 You see those lines that are between the between the phases. These are the boundary phases, right? The phase boundaries At those points usually you have Coexistent phases like you have the liquid and the solid phase are at the boundary where the arrow is the other The other the other part where you have somewhat of a curve That's where you have the vapor liquid phase boundary now. What's so special about these boundaries well? When you start to heat up a solid I'm just going to give you guys an example when you start to heat up a solid when it's purely solid Let's say water here because we have a specific temperature at which it melts What happens is you add heat the temperature starts to rise then you reach zero degrees Celsius Even though you're adding more heat the temperature persists. It does not increase anymore. Why because now you have an equilibrium between the solid phase and the liquid phase what happens is The solid starts to convert to a liquid and if you keep on adding heat That's what's going to happen if you keep the temperature constant and you stop heating you keep it at zero degrees Celsius Equilibrium is just going to stay there. Okay, so it's always going to be a solid and a liquid So you keep on heating you reach somewhat of a steady curve for the temperature Right temperature remains constant until all the solid has converted to a liquid after that Heating will cause the temperature to rise up again Okay So you guys all know this two hundred seventy-three point fifteen Kelvin is the boy is the melting point for water, right and Three hundred seventy-three point fifteen Kelvin is the boiling point now just a tip for his exam 273 and 273 point 15 are not exactly the same Okay, so he really stresses on these values so make sure that you're the values that you use in your calculations are very accurate okay so Basically same with the solid and the liquid same thing happens with the vapor and the liquid right you reach a phase boundary where the arrow is Pointing that's where boiling starts to take place hundred degrees Celsius Temperature stays constant as you're heating until all the liquid converts to a vapor and At that point after all the liquids turn into vapor temperature starts to rise again okay, so Now you look at this You look at the first paragraph you notice it says that you can actually keep water as a liquid at two hundred eighty-five degrees Celsius That's a hundred and eighty-five degrees more than the normal boiling point, but then again look at the pressure thousand psi Right So does this make sense that liquid that you can keep water at a liquid at such a high-temperature Yes, you're exerting a very strong pressure at it right you're keeping it nice and condensed Pressure plays a very important role in the phases right the more pressurized something is the more condensed it is as in between Vapor and liquid is more liquidy between liquid and solids more solid All right the less pressure you exert the more The liquid or the water or the substance starts to expand and goes further more along the gas towards the gas phase So and I'm going to go back to the triple point So the triple the definition of the triple point as you can see it's kind of like a point at which all three phases tend to Intercept and you can see it's kind of close close to war zero degrees Celsius right if you can see from the plot Almost two hundred seventy three two hundred eighty somewhere there right So at this point the substance exists as all three exists as a solid exists as a vapor And exists as a liquid This is the definition of a triple point. What about the critical point? You notice that the critical critical point that the line kind of disappears The liquid and the vapor phase are rather indistinguishable okay, so So you kind of have them I wouldn't want to say a mixture, but you can't say if the if the Substance is a gas or a liquid Okay, so When you put water at One atmosphere one atmosphere is kind of like the standard pressure right it's the pressure that we are at When the temperatures between zero degrees Celsius and a hundred degrees Celsius What do I have have a liquid right? There is no solid. There is no vapor or let's just say let's be more accurate There's not enough solid or enough vapor that that could account to the amount in there So it's basically purely liquid below zero degrees. It's ice over a hundred degrees It's vapor Exactly at these two points and I've said this a number of times now Exactly at zero degrees Celsius the liquid or the water can exist as both liquid and ice and At a hundred degrees Celsius it can exist as both vapor and liquid Right now here. We're looking at the phase diagram for carbon now If you notice and if you paid attention in the phase diagram for water as well, you notice that ice Was existing in like about what seven phases, right? So you have seven different phases of solid ice or solid liquid that just different structures Same thing with carbon here. You have two different structures, and I think you guys know this Carbon can exist as graphite can exist as diamond now This kind of kind of shows you why diamond can be so expensive, right? I mean look at how much pressure you need to exert on Graphite to turn into into diamond. This is a very expensive procedure but nonetheless people still tend to do it and It's a very slow process requires a catalyst and so there are just a number of reasons as to why this This process is very expensive and why diamonds are so damn expensive Okay, so again as I said when you have two phases When you when you're at a phase boundary when you have