of this small electrical charge then why if i break apart a solid into 2 halfs wont the halfs reattach to each other if i place them next to each other again ?
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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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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 .
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your explaination hinges on the attraction between water molecules that have this charge separation , but how about other liquids that do n't ?
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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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why would liquid nitrogen for example stay a liquid under the right pressure and temperature when n2 is more or less electrically neutral ?
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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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do the polar bonds cause water to follow other water particles ?
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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 frost considered 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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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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does during change of states electrons get excited too ?
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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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can someone please explain this to me , as well as how this happens at 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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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 # fire # 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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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 is the symbol sal draws ?
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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 technically possible , what would a 0 k `` solid '' /be condensate be 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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force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy .
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on a similar note , how cold does a be ( bose-einstein ) condensate have to be to be called so ?
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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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all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is .
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could you theoretically melt a rock ?
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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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ok so if you are cooking and you are boiling water there is really a range of temperatures that will give you a rolling boil that is at a constant temperature even though you could go between a range of temperatures being 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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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 heating a solid have these steps , then how does it change to 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 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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is n't density an intensive property ?
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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 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 .
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what i dont get is that oxygen is a form of gas , correct ?
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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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well when you are exhaling when you are breathing its carbon monoxide or dioxide , 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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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 .
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the order of potential energies for substances goes gas = highest potential energy liquid = middle potential energy solid = lowest potential 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 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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should n't there be 2 partial negative charges on the oxygen atom in 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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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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if you are in a higher energy state does it means like he said when you are going up the potential energy grows b/c u r going up but the energy goes higher because the gravity is pulling u down ?
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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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in term of charles 's law explain why -273*c is the lowest possible 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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well , it 's joules . force times distance . but anyway , that 's a side-note .
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does the salt particle occupy the space due to force of attraction from the water 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 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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why liquid does not obey boyle 's law ?
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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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what is the difference between an atom and a 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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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 .
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the amount of matter in a given space ; the relationship between a substance mass and its volume is known as ?
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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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why does the ice turn 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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what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens .
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what about auto-ionization of 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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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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why is it called heat of fusion if its not fusing two things together rather its drawing two things away ?
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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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can we add latent heat concept also with this topic explained in the phase 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 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 many kinds of matter are there and what are they 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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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 characteristics 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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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 .
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how can a triple point ever be 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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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 .
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i could see a point between solid and liquid , and liquid and gas being possible , but how could there ever be the appropriate conditions for the solid form and the gaseous form of the same substance to exist simultaneously ?
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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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why does water expand when it freezes instead of contracting ?
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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 . because that 's what it is .
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you said a rock is solid magma ... is n't that only ingenuous rocks ?
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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 that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid .
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why does n't the temperature 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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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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is anti-matter a type 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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what state of matter is toothpaste 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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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 cream is an one of the 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 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 do gas and solid have in common ?
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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 type of matter is shaving cream ?
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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 many states of matter are there ?
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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 's the fourth state of matter and how high does the temperature have to be to reach 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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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 .
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how and why pressure affects melting point and boiling point ?
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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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at what are the three main 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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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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what are polar bonds ?
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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 bose einstine 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 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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my question is that since energy can not be created nor destroyed , where does it 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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if solids have a very high amount of attraction forces between their particles , then why the why do n't two broken pieces of a wooden plank attract each other ?
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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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why then is solid ice less dense than liquid 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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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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also , if you have a graph similar to the one sal drew , should n't there be a `` jump '' in the graph when the ice in this case has fully melted because of all of the accumulated 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 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 plasma considered a 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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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 .
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would n't the bar be going up at a slight angle ?
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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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you say the ice melts in that period , so why dosent the bar go up very slightly ?
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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 , 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 .
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then how come the vacuum between these molecules of air does n't affect the molecules themselves ?
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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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why do only some things melt ?
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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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would plasma be considered a 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 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 .
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wait , why is oxygen more electronegative than hydrogen ?
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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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why is oxygen not hot if its not 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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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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how much hot steam can get ?
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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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so for every substance , not just water , does it take energy to change states ?
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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 many states of matter are there ?
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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 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 .
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is the phase diagram supposed to be continuous ?
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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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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 .
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there are discontinuities at the boiling and freezing points , but did khan put those there for simplicity ?
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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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is there any difference in the lenght of 20 meter steel girder when standing vertically and horizontally ?
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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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how do non-newtonian substances like baking soda and water change their state of matter without heat being supplied ?
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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 ? because the molecules are much further apart .
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why is it that we can see solids and liquids but not 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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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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so anything above 100 degrees is the boiling point and anything below 0 degrees is the freezing point ?
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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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how do solids get a proper shape ?
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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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what causes so much pressure that the molecules in the solid do n't tear of so easily ?
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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 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 .
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how come the molecules do n't fall off on their own ?
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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 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 .
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ay why does n't it change 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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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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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 ?
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what could be the 4th 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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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 .
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7 he was talking about how the temperature stays the same for a short amount of time ... can someone explain that to me ?
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