WEBVTT 00:00:00.000 --> 00:00:02.940 align:middle line:90% [SQUEAKING] 00:00:02.940 --> 00:00:04.410 align:middle line:90% [RUSTLING] 00:00:04.410 --> 00:00:12.250 align:middle line:90% [CLICKING] 00:00:12.250 --> 00:00:15.020 align:middle line:84% RAFAEL JARAMILLO: Good, all right, so let's get started. 00:00:15.020 --> 00:00:17.780 align:middle line:84% Today is lecture 2, 3020, and we're 00:00:17.780 --> 00:00:19.780 align:middle line:84% going to talk about the scope of thermodynamics. 00:00:19.780 --> 00:00:21.580 align:middle line:90% And one last note-- 00:00:21.580 --> 00:00:24.190 align:middle line:84% I'm in another location, so getting 00:00:24.190 --> 00:00:27.027 align:middle line:84% used to the configuration here with the camera. 00:00:27.027 --> 00:00:29.110 align:middle line:84% My face is hidden behind the camera half the time. 00:00:29.110 --> 00:00:30.040 align:middle line:90% I'm sorry for that. 00:00:30.040 --> 00:00:33.650 align:middle line:84% I think that by Monday I'm going to have this all worked out. 00:00:33.650 --> 00:00:35.857 align:middle line:84% But at least you can see me, so there we go. 00:00:35.857 --> 00:00:37.690 align:middle line:84% All right, so what does thermodynamics treat 00:00:37.690 --> 00:00:38.920 align:middle line:90% and what does it not? 00:00:38.920 --> 00:00:41.343 align:middle line:84% That's the topic of the day, the scope of thermodynamics. 00:00:41.343 --> 00:00:43.510 align:middle line:84% So first we're going to talk about states of matter. 00:00:43.510 --> 00:00:50.290 align:middle line:90% 00:00:50.290 --> 00:00:52.142 align:middle line:90% What is a state of matter? 00:00:52.142 --> 00:00:54.100 align:middle line:84% There's different ways to define it, of course, 00:00:54.100 --> 00:00:55.808 align:middle line:84% but we're going to define it as something 00:00:55.808 --> 00:01:07.640 align:middle line:84% that has well-defined responses to, let's 00:01:07.640 --> 00:01:29.070 align:middle line:84% say, squeezing, heating, adding more of the same stuff, 00:01:29.070 --> 00:01:32.750 align:middle line:90% and adding different stuff. 00:01:32.750 --> 00:01:38.750 align:middle line:84% And we're using colloquial language here, 00:01:38.750 --> 00:01:42.020 align:middle line:84% but there is way that matter responds to stimuli 00:01:42.020 --> 00:01:44.640 align:middle line:84% like these is characterized by response functions. 00:01:44.640 --> 00:01:46.140 align:middle line:84% And we're going to write these down. 00:01:46.140 --> 00:01:48.182 align:middle line:84% So these are the types of things that we're going 00:01:48.182 --> 00:01:50.080 align:middle line:90% to do throughout the term. 00:01:50.080 --> 00:01:55.450 align:middle line:84% Another thing that we often do to states of matter 00:01:55.450 --> 00:01:57.070 align:middle line:90% is we apply fields. 00:01:57.070 --> 00:01:58.570 align:middle line:90% We don't treat that in 020. 00:01:58.570 --> 00:02:01.480 align:middle line:84% We don't get there, but the types of fields we might apply 00:02:01.480 --> 00:02:03.410 align:middle line:84% are strange fields, gravitational fields, 00:02:03.410 --> 00:02:05.830 align:middle line:84% magnetic fields, or electric fields. 00:02:05.830 --> 00:02:08.620 align:middle line:84% We might just get to a little bit of electrochemistry 00:02:08.620 --> 00:02:09.830 align:middle line:90% in the class. 00:02:09.830 --> 00:02:10.970 align:middle line:90% We'll see if we get there. 