your substance as a liquid and a vapor or liquid and a solid Basically, what happens is these two phases are at equilibrium The atoms or the molecules start to jump from one face to the other at random So basically what I'm trying to say is at the zero degree boundary Not all the solid remains a solid not all the liquid remains a liquid No, these atoms tend to jump around between the solid and the liquid phases So so, yeah There's an experiment that you can use in order to to validate that to validate that Not everything that's a solid remains a solid not everything. That's the liquid remains a liquid Usually what you do is you put For example, you have a certain container that contains liquid water and gas or vapor water, right? And you somehow introduce D2O. So you guys know what D is right D is deuterium. It's an isotope of hydrogen, right? and What you do is when you introduce that vapor into the into the container at some point some of the D2O vapor will convert into a liquid Now you can use mass spectrometry or you can use certain lap techniques And you will see that after some time the liquid will contain some D2O Okay, so I really what I want you to get out of this This slide over here. It's just that nothing remains the same, right? Everything is jumping between the two phases all the atoms. I guess the last sentence says it all right So for some of you this might come off as a little odd. I Know it was odd to me the first time I learned this evaporating cooling So do you know when you're when you're sweating for example when you're running in a hot day? Sweating is a very sweating is a cooling process, right? So some animals can't stand the heat some animals don't sweat dry weather. They just die out. They don't cool down So what happens basically is? Some molecules when you when you have a substance and you start to heat it up. Let's say we want to vaporize some water, okay? What happens is the molecules in the water the water molecules that have high enough energy to break through the barrier and kind of Go out into into the the atmosphere. They just leave the solution. So what happens then? What happens is all the high the higher can the higher energy molecules within the liquid go out They leave so whatever is left in the liquid is actually cooler than what it originally was, right? So and you know if it's an open container the vapor completely goes out Right, so there's no chance of the higher energy molecules to come back in again. So the water will be cooler and I Guess that's that's all I can say about about about this that is just What's it called? It's just a cooling process Okay, this kind of explains it even better so What you notice is at lower temperatures most molecules do exist at a lower temperatures But as you increase the temperature you get some somewhat of a more distributed Distributed number of atoms right the kind of the the curve kind of flattens out because now you have more molecules They're towards the higher energy end now the shaded region here the red shaded region in both graphs are basically the Molecules that have enough energy to escape the solution so imagine if these higher energy molecules escape the solution Solution is just gonna get Cool, right? now Okay Now you notice the last sentence or the second statement in this slide says molecules may escape from a solid surface to like dry ice so This is something I talked about last Not last week yesterday, right when we're talking about the dry how that guy tried to dry his clothes under 15 degrees So in negative 15 degrees Celsius weather Well, so you guys probably know this Face transitions do not necessarily have to go from solid to liquid to vapor Transition can go directly from solid to gas. This is something we call sublimation right sublimation and what is a Compound that is known for doing that under under normal circumstances carbon dioxide So carbon dioxide usually for we call it dry ice We call dry ice because the solid directly goes to the vapor phase. It doesn't even it doesn't doesn't liquefy doesn't get wet So these are all the different kinds of phase transitions that could occur As you notice all of them are practically reversible So for sublimation where you go from salt to gas you have the opposite called deposition And if you think about it the name deposition makes sense if all the gas molecules are getting deposited on a surface, right? And they kind of solidify Melting and freezing you guys already know this vaporization and condensation also assuming you guys already know this so And basically the statement up here when it says that both salts and liquids have non-zero vapor pressure This is more of an indication that sublimation can actually occur right tell you that the solid phase also can have a vapor pressure so This is a very close very a problem very close to one of your problems in the syllabus one that we did yesterday So it tells you that this guy in Wyoming decides to hang his wet blue jeans out on a line In a dry winter day at temperatures your degree Fahrenheit So that's way below the freezing point of water right I think I don't know Fahrenheit very well But I'm assuming this is lower than the freezing point of water The jeans first freeze, but then they dry out So how can we explain this? I just looking for one word Sublimation right what happens is the temperature is too low for those wet clothes or not I don't want to say what clothes let me rephrase that So the wet clothes you put them out at zero degrees Fahrenheit. They're gonna freeze right? All the water that was in the liquid phase going to turn into a solid