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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 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 .
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do you have types of measurements for water like the i think the si or the is units and if you do can u tell me were they are at ?
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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 is the plasma state 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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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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1 , 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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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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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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at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content .
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what 's the difference between enthalpy , heat and 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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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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are there only three states of matter ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and 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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in the video why is it that there are only 3 states mentioned ?
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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 does latostructure 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 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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which matter do the molecules r mor seperated ; liquid or solid ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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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 is polar and non polar bonds that sal mentions 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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well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o .
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khan can you please tell me , where does plasma goes between these three states and without of any raise in temperature , how dry ice produces 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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we 're still a solid . and then , we finally turn into a liquid . let 's say right there .
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what happens to the 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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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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rock can be considered as solid magma , but then what about diamond ?
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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 . 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 .
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how can hydrogen and oxygen obtained from 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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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 there is no fifth state of matter , then what is bose einstein condensate ( bec ) ?
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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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why are the states of matter so clearly defined ?
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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 is there not , say , a `` solid-liquid '' structure between the formation of ice and liquid water if the state is only defined by the presence of intermolecular forces and kinetic energy ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating .
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would then be time for london dispersion forces to shine or would it not become solid or something else ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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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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i know there is something called bose-einstein condensate , but what is it ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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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 will happen when a gas is continuouly heated.after molecules of gas have maximum intermolecular space they can attain ?
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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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is the state of mater ( liquid ) polar or bi- polar ?
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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 , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other .
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what is a lattice structure ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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you can also have 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 .
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if we take a cloth which is completely wet in zero gravity and spin over there will the water fall 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 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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how does sublimation ( transformation from a solid to a gas ) work ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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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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i have a dought on plasma [ 4 rth state of matter ] what does it do ?
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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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how to identify 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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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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i really do n't understand the factors affecting the solubility especially the micelles ... is there any video for the description ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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it '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 .
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can someone tell me the difference between diffusion and brownian motion ?
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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 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 .
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what are partial negatives and positives ?
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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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how is liquid more dense than 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 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 gas and vapour ?
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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 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 .
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how can you add heath without raising tempeture ?
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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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why does the temperature stay the same during a phase 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 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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why in sublimation the solid do not convert into liquids ?
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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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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 .
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if all molecules are vibrating and moving , then what fills the space where the molecules are not ?
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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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can somebody explain to me what plasma is exactly ?
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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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the five states of matter of plasma , boze einstein , liquids , gases , and solids , 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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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 do ice sublimate to gas when heated in vacuum ?
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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 bose-einstein condensate 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 when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy .
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sal made a mention of a 'latostructure ' can anybody explain 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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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 .
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can hot temps melt rocks 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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the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds .
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if ice is a solid , and water is a liquid , how come ice still floats on water ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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or a gas . so let 's just draw a water molecule . so you have oxygen there .
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is it possible to vibrate a water molecule loose without heating it up ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens .
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is a bose-einstein condensate also 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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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 .
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what happens when the steam gets hotter and hotter ?
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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 i were to freeze gas what would happened inside the molecules and substances ?
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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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so if bromine reaches its melting point , what happens ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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we 're still a solid . and then , we finally turn into a liquid . let 's say right there .
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since anything can be turned into a solid , liquid , or gas by adding or removing heat , why does n't burning wood turn into a liquid ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat .
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would atm be equivalent to heat ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule .
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about phase transitions , do all materials and elements follow the same rule of giving more heat changes into 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 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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how does a phase change graph differ from a cooling curve ?
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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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do all the hydrogen bonds break from the heat of fusion ?
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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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in a compound like water will the oxygen always have a partial negative ?
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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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do hydrogen bonding and dipole forces play role in the anomalous behavior 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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that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating .
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what would happen if we boil blood ?
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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 the heat of vapourisation greater than the heat of fusion ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content .
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can anyone explain me the term enthalpy ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma .
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why are liquids termed as in-compressible and solids as not-compressible ?
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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 , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other .
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what is a `` lattice structure '' ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there .
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what does it mean to say that a positive charge is surrounded and held by a sea of electrons ?