00:02:10.970 --> 00:02:12.553 align:middle line:84% But, otherwise, we're not really going 00:02:12.553 --> 00:02:15.290 align:middle line:84% to spend time talking about applying fields. 00:02:15.290 --> 00:02:19.000 align:middle line:84% So we have this stuff, and we're characterizing it. 00:02:19.000 --> 00:02:23.230 align:middle line:84% And we characterize it by how it responds. 00:02:23.230 --> 00:02:27.990 align:middle line:84% So that's one thing that thermodynamics treats. 00:02:27.990 --> 00:02:32.710 align:middle line:84% Thermodynamics also treats transformations between states. 00:02:32.710 --> 00:02:45.420 align:middle line:90% 00:02:45.420 --> 00:02:47.370 align:middle line:90% So this is pretty generic. 00:02:47.370 --> 00:02:51.840 align:middle line:84% We have some state A, and it transforms to some state 00:02:51.840 --> 00:02:56.860 align:middle line:90% B. It treats transformations. 00:02:56.860 --> 00:03:11.690 align:middle line:84% So we have starting and final states described certainly. 00:03:11.690 --> 00:03:15.090 align:middle line:90% 00:03:15.090 --> 00:03:18.240 align:middle line:84% So we have certainty over what those states are, 00:03:18.240 --> 00:03:21.040 align:middle line:90% how they behave. 00:03:21.040 --> 00:03:22.900 align:middle line:84% These diagrams are really useful for that. 00:03:22.900 --> 00:03:25.480 align:middle line:84% You say here's the state that you expect. 00:03:25.480 --> 00:03:27.590 align:middle line:84% Let's change the temperature pressure. 00:03:27.590 --> 00:03:29.720 align:middle line:84% Here's the final state that you expect. 00:03:29.720 --> 00:03:35.500 align:middle line:84% So we can use phase diagrams to make these predictions 00:03:35.500 --> 00:03:36.310 align:middle line:90% with certainty. 00:03:36.310 --> 00:03:39.930 align:middle line:90% 00:03:39.930 --> 00:03:43.550 align:middle line:84% One thing that's-- and knowing about thermo when you first 00:03:43.550 --> 00:03:52.590 align:middle line:84% learn it is that the process is abstract, 00:03:52.590 --> 00:03:56.310 align:middle line:84% meaning thermo tells you how things start out and how they 00:03:56.310 --> 00:03:56.940 align:middle line:90% end up. 00:03:56.940 --> 00:04:00.420 align:middle line:84% But a process of transformation-- 00:04:00.420 --> 00:04:02.010 align:middle line:84% it's very much a black box in thermo, 00:04:02.010 --> 00:04:03.728 align:middle line:90% and we don't really treat it. 00:04:03.728 --> 00:04:04.770 align:middle line:90% There's a class for that. 00:04:04.770 --> 00:04:05.640 align:middle line:90% It's kinetics. 00:04:05.640 --> 00:04:08.820 align:middle line:84% You take it in the fall, so we'll be specific. 00:04:08.820 --> 00:04:15.770 align:middle line:90% Kinetics is not described. 00:04:15.770 --> 00:04:20.110 align:middle line:90% 00:04:20.110 --> 00:04:24.015 align:middle line:90% There's no time in thermo-- 00:04:24.015 --> 00:04:27.348 align:middle line:90% 00:04:27.348 --> 00:04:29.640 align:middle line:84% at least in equilibrium thermo-- when you first see it, 00:04:29.640 --> 00:04:30.900 align:middle line:90% like in 020. 00:04:30.900 --> 00:04:32.730 align:middle line:90% So we will never do this to you. 00:04:32.730 --> 00:04:35.290 align:middle line:90% 00:04:35.290 --> 00:04:37.040 align:middle line:84% Never going to do that-- we're never going 00:04:37.040 --> 00:04:38.248 align:middle line:90% to take any time derivatives. 00:04:38.248 --> 00:04:40.340 align:middle line:84% We're never going to calculate rates. 