phase Problem is the temperature is too low For the solid or for the ice to go into melting to go into a liquid and then go to a vapor What happens it directly goes into a vapor now honestly They won't be comfortable to wear. They're gonna be very stiff and rigid you guys can give it a shot if you want It's a very slow process you can't ensure that all of it all of it would dry out It'll just be like wearing cardboards for for pants basically Yeah So the same happens with the freeze-dried food Okay, so also you what happens is water is taken off at low temperatures So that the vote so that the food doesn't get cooked up until you want to actually eat it right But the texture is quite different same with the pants relative humidity so Let's see If you're at a summer day and the relative humidity is rather high Evaporative cooling is slowed down. Why? Because it's all about equilibrium if you have a lot of vapor in the air chances are Liquid is not going to go into the vapor phase the vapor phase is kind of saturated Especially when you have above a hundred percent humidity, right? So you don't cool off why because it's not favorable when you have dry weather Evaporative cooling is more likely to occur why because you don't have a lot of water in the vapor phase. There is no humidity Right, so I guess this is just just a fun fact why you feel hotter when there's higher humidity Well because you don't sweat as much so even when relative humidity is greater than a hundred percent could almost rain because Want to think of that vapor and the atmosphere is just dying to turn into a liquid So you get immediate rain now we Went over the fun facts going to go into more math here and this is a very important equation I Suggest you guys know it very well. I can tell you this gonna give you a sneak preview something like this is gonna come on the exam So Basically, I don't know if you guys have heard of the Gibbs free energy But the Gibbs free energy is basically a function a very simple function of enthalpy and entropy Okay, so it's not only a function of energy. It's also a function of disorder, right So and this gives free energy basically this function kind of determines whether or not the process is going to be spontaneous how It's called the G by the way Delta G is negative Spontaneous positive not spontaneous negative means you're going from a hot from high energy to low energy Positive low energy to high energy. So what happens when Delta G is equal to zero? equilibrium both processes are favorable, right so Let's say you have Certain equilibrium between a liquid and a vapor, right? You can use this equation to be able to determine for example Which is a function of the vapor pressure and the temperature to be able to determine your? Heat or your energy of vaporization, and you will see why this is important So before I go further with the slides if you look at this equation right here You notice it looks like an equation of a straight line with a negative slope, right? Your why your y is your negative natural log of P Your x is 1 over t sees your intercept Negative Delta H over R is your slope from simple math, you know if you're given a certain number of or a certain table of Values for y and x can determine the slope or as a constant can determine your Delta H, right? So let's just see how this can be done so To make sure that what you're writing out is correct or to make sure that you're getting a right result You should always see a straight line With a negative slope hopefully So as I said before You let your y equal to the natural log of P your x is 1 over t your slope is negative Delta H over R and Finally your intercept is C, right? So you plot y versus x you get a certain slope Which is negative Delta H over R? Now Okay, this this this is not this is not supposed to be hard for you guys But now we want to understand where this Clausius Clapeyron equation came from So basically the most important assumption you use for this equation to satisfy Is treating your vapor is treating your substance or your fluid as an ideal gas So when you say ideal gas, what does that mean two things volume of your Particles is negligible compared to the volume of the compare a container, right? and Another thing you should take into account is that you assume that the vapor Expands much faster or expands at a higher rate than the liquid and therefore will occupy a much larger volume than the liquid So you can consider the liquid volume almost negligible compared to it and You consider that the molar enthalpy of vaporization is independent of temperature Otherwise Delta H is no longer a constant you can't include it in your slope So This should be a good hint. He tells you this is this is an exam problem that can come up, right? It gives you two pressures two temperatures, right so two points on that straight line and He can ask you to determine the Delta heat of vaporization Actually, you just want to think of it as a plug-and-chug kind of question, right? He gives you a set of values or a set of variables and ask you to solve for one of the constants Well, he might ask you guys to solve for the rate constant R for a constant Sorry for the gas constant R, right? You'll give you a certain heat of vaporization Two pressures at two different temperatures solve for now So this is a practice problem Let's say a compound is unstable as its normal boiling point Right? It's unstable. That means it's reactive. So Your compound is not what it is you want to purify it by distilling the material at reduced pressures, so Let's say we want to purify H2O2 The normal boiling