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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 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 .
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why do solutions showing positive deviation from raoult 's law have enthalapy as endothermic ?
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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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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 .
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what is the s symbol that sal drew ?
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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 happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line .
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is plasma also present in earth ?
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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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during gaseous mode when molecules completely separate from each other , we could say that the distance from one molecule to another reduces electronegativity ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat .
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is heat attracted to coldness ?
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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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if there is 4 states of matter , how come we are n't learning about plasma ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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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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why does liquid change to steam ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple .
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what type of state is glass ?
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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 use magenta . so as i add heat , my temperature will go up . heat is a form of energy .
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how is heat different from 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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i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil .
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what happens when you continually add heat to 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 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 a sooty flame contains gases and tiny solid paricles ?
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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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1so , when you go high enough , does it stop getting hotter as gas turns to plasma ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and 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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how many states of matter are there altogether other than solid , liquid 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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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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5 , sal says `` the change in enthalpy is the change in heat content '' is n't 'enthalpy ' : the energy that is stored in 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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at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat .
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so why would enthalpy be refered to as 'heat content ' ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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then , 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 .
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when sal refers to 'pulling the molecules apart to give them potential energy ' , is he basically referring to translational energy ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here .
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when the temperature does not rise , does the heat convert into translational instead of kinetic energy ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens .
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why the is structure of water not linear but bent ?
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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 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 .
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how is oxygen more electro negitive 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 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 fire ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds .
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why volume of ice is more than that of water even though it is a solid ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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so 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 .
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when sal said the oxygen atom tends to 'hog ' the electrons , it that because it has a larger mass 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 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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just before few weak in news there was 6th state of matter 1 ) solid 2 ) liquid 3 ) gas 4 ) plasma 5 ) bose-einstein condensate 6 ) ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens .
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is there 6th -7th state of matter exists ?
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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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at 10 : is it possible to have < 0 degree c liquid water or > 100 degree c 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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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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i wonder what state is a black hole 's 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 what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other .
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what element is easiest to get to a plasma state and how much energy does it take ?
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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 does sal mean when he says '' molecules themselves are polar '' ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds .
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why the density of ice is less than water even the molecules of water are far apart than ice ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and 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 .
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is it possible to turn a gas straight into a solid without it turning into a liquid ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens .
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what is state of a matter of fire ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple .
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how do u determine the state of a molecular compound in reactions ?
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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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if the heat is provided the force of attraction between molecules remains unaffected so why do the particles in liquid and gases repel 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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at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat .
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when someone heat a piece of wood in a room which does't have air , what will happen ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma .
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why do only some solids like napthalene , iodine etc sublime ?
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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 is the density 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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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 .
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what r miscible and immiscible liquids ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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you can 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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1.09 : is n't steam actually a liquid ?
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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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when a water molecule is connecting to another water molecule , how can the hydrogen atom connect to two oxygen atoms , as it already has a full shell of two when covalently bonding with the first oxygen atom ?