00:04:40.340 --> 00:04:44.230 align:middle line:84% We only calculate what you get at the end of a process 00:04:44.230 --> 00:04:46.028 align:middle line:90% if you wait sufficiently long. 00:04:46.028 --> 00:04:46.820 align:middle line:90% What is sufficient? 00:04:46.820 --> 00:04:47.650 align:middle line:90% I don't know. 00:04:47.650 --> 00:04:52.773 align:middle line:90% 00:04:52.773 --> 00:04:54.190 align:middle line:84% This is one way to think about it. 00:04:54.190 --> 00:05:03.480 align:middle line:84% Thermo describes the why and only hints at the how. 00:05:03.480 --> 00:05:09.820 align:middle line:90% 00:05:09.820 --> 00:05:13.067 align:middle line:84% I find this an interesting way to remember what thermo does 00:05:13.067 --> 00:05:13.900 align:middle line:90% and what it doesn't. 00:05:13.900 --> 00:05:17.620 align:middle line:84% So, for instance, when we rupture the hot pack 00:05:17.620 --> 00:05:21.190 align:middle line:84% or we rupture the cold pack, we could understand 00:05:21.190 --> 00:05:22.660 align:middle line:90% those spontaneous reactions. 00:05:22.660 --> 00:05:23.740 align:middle line:90% We understood why. 00:05:23.740 --> 00:05:25.900 align:middle line:84% One of them was driven by entropy. 00:05:25.900 --> 00:05:27.430 align:middle line:90% The other was driven by energy. 00:05:27.430 --> 00:05:28.540 align:middle line:90% That was the why. 00:05:28.540 --> 00:05:30.903 align:middle line:84% But the how, we didn't talk about it. 00:05:30.903 --> 00:05:32.320 align:middle line:84% In fact, somebody thankfully asked 00:05:32.320 --> 00:05:33.770 align:middle line:90% me a question how that worked. 00:05:33.770 --> 00:05:35.650 align:middle line:84% What was actually going on inside the bag? 00:05:35.650 --> 00:05:37.817 align:middle line:84% It had to do with two different bags and the surface 00:05:37.817 --> 00:05:40.410 align:middle line:90% preparation and supersaturation. 00:05:40.410 --> 00:05:42.230 align:middle line:84% Thermo doesn't really treat the how. 00:05:42.230 --> 00:05:43.615 align:middle line:90% It just gives you some ideas. 00:05:43.615 --> 00:05:45.740 align:middle line:84% So it's a starting point for understanding the how, 00:05:45.740 --> 00:05:47.150 align:middle line:90% but it does tell you the why. 00:05:47.150 --> 00:05:51.840 align:middle line:90% 00:05:51.840 --> 00:05:53.850 align:middle line:84% All right, what about the use of thermodynamics? 00:05:53.850 --> 00:06:07.140 align:middle line:84% You're here-- you're here because thermo is useful. 00:06:07.140 --> 00:06:10.730 align:middle line:84% It's really useful, whether you become scientists or engineers. 00:06:10.730 --> 00:06:13.430 align:middle line:90% 00:06:13.430 --> 00:06:15.930 align:middle line:84% It's really useful, and that's why we make you take it. 00:06:15.930 --> 00:06:17.220 align:middle line:90% So how is it useful? 00:06:17.220 --> 00:06:18.460 align:middle line:90% How do we use it? 00:06:18.460 --> 00:06:23.355 align:middle line:84% We use it to predict and control matter. 00:06:23.355 --> 00:06:30.580 align:middle line:90% 00:06:30.580 --> 00:06:33.190 align:middle line:84% And we use it to transfer knowledge-- 00:06:33.190 --> 00:06:39.520 align:middle line:90% 00:06:39.520 --> 00:06:43.710 align:middle line:84% again, an example being phase diagrams, 00:06:43.710 --> 00:06:45.720 align:middle line:84% which are great summaries of knowledge. 