point for H2O2 is 150.2 degrees Celsius But this is a very high temperature and if you guys don't know H2O2 is Let's just say a very scary compound So it has a lot of explosive risk at very high temperatures. So We want to try to purify H2O2 By letting it boil at a lower temperature. How do we do that? Let's try to think about it logically. Do we need a higher pressure or a lower pressure? Do we want to condense it more? Do we want to vaporize it more? Well We'll just see in a sec. So we want to determine what pressure should we distill H2O2 if we want to operate at 30 degrees Celsius so We want to boil this at a very low temperature and They give you the delta heat of vaporization and it's in calorie per grams now I'm assuming he's since he told you guys you're not responsible for numbers that much He's probably going to give you the conversion. All right, so you are going to know how to convert from calories to Joules and I'm assuming you guys already know how to convert from grams to Moles if you're given the molar mass so This is what we do a convert your delta heat Into a what's it called into Joules and Since you have the molar mass and you have the grams you can determine the moles Then you plug that into your cc equation now notice how he put it This is how he wants you to answer your questions on the exam He wants you he doesn't want you to to write out the equation like so Right and then rearrange it for your value while keeping the other ones as you know as Non-numeric terms. No, he just wants you to write Directly set up your problem right directly on the paper and Directly plug in your numbers just as he did here. It saves a lot of time So so notice the pressure that we have to deal with so you notice that your pressure is almost 0.01 Atmospheres very low compared to what it usually is at high temperatures, right and that makes sense because if you're exerting a very small pressure Your substance can boil at a very low temperature, right? So I'm just gonna leave this here for a sec. So you guys take note of it So never solve the equation symbolically directly substitute the when you can directly substitute your numbers Okay So by the way before I continue does every anybody have any questions so far? We can go back as far as you guys want we can go back Again, I said it first. I'm gonna say it again If you guys want me to slow down you guys want me to stay on one slide so you can take enough notes Just let me know okay. We have a lot of time I Can slow down is there any slide you guys wish to go back to and kind of go over again All of them really I'm going that fast Okay I'm sorry about that. Let's see Okay, so Yes, don't call me professor, please Just call me Muhammad. Okay That's very true. Okay Okay, I'm kind of feeling bad now. I'm going too fast. All right, so guys really I want you guys to try to tell me what Let me go through the house almost done But anyway, we have a lot of time and what I can do is I can go back We can kind of like go over certain things that you that I went over too fast. Okay So Think of it like a Two lectures in a row. How does that? How does that sound like? Terrible right terrible Okay, anyway So now these are a couple of notes that so this is something I said in the very beginning of the lecture right said That when you need to around when you when you want to solve out a numeric equation or a numeric problem I told you two seventy three point fifteen two seventy three actually make a difference So what he usually wants you to do is Don't round your numbers till you get to the very end of the or the very last step of your calculations okay, so Like he would he even said that specifically like if you can put all the numbers in the calculator that appear on the calculator You can put all those numbers in you go ahead and do that. Okay, and leave the rounding step to the very very last one now You guys have to pay attention to this equation here the Klaus-Clapeyron equation because we only talked about Vaporization Delta H of vaporization right Now let's say we're converting from solid to liquid turn it off or just solid or something. Okay Let's say I want to deal with a different process. Let's say I want to I want to discuss melting or freezing. I Don't use the same Delta heat right. I use a different Delta heat. Which one? Fusion or melting basically the same just opposite times, right? Another thing that you guys should probably know because he might give you a problem Where you have a sublimation experiment going on But instead of giving you the Delta heat of sublimation you get to the Delta heat of fusion and the Delta heat of vaporization now logically speaking Sublimation is kind of like taking a shortcut to a two-step process, right? Because the solid first or conventionally should first melt Then after it melts should vaporize If you're doing that in one step, it's just going to be the sum of the two, right? Makes sense. Okay. Now If you remember I talked about the Gibbs free energy I Said that the Gibbs free energy is Basically a measure of how spontaneous a reaction can be And as you can see it's a function of Delta H, which is your enthalpy and A function of Delta S, which is your entropy Now we said at equilibrium Delta G is equal to zero Why? Because both processes have the same relative disorder or have the same relative enthalpy So when do you have equilibrium in terms of phases? Well when you have a phase transition when sublimation is occurring When melting is occurring few when fusions are occurring vaporization or condensation, right? so at these specific phase transition points or In