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i think we 're all reasonably familiar with the three states of matter in our everyday world . at very high temperatures you get a fourth . but the three ones that we normally deal with are , things could be a solid , a liquid , or it could be a gas . and we have this general notion , and i think water is the example that always comes to at least my mind . is that solid happens when things are colder , relatively colder . and then as you warm up , you go into a liquid state . and as your warm up even more you go into a gaseous state . so you go from colder to hotter . and in the case of water , when you 're a solid , you 're ice . when you 're a liquid , some people would call ice water , but let 's call it liquid water . i think we know what that is . and then when it 's in the gas state , you 're essentially vapor or steam . so let 's think a little bit about what , at least in the case of water , and the analogy will extend to other types of molecules . but what is it about water that makes it solid , and when it 's colder , what allows it to be liquid . and i 'll be frank , liquids are kind of fascinating because you can never nail them down , i guess is the best way to view them . or a gas . so let 's just draw a water molecule . so you have oxygen there . you have some bonds to hydrogen . and then you have two extra pairs of valence electrons in the oxygen . and a couple of videos ago , we said oxygen is a lot more electronegative than the hydrogen . it likes to hog the electrons . so even though this shows that they 're sharing electrons here and here . at both sides of those lines , you can kind of view that hydrogen is contributing an electron and oxygen is contributing an electron on both sides of that line . but we know because of the electronegativity , or the relative electronegativity of oxygen , that it 's hogging these electrons . and so the electrons spend a lot more time around the oxygen than they do around the hydrogen . and what that results is that on the oxygen side of the molecule , you end up with a partial negative charge . and we talked about that a little bit . and on the hydrogen side of the molecules , you end up with a slightly positive charge . now , if these molecules have very little kinetic energy , they 're not moving around a whole lot , then the positive sides of the hydrogens are very attracted to the negative sides of oxygen in other molecules . let me draw some more molecules . when we talk about the whole state of the whole matter , we actually think about how the molecules are interacting with each other . not just how the atoms are interacting with each other within a molecule . i just drew one oxygen , let me copy and paste that . but i could do multiple oxygens . and let 's say that that hydrogen is going to want to be near this oxygen . because this has partial negative charge , this has a partial positive charge . and then i could do another one right there . and then maybe we 'll have , and just to make the point clear , you have two hydrogens here , maybe an oxygen wants to hang out there . so maybe you have an oxygen that wants to be here because it 's got its partial negative here . and it 's connected to two hydrogens right there that have their partial positives . but you can kind of see a lattice structure . let me draw these bonds , these polar bonds that start forming between the particles . these bonds , they 're called polar bonds because the molecules themselves are polar . and you can see it forms this lattice structure . and if each of these molecules do n't have a lot of kinetic energy . or we could say the average kinetic energy of this matter is fairly low . and what do we know is average kinetic energy ? well , that 's temperature . then this lattice structure will be solid . these molecules will not move relative to each other . i could draw a gazillion more , but i think you get the point that we 're forming this kind of fixed structure . and while we 're in the solid state , as we add kinetic energy , as we add heat , what it does to molecules is , it just makes them vibrate around a little bit . if i was a cartoonist , they way you 'd draw a vibration is to put quotation marks there . that 's not very scientific . but they would vibrate around , they would buzz around a little bit . i 'm drawing arrows to show that they are vibrating . it does n't have to be just left-right it could be up-down . but as you add more and more heat in a solid , these molecules are going to keep their structure . so they 're not going to move around relative to each other . but they will convert that heat , and heat is just a form of energy , into kinetic energy which is expressed as the vibration of these molecules . now , if you make these molecules start to vibrate enough , and if you put enough kinetic energy into these molecules , what do you think is going to happen ? well this guy is vibrating pretty hard , and he 's vibrating harder and harder as you add more and more heat . this guy is doing the same thing . at some point , these polar bonds that they have to each other are going to start not being strong enough to contain the vibrations . and once that happens , the molecules -- let me draw a couple more . once that happens , the molecules are going to start moving past each other . so now all of a sudden , the molecule will start shifting . but they 're still attracted . maybe this side is moving here , that 's moving there . you have other molecules moving around that way . but they 're still attracted to each other . even though we 've gotten the kinetic energy to the point that the vibrations can kind of break the bonds between the polar sides of the molecules . our vibration , or our kinetic energy for each molecule , still is n't strong enough to completely separate them . they 're starting to slide past each other . and this is essentially what happens when