00:06:45.720 --> 00:06:48.565 align:middle line:90% 00:06:48.565 --> 00:06:49.815 align:middle line:90% So let me give you an example. 00:06:49.815 --> 00:06:53.310 align:middle line:90% 00:06:53.310 --> 00:06:57.720 align:middle line:84% Let's have it a temperature axis here. 00:06:57.720 --> 00:07:02.960 align:middle line:84% This is temperature in degrees C. 00:07:02.960 --> 00:07:07.410 align:middle line:84% And we're going to study water at one atmospheric pressure. 00:07:07.410 --> 00:07:11.345 align:middle line:84% So it's one-dimensional system here, temperature. 00:07:11.345 --> 00:07:16.617 align:middle line:90% 00:07:16.617 --> 00:07:17.575 align:middle line:90% And here it is boiling. 00:07:17.575 --> 00:07:20.360 align:middle line:90% 00:07:20.360 --> 00:07:23.220 align:middle line:84% All right, so what is the freezing point of water? 00:07:23.220 --> 00:07:23.880 align:middle line:90% Somebody? 00:07:23.880 --> 00:07:24.930 align:middle line:90% You know this. 00:07:24.930 --> 00:07:27.650 align:middle line:84% What's the freezing point in water in C? 00:07:27.650 --> 00:07:29.100 align:middle line:90% AUDIENCE: 0 degree Celsius. 00:07:29.100 --> 00:07:29.700 align:middle line:90% RAFAEL JARAMILLO: Zero, right. 00:07:29.700 --> 00:07:31.380 align:middle line:84% I'm freezing right now in this basement 00:07:31.380 --> 00:07:33.060 align:middle line:90% in the woods in Vermont. 00:07:33.060 --> 00:07:35.400 align:middle line:90% So I'm freezing. 00:07:35.400 --> 00:07:37.310 align:middle line:84% What about if we're here in the summer? 00:07:37.310 --> 00:07:41.620 align:middle line:84% It wouldn't be boiling, but what is the boiling point 00:07:41.620 --> 00:07:43.670 align:middle line:90% of water in degrees C? 00:07:43.670 --> 00:07:44.900 align:middle line:90% 100, someone put the chat. 00:07:44.900 --> 00:07:47.703 align:middle line:84% Well, I don't really monitor the chat. 00:07:47.703 --> 00:07:50.120 align:middle line:84% Not because I'm anti chat-- it's just one too many screens 00:07:50.120 --> 00:07:51.078 align:middle line:90% cluttering up my thing. 00:07:51.078 --> 00:07:53.630 align:middle line:84% So next time, please use the mic. 00:07:53.630 --> 00:07:55.080 align:middle line:90% But yeah, it's 100. 00:07:55.080 --> 00:07:55.580 align:middle line:90% Thanks. 00:07:55.580 --> 00:07:57.300 align:middle line:90% So here's a question. 00:07:57.300 --> 00:08:00.780 align:middle line:90% How did you know that? 00:08:00.780 --> 00:08:04.080 align:middle line:84% Anyone who just did a quantum chemical calculation 00:08:04.080 --> 00:08:06.480 align:middle line:84% from first principles, I want you to raise your hand. 00:08:06.480 --> 00:08:09.570 align:middle line:90% 00:08:09.570 --> 00:08:11.510 align:middle line:90% Nobody did that. 00:08:11.510 --> 00:08:13.670 align:middle line:84% In fact, if you did, you'd probably 00:08:13.670 --> 00:08:16.860 align:middle line:84% be writing a paper right now because that's still a very, 00:08:16.860 --> 00:08:18.523 align:middle line:90% very, very hard calculation. 00:08:18.523 --> 00:08:20.690 align:middle line:84% In fact, I've never seen it-- an accurate prediction 00:08:20.690 --> 00:08:23.180 align:middle line:84% of the freezing point of a liquid 00:08:23.180 --> 00:08:26.370 align:middle line:84% from first principles using theory. 00:08:26.370 --> 00:08:29.780 align:middle line:90% So how did you know that? 00:08:29.780 --> 00:08:33.270 align:middle line:84% AUDIENCE: These are material properties of water. 