let's generalize more in the case where you have an equilibrium What you can do is you can actually solve You can put you can set up the equation as such where you can find the temperature at equilibrium You can find the Delta heat at equilibrium or the Delta acid equilibrium, right? so really simple Really simple concept and it just goes on or just comes from the fact that Delta G is equal to zero, right? Yes The numbers so as I told you so can I go back to the previous slide or somebody slipped my throat? Oh, thank you. Okay. Let's see which slide you mean the one with the problem Here, okay, so remember He said that in his first lecture. I think are the second one. He said that You guys don't have to know the numbers numbers will be given now They gave you here What's it called they told you normal boiling point? What is a normal boiling point? What does a normal boiling point occur? What's the pressure? One atmosphere, right? It's just a standard pressure. So you guys should know this. It makes sense He gave you a temperature. What do you do with that temperature? He converted to Kelvin, right? He said always convert our temperatures to Kelvin What else he gave you the other temperature that you need to find, right? Which in this case is 30 degrees Celsius So these numbers are given he even gave you delta H. It's probably most likely going to give you the conversion Okay, so that's why I always say pay attention to the units Because even if you have no idea what the question is asking even if you have no idea what these numbers mean You can do some unit analysis and know what you need to get like he can tell you You have Cal calories you have grams you have joules per mole. I want you to give me kilo joules How do I do that? Here's a set of converges you look at it your reason it out You see what's supposed to cancel with what and you should be able to get your answer. Yes Okay, so just to be on the safe side Anytime you're dealing with temperature always convert to Kelvin unless otherwise stated Pressure see this is the thing with pressure. He's on the exam He's gonna let you know but if he doesn't tell you like I want this in these units or this in these units You don't need to worry about but I know him. He's a very he's very efficient So he would probably tell you in what units he wants you to to get like how many milliliters of this How many kilo joules per mole will you get? You know, so he'll give you the units that you need to get eventually if he doesn't This is on me on the video camera. So a My responsibility if you're not required or he doesn't ask or it's not obvious that you need to express your Answers in a certain unit you express it in any other unit you want. Okay, but Calvin always temperature. It's always in Calvon, right? Yeah, so anyway to go back to your question So all this given over here along with the conversion That they did up here for the calories to joules That's all you really needed to get that answer now I'm assuming we have done enough exercises for you guys to know The value of the gas constant even though I'm pretty sure he's probably going to be given on the exam. Yes Hmm. Well, let me let you know a little secret Okay, it probably doesn't really matter. So let's see He says the normal boiling point is 150.2 degrees Celsius, right? And has a pressure of one atmosphere. So that's your P1 and your T1 for example 30 degrees Celsius tells you you have okay. This is your T2 right and you want to find your P2 so What is happening to the temperature? The temperature is going down, right? so We said that T1 is 150 and T2 is 30, right? Why how do I know this because he's telling you this is the initial temperature 150 and it's going down to 30 You want to take it down to 30? Okay, so basically whatever is stated for you should be able to tell from the wording of the problem I don't know if you couldn't tell from here but But you see it doesn't matter remember Boiling is going to happen. This is the Delta H of vaporization, right? Boiling point is going to happen for a certain pressure and a temperature right a point. It's a straight line Delta H is constant, right? So it doesn't matter which ones your P1 which ones your T which ones your P2 as long as they're in this form Right, so you can't like for example put your your P1 as one atmospheres and your T1 as 30. No Okay But other than that it doesn't really matter. Yes. Oh That's probably a typo because it's he says here. It's 30 degree Celsius Okay, okay Don't worry. I will go over the slides. Yes Delta s is your entropy Okay, basically a measure of disorder no hands Okay Delta G Delta G is your Gibbs free energy. Okay now question Anybody's okay Delta what and what Melting you know what melting is right fusion You don't Okay, melting is when solid goes to a liquid fusion is going to be Fusing together combining together Just the opposite So liquid to solid right now here's there's a I think here. There's another typo So Boil and vaporize are basically the same thing, right? So I would go with boil and condense and condensation or vaporization and condensation. Okay, so One of these two pairs down here has to be different it has to be condensation Okay, but I mean if you guys understand the concept that's all that's important. Okay, and Don't worry again as I said, I'm gonna go back to previous slides I'm gonna make sure you guys get some good notes. Don't worry about it now true Don's law or truth is rule and this usually applies to liquids who tend to tend to you to usually be like Tend to act a little ideally, right? So for example water doesn't apply here