you 're in a liquid state . you have a lot of atoms that want be touching each other but they 're sliding . they have enough kinetic energy to slide past each other and break that solid lattice structure here . and then if you add even more kinetic energy , even more heat , at this point it 's a solution now . they 're not even going to be able to stay together . they 're not going to be able to stay near each other . if you add enough kinetic energy they 're going to start looking like this . they 're going to completely separate and then kind of bounce around independently . especially independently if they 're an ideal gas . but in general , in gases , they 're no longer touching each other . they might bump into each other . but they have so much kinetic energy on their own that they 're all doing their own thing and they 're not touching . i think that makes intuitive sense if you just think about what a gas is . for example , it 's hard to see a gas . why is it hard to see a gas ? because the molecules are much further apart . so they 're not acting on the light in the way that a liquid or a solid would . and if we keep making that extended further , a solid -- well , i probably should n't use the example with ice . because ice or water is one of the few situations where the solid is less dense than the liquid . that 's why ice floats . and that 's why icebergs do n't just all fall to the bottom of the ocean . and ponds do n't completely freeze solid . but you can imagine that , because a liquid is in most cases other than water , less dense . that 's another reason why you can see through it a little bit better . or it 's not diffracting -- well i wo n't go into that too much , than maybe even a solid . but the gas is the most obvious . and it is true with water . the liquid form is definitely more dense than the gas form . in the gas form , the molecules are going to jump around , not touch each other . and because of that , more light can get through the substance . now the question is , how do we measure the amount of heat that it takes to do this to water ? and to explain that , i 'll actually draw a phase change diagram . which is a fancy way of describing something fairly straightforward . let me say that this is the amount of heat i 'm adding . and this is the temperature . we 'll talk about the states of matter in a second . so heat is often denoted by q . sometimes people will talk about change in heat . they 'll use h , lowercase and uppercase h. they 'll put a delta in front of the h. delta just means change in . and sometimes you 'll hear the word enthalpy . let me write that . because i used to say what is enthalpy ? it sounds like empathy , but it 's quite a different concept . at least , as far as my neural connections could make it . but enthalpy is closely related to heat . it 's heat content . for our purposes , when you hear someone say change in enthalpy , you should really just be thinking of change in heat . i think this word was really just introduced to confuse chemistry students and introduce a non-intuitive word into their vocabulary . the best way to think about it is heat content . change in enthalpy is really just change in heat . and just remember , all of these things , whether we 're talking about heat , kinetic energy , potential energy , enthalpy . you 'll hear them in different contexts , and you 're like , i thought i should be using heat and they 're talking about enthalpy . these are all forms of energy . and these are all measured in joules . and they might be measured in other ways , but the traditional way is in joules . and energy is the ability to do work . and what 's the unit for work ? well , it 's joules . force times distance . but anyway , that 's a side-note . but it 's good to know this word enthalpy . especially in a chemistry context , because it 's used all the time and it can be very confusing and non-intuitive . because you 're like , i do n't know what enthalpy is in my everyday life . just think of it as heat contact , because that 's really what it is . but anyway , on this axis , i have heat . so this is when i have very little heat and i 'm increasing my heat . and this is temperature . now let 's say at low temperatures i 'm here and as i add heat my temperature will go up . temperature is average kinetic energy . let 's say i 'm in the solid state here . and i 'll do the solid state in purple . no i already was using purple . i 'll use magenta . so as i add heat , my temperature will go up . heat is a form of energy . and when i add it to these molecules , as i did in this example , what did it do ? it made them vibrate more . or it made them have higher kinetic energy , or higher average kinetic engery , and that 's what temperature is a measure of ; average kinetic energy . so as i add heat in the solid phase , my average kinetic energy will go up . and let me write this down . this is in the solid phase , or the solid state of matter . now something very interesting happens . let 's say this is water . so what happens at zero degrees ? which is also 273.15 kelvin . let 's say that 's that line . what happens to a solid ? well , it turns into a liquid . ice melts . not all solids , we 're talking in particular about water , about h2o . so this is ice in our example . all solids are n't ice . although , you could think of a rock as solid magma . because that 's what it is . i could take that analogy a bunch of different ways . but the interesting thing that happens at zero degrees . depending on what direction you 're going , either the freezing point of water or the melting point of ice , something interesting happens . as i add more heat , the temperature does not to go up . as i add more heat , the temperature does not go up for a little period . let me draw that . for a little period , the temperature stays constant . and then while the temperature is constant , it stays a solid . we 're still a solid . and then , we finally turn into a liquid . let 's say right there . so we added a certain amount of heat and it just stayed a solid . but it got us to the point that the ice turned into a liquid . it was kind of melting the entire time . that 's the best way to think about it . and then , once we keep adding more and more heat , then the liquid warms up too . now , we get to , what temperature becomes interesting again for water ? well , obviously 100 degrees celsius or 373 degrees kelvin . i 'll do it in celsius because that 's what we 're familiar with . what happens ? that 's the temperature at which water will vaporize or which water will boil . but something happens . and they 're really getting kinetically active . but just like when you went from solid to liquid , there 's a certain amount of energy that you have to contribute to the system . and actually , it 's a good amount at this point . where the water is turning into vapor , but it 's not getting any hotter . so we have to keep adding heat , but notice that the temperature did n't go up . we 'll talk about it in a second what was happening then . and then finally , after that point , we 're completely vaporized , or we 're completely steam . then we can start getting hot , the steam can then get hotter as we add more and more heat to the system . so the interesting question , i think it 's intuitive , that as you add heat here , our temperature is going to go up . but the interesting thing is , what was going on here ? we were adding heat . so over here we were turning our heat into kinetic energy . temperature is average kinetic energy . but over here , what was our heat doing ? well , our heat was was not adding kinetic energy to the system . the temperature was not increasing . but the ice was going from ice to water . so what was happening at that state , is that the kinetic energy , the heat , was being used to essentially break these bonds . and essentially bring the molecules into a higher energy state . so you 're saying , sal , what does that mean , higher energy state ? well , if there was n't all of this heat and all this kinetic energy , these molecules want to be very close to each other . for example , i want to be close to the surface of the earth . when you put me in a plane you have put me in a higher energy state . i have a lot more potential energy . i have the potential to fall towards the earth . likewise , when you move these molecules apart , and you go from a solid to a liquid , they want to fall towards each other . but because they have so much kinetic energy , they never quite are able to do it . but their energy goes up . their potential energy is higher because they want to fall towards each other . by falling towards each other , in theory , they could do some work . so what 's happening here is , when we 're contributing heat -- and this amount of heat we 're contributing , it 's called the heat of fusion . because it 's the same amount of heat regardless how much direction we go in . when we go from solid to liquid , you view it as the heat of melting . it 's the head that you need to put in to melt the ice into liquid . when you 're going in this direction , it 's the heat you have to take out of the zero degree water to turn it into ice . so you 're taking that potential energy and you 're bringing the molecules closer and closer to each other . so the way to think about it is , right here this heat is being converted to kinetic energy . then , when we 're at this phase change from solid to liquid , that heat is being used to add potential energy into the system . to pull the molecules apart , to give them more potential energy . if you pull me apart from the earth , you 're giving me potential energy . because gravity wants to pull me back to the earth . and i could do work when i 'm falling back to the earth . a waterfall does work . it can move a turbine . you could have a bunch of falling sals move a turbine as well . and then , once you are fully a liquid , then you just become a warmer and warmer liquid . now the heat is , once again , being used for kinetic energy . you 're making the water molecules move past each other faster , and faster , and faster . to some point where they want to completely disassociate from each other . they want to not even slide past each other , just completely jump away from each other . and that 's right here . this is the heat of vaporization . and the same idea is happening . before we were sliding next to each other , now we 're pulling apart altogether . so they could definitely fall closer together . and then once we 've added this much heat , now we 're just heating up the steam . we 're just heating up the gaseous water . and it 's just getting hotter and hotter and hotter . but the interesting thing there , and i mean at least the interesting thing to me when i first learned this , whenever i think of zero degrees water i 'll say , oh it must be ice . but that 's not necessarily the case . if you start with water and you make it colder and colder and colder to zero degrees , you 're essentially taking heat out of the water . you can have zero degree water and it has n't turned into ice yet . and likewise , you could have 100 degree water that has n't turned into steam yeat . you have to add more energy . you can also have 100 degree steam . you can also have zero degree water . anyway , hopefully that gives you a little bit of intuition of what the different states of matter are . and in the next problem , we 'll talk about how much heat exactly it does take to move along this line . and maybe we can solve some problems on how much ice we might need to make our drink cool .
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and 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 anyone know what the process is called when bec changes to solid , and when solid changes into bec ?
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