00:08:33.270 --> 00:08:34.340 align:middle line:84% RAFAEL JARAMILLO: These are the material properties of water. 00:08:34.340 --> 00:08:35.840 align:middle line:84% You know that because you know that. 00:08:35.840 --> 00:08:38.704 align:middle line:84% And you know that because the data that's out there you 00:08:38.704 --> 00:08:39.617 align:middle line:90% have access to. 00:08:39.617 --> 00:08:41.450 align:middle line:84% Materials have properties, and some of these 00:08:41.450 --> 00:08:43.825 align:middle line:84% are so commonplace that you know them without having ever 00:08:43.825 --> 00:08:45.840 align:middle line:90% taken a class. 00:08:45.840 --> 00:08:47.402 align:middle line:90% So these are observations. 00:08:47.402 --> 00:08:48.360 align:middle line:90% These are observations. 00:08:48.360 --> 00:08:52.340 align:middle line:84% These are two of the huge number of observations 00:08:52.340 --> 00:08:56.420 align:middle line:84% on materials that mankind has taken over millennia. 00:08:56.420 --> 00:09:00.680 align:middle line:84% Thermal gives you a framework for ingesting 00:09:00.680 --> 00:09:05.120 align:middle line:84% those observations and using them to make predictions 00:09:05.120 --> 00:09:07.540 align:middle line:84% about states that you have never seen before. 00:09:07.540 --> 00:09:09.260 align:middle line:84% So this is the way to think about it. 00:09:09.260 --> 00:09:18.620 align:middle line:84% Empirical observations-- so it's a bunch 00:09:18.620 --> 00:09:25.850 align:middle line:84% of observations, observation 1, observation 2, observation 3. 00:09:25.850 --> 00:09:31.610 align:middle line:84% All these little pieces of data, they 00:09:31.610 --> 00:09:35.970 align:middle line:84% get fed into something called the laws of thermodynamics. 00:09:35.970 --> 00:09:45.190 align:middle line:84% This is the conceptual framework. 00:09:45.190 --> 00:09:48.010 align:middle line:84% And then, from these observations 00:09:48.010 --> 00:09:50.320 align:middle line:84% and the laws of thermodynamics, you 00:09:50.320 --> 00:10:02.590 align:middle line:84% can deduce predictions, or what I like to call it, decisions. 00:10:02.590 --> 00:10:06.225 align:middle line:90% 00:10:06.225 --> 00:10:07.600 align:middle line:84% Because when we're scientists, we 00:10:07.600 --> 00:10:09.310 align:middle line:84% talk about hypotheses and predictions. 00:10:09.310 --> 00:10:12.970 align:middle line:84% But when we're engineers, we have to make a decision. 00:10:12.970 --> 00:10:14.950 align:middle line:84% What temperature will they run this furnace? 00:10:14.950 --> 00:10:20.720 align:middle line:84% How high can this autoclave run without ruining my product? 00:10:20.720 --> 00:10:23.240 align:middle line:84% What's the maximum temperature that this product 00:10:23.240 --> 00:10:25.520 align:middle line:90% can see during shipping? 00:10:25.520 --> 00:10:28.100 align:middle line:84% And you don't have time to run a million experiments. 00:10:28.100 --> 00:10:30.840 align:middle line:84% So you need a deductive framework to make decisions. 00:10:30.840 --> 00:10:32.930 align:middle line:84% And that's what thermo gives you. 00:10:32.930 --> 00:10:34.220 align:middle line:90% How do we store observations? 00:10:34.220 --> 00:10:35.660 align:middle line:90% We store them in databases. 00:10:35.660 --> 00:10:39.410 align:middle line:90% 00:10:39.410 --> 00:10:41.720 align:middle line:84% So as you'll see starting in the first piece, 00:10:41.720 --> 00:10:44.780 align:middle line:84% thermo concerns itself very much with the maintenance 00:10:44.780 --> 00:10:46.700 align:middle line:90% of databases. 