because you have a lot of hydrogen bonding. Let's put it this way True thons rule applies to molecules or applies to compounds that are technically don't do hydrogen bonding because there are molecules that don't Relatively interact with each other very much. Remember. That's one of the things about ideal gases or ideal fluids molecules don't interact with each other so a liquid and a gas Are both basically disordered phases, right? The solid is the only ordered phase If you put a water if I hit a water a glass of water on the on the table It's gonna get irritated if I do that for a solid or for ice ice is just gonna stay the same It's not gonna budge, right? So they're both this order only difference is one is condensed The other one is non-condensed right, so The entropy of vaporization is basically the same For a lot of molecules that don't have a lot of interaction between each other Because basically If you're going because remember heat of vaporization is going from a liquid to a solid if we're from a liquid to a vapor So when we're saying that they're both disordered, right? so The only thing that's really changing is whether there is it being condensed to it being non-condensed, right? So and this is usually very similar in the case of all molecules. So I guess what I'm trying to get at is That Trouton's rule tells you is that the entropy of vaporization for most molecules or most types of compounds is relatively the same Because the only thing that's changing is how condensed it is and how it can this is not going to be right Which is a very similar phenomenon for most molecules and usually the value for that molar entropy is 87 87.5 joules per mole per Kelvin For most molecules add that specific pressure and add their normal boiling point Okay So really all you really need to get out of this slide you need to understand is That unless hydrogen bonding is involved and here of course you're doing an approximation Because they're not going to be exactly 87.5, but unless hydrogen bonding is involved unless the interaction between these molecules is strong The entropy is constant. Okay, so I'll show you how this can apply Exactly, so the heat of vaporization is what's different not the entropy. So what we're saying basically is since both of them are disordered The entropy is gonna say the same because the entropy is only a measure of the disorder, right? It's the it's the energy of vaporization that changes between one compound to the other so This is a good practice problem to understand the the the the method so They're asking you to find the normal boiling point of hydrogen sulfide and of argon Knowing their enthalpies of vaporization are 18.6 and 6.4 kilojoules per mole right now Remember when we said delta G is equal to zero which happens for most phase transitions or equilibria You can relate the temperature to the enthalpy and to the entropy right T Boil for example is equal to delta H boil or over delta S boil Here they're asking us to find T boil they gave us delta H boil What do we need? Well? We need the entropy, right? But since we said and we made that assumption according to true toss rule that the disorder or the change in disorder is basically the same For both so you consider delta S for these molecules to be or delta S of vaporization So I'm really stressing on this. It's just the delta S of vaporization You consider it to be a constant so for both of them is eighty seven point five Just plug them into the equation and make sure you transfer you make sure your temperature is in Kelvin You solve away and you should be able to find it Does it make sense? Yes, I want to hear a unified. Yes, okay. Thank you All right, so are we all good? No No, one more point as you notice they gave us the true values down here You see that they're kind of different. They're not so they're very close, but they're not exactly the same That's why it's an approximation Okay They can't all exactly have eighty seven point five Okay No So this one this is what I was talking about So as far as you guys need to know as long as it doesn't do hydrogen bonding Triton's law applies Why? Because water is a little bit for example water does hydrogen bonding any Molecule with hf in it is basically also What's it called hf molecules are also do hydrogen bonding And anything that has an NH bond also does hydrogen bond right you guys should know this So we know that a hydrogen bond is a strong type of intermolecular force And so what it does is it makes the liquid a little more ordered than it's then it's supposed to be right and Therefore it doesn't two tons law doesn't apply for them so This order is disrupted going to the vapor pressure where there's no hydrogen bonding but With these liquids or with With things that actually do hydrogen bonding The order takes a while to get disrupted So notice how how large the entropy is of vaporization for water It's a hundred kilo joules per Kelvin per mole as compared to eighty seven point five. It's not very low So it would likewise be higher for other liquids that show hydrogen bonding Okay, so this is an easy thing to understand. It shouldn't be too Too terrible or too difficult So are we all good on this slide? No Can you repeat that? Okay, because they're considering it as the molar entropy of vaporization. This is the entropy per mole Right that small m is not there. It's just going to be joules per kelp Okay, so notice there's a difference in the units between What's it called between entropy and enthalpy can somebody tell me why Why is there a difference between entropy and enthalpy? What's the difference? Well in turn the units can help you determine what is different and it's something I said in the previous slide in a previous slide So What's the unit of enthalpy joules per mole right or joules? It's a unit of energy. What about entropy? Joules per Kelvin It's not exactly unit of energy. It's an important thing for you guys to know That's why we got we multiplied by the temperature in the Delta G equation because Delta G or G gives free energy It's an energy value, right? So when you multiply your entropy, I'm just going to go back. I'm going to come back here Here notice is Delta H minus T Delta S. So let's do a little unit analysis. This is kind of like a practice for you guys Delta S is joules per Kelvin Multiplied by temperature. What does it turn into? Joules right so it's an energy term now Yes Huh This is an enthalpy of vaporization enthalpy vaporization chain is it's different. So How though? How is it different from what so entropy? Okay, so the Gibbs free energy combines two different factors For determining whether a process is going to be spontaneous or not spontaneous There are two things that you should know about spontaneity, right? Hey Something becomes more disordered. It's more spontaneous, right? If you put some salt and you put some pepper over it right over it you shake it up You're not going to have a layer of salt and layer of pepper, right? They're going to mix up together, right? Why because it's more spontaneous to have more disorder and that's what Delta S is some measure of disorder now Enthalpy on the other hand some measure of energy, right? Energy is a different term when something has higher energy. It's less stable less spontaneous Okay, if anybody wants to raise their hand please raise it higher Okay So are we good here? so this is a good this is a good way of Demonstrating how hydrogen bonding disrupts the trend So you notice that they have a really high boiling point, right? molecules that tend to have high Hydrogen bonding have a harder time breaking apart when you heat them up, right now This is a question. You guys know electronegative in terms of electronegativity Fluorine is more electronegative than oxygen is more electronegative than nitrogen, right? Why is H2O at a higher boiling point than hydrogen fluoride? Hmm, so yes, it has more it's more opportune to do hydrogen bonding, right has two hydrogens Two lone pairs has more chance of doing hydrogen bonding, right? And so it helps things more tightly exactly and this is something I guess you guys already know as well But decreasing the molar mass also leads to a decrease in the boiling point So this is an important thing you guys should know as well Okay, now of course this decreasing in the molar mass does not apply as you can see does not apply to the things that hydrogen Bond we're talking for ordinary molecules, right? Because you can see it kind of shoots up when you start doing hydrogen bonding. Are we all okay? Thank you. All right Okay, so can somebody tell me why methane does not follow the H bonding trend means bond it for hydrogens I think it might do a little hydrogen bonding Why? anybody you Exactly so carbon is not electronegative enough To polarize it to polarize the hydrogen enough for it to do hydrogen bonding, so Guess these are a couple of things you guys should know before you go into the exam Condensed phases are far more complex than gasses right Gasses are easy to study pv equal nrt Condensed matter in best phases they take they're much more complicated So you know that according to the phase diagram Two phases can coexist, but only at a certain point, right? So for a given pressure you need a given temperature for two phases to exist and I'm going to go over that again now We do not yet have a good theory to be able to predict for example that water should freeze at 20 273.15 Kelvin at one atmosphere How do we do that or how do we get this? By experiment now The fourth bullet point it kind of tells you an important thing that you should know about X-ray diffraction its use why do we do X-ray diffraction? What it simply does it determines the structure of your solids because we said that solids that tend to crystallize Then to crystallize in certain structures And it's important for application purposes to understand Why or not understand why but understand how the solid crystallizes? It's important to know why iron forms a body-centered cubic structure, right why sodium chloride has somewhat of a face-centered cubic structure again last point and I guess you guys should know this like Followed your hand The unit cell is the smallest unit in a crystal and we said stayed in the bullet point above it Solid is a regular periodic array So it's basically a set of these repeating unit cells, right? So the whole 3d lattice is basically just made up of copies of those of that specific unit cell So how is that helpful? Why would I want to know this? Well because it means that you can isolate a single unit cell and just knowing how that unit cell looks like Just knowing and just knowing all kinds of information and properties about that unit cell You can generalize it and determine a more general Get a more general idea about how the crystal looks like or the properties about those crystals Okay so I'm going to go back to some slides that I feel I need to need to go over more all right and Very democratic, so if you guys Choose or there's something in specific you want me to go over. Please feel free to tell me Okay So as long as we're all okay on this slide, I'd like to go back to the top Is everybody okay with that? No You're a no or yes Yes, okay