00:10:46.700 --> 00:10:48.740 align:middle line:84% Without materials data, these laws of thermo 00:10:48.740 --> 00:10:49.930 align:middle line:90% are just text on a page. 00:10:49.930 --> 00:10:50.930 align:middle line:90% They're utterly useless. 00:10:50.930 --> 00:10:55.670 align:middle line:84% You need this-- the data fed into the deductive framework 00:10:55.670 --> 00:10:56.850 align:middle line:90% to make decisions. 00:10:56.850 --> 00:10:59.720 align:middle line:84% So the databases have huge economic value. 00:10:59.720 --> 00:11:03.560 align:middle line:84% When you download the student version of thermo calc, 00:11:03.560 --> 00:11:08.830 align:middle line:84% they're giving you a very minimal set of databases. 00:11:08.830 --> 00:11:10.840 align:middle line:84% First of all, you'd have to pay a fair amount 00:11:10.840 --> 00:11:11.870 align:middle line:90% to get a larger set. 00:11:11.870 --> 00:11:14.530 align:middle line:84% But if you want to get the real stuff, these are trade secrets. 00:11:14.530 --> 00:11:18.130 align:middle line:84% So companies like Alcoa, they guard 00:11:18.130 --> 00:11:21.820 align:middle line:84% their thermodynamic databases the way a company like Intel 00:11:21.820 --> 00:11:27.550 align:middle line:90% guards its lithography maps. 00:11:27.550 --> 00:11:30.890 align:middle line:84% It's like the key to the entire operation. 00:11:30.890 --> 00:11:34.270 align:middle line:84% So the economic value of data is huge in thermo 00:11:34.270 --> 00:11:37.840 align:middle line:84% and material science more generally. 00:11:37.840 --> 00:11:42.870 align:middle line:84% Now, fortunately, we don't need to sit down 00:11:42.870 --> 00:11:46.020 align:middle line:84% with our pen and paper and figure out 00:11:46.020 --> 00:11:49.230 align:middle line:84% what the law of thermodynamics predict every time. 00:11:49.230 --> 00:11:50.560 align:middle line:90% We have software for that. 00:11:50.560 --> 00:11:54.540 align:middle line:84% So databases fed into software allows you to make predictions 00:11:54.540 --> 00:11:58.110 align:middle line:84% and helps you make decisions in a reasonable time frame. 00:11:58.110 --> 00:12:00.735 align:middle line:84% That's how you'll use thermo in the real world. 00:12:00.735 --> 00:12:02.610 align:middle line:84% This is how you use thermo in the real world. 00:12:02.610 --> 00:12:12.590 align:middle line:90% 00:12:12.590 --> 00:12:18.870 align:middle line:84% OK, our next topic, systems in thermodynamics. 00:12:18.870 --> 00:12:33.370 align:middle line:90% 00:12:33.370 --> 00:12:36.880 align:middle line:84% All right, systems are characterized 00:12:36.880 --> 00:13:04.240 align:middle line:84% by temperature, pressure, volume, and composition, also 00:13:04.240 --> 00:13:05.050 align:middle line:90% boundaries. 00:13:05.050 --> 00:13:10.980 align:middle line:90% 00:13:10.980 --> 00:13:12.060 align:middle line:90% So here's an example. 00:13:12.060 --> 00:13:13.995 align:middle line:90% Here is a balloon. 00:13:13.995 --> 00:13:20.543 align:middle line:90% 00:13:20.543 --> 00:13:21.335 align:middle line:90% There's a boundary. 00:13:21.335 --> 00:13:25.610 align:middle line:90% 00:13:25.610 --> 00:13:27.170 align:middle line:90% This is in. 00:13:27.170 --> 00:13:29.670 align:middle line:90% And this is out. 00:13:29.670 --> 00:13:31.770 align:middle line:84% All right, so let's say we want to calculate 00:13:31.770 --> 00:13:35.470 align:middle line:84% some properties of the gas inside of this balloon. 00:13:35.470 --> 00:13:38.305 align:middle line:84% What should we take as the boundary of our system? 00:13:38.305 --> 00:13:43.817 align:middle line:90% 00:13:43.817 --> 00:13:45.400 align:middle line:84% It's kind of painfully obvious, right? 00:13:45.400 --> 00:13:48.767 align:middle line:90% 00:13:48.767 --> 00:13:50.180 align:middle line:90% You take the plastic. 00:13:50.180 --> 00:13:52.940 align:middle line:84% You take the actual balloon, the actual balloon that-- you 00:13:52.940 --> 00:13:54.148 align:middle line:90% choose that as your boundary. 00:13:54.148 --> 00:13:54.900 align:middle line:90% That makes sense. 00:13:54.900 --> 00:13:57.530 align:middle line:84% It's kind of obvious, but it's good to start 00:13:57.530 --> 00:13:59.480 align:middle line:90% from an obvious example. 00:13:59.480 --> 00:14:03.410 align:middle line:84% Why do you choose the physical balloon 00:14:03.410 --> 00:14:08.160 align:middle line:84% as a boundary of your system to analyze the gas inside? 00:14:08.160 --> 00:14:10.310 align:middle line:84% Why not just choose an arbitrary volume? 00:14:10.310 --> 00:14:14.450 align:middle line:84% Why not say no, I'm going to choose as my system 00:14:14.450 --> 00:14:15.830 align:middle line:90% the lower half of the balloon? 00:14:15.830 --> 00:14:21.372 align:middle line:84% And this is an imaginary line or surface separating 00:14:21.372 --> 00:14:22.580 align:middle line:90% the two parts of the balloon. 00:14:22.580 --> 00:14:27.742 align:middle line:84% Why not choose this lower volume to analyze? 00:14:27.742 --> 00:14:29.700 align:middle line:84% AUDIENCE: Because there's nothing separating it 00:14:29.700 --> 00:14:31.010 align:middle line:90% from the upper volume of gas. 00:14:31.010 --> 00:14:33.010 align:middle line:84% RAFAEL JARAMILLO: There's nothing separating it. 00:14:33.010 --> 00:14:35.950 align:middle line:84% And so as a result, particles can 00:14:35.950 --> 00:14:38.900 align:middle line:84% move between the lower volume and the upper volume. 00:14:38.900 --> 00:14:41.500 align:middle line:84% So if I choose the whole balloon, 00:14:41.500 --> 00:14:46.080 align:middle line:84% I get to use conservation of particle number. 00:14:46.080 --> 00:14:48.440 align:middle line:90% That's convenient. 00:14:48.440 --> 00:14:50.570 align:middle line:84% If I now treat these as two subsystems-- 00:14:50.570 --> 00:14:52.580 align:middle line:90% system A and system B-- 00:14:52.580 --> 00:14:56.770 align:middle line:84% now I need to keep track of how they exchange particles. 00:14:56.770 --> 00:14:59.410 align:middle line:90% It's more work. 00:14:59.410 --> 00:15:02.420 align:middle line:84% We get the same answer if you do it, but it's more work. 00:15:02.420 --> 00:15:05.440 align:middle line:84% So this is, again, a painfully obvious example. 00:15:05.440 --> 00:15:08.980 align:middle line:84% But starting as soon as this p set, 00:15:08.980 --> 00:15:11.140 align:middle line:84% we hope to make it-- give you some slightly less 00:15:11.140 --> 00:15:15.100 align:middle line:84% obvious examples, which is how you choose boundaries. 00:15:15.100 --> 00:15:19.190 align:middle line:84% You draw-- you choose boundaries-- boundaries chosen 00:15:19.190 --> 00:15:21.902 align:middle line:90% out of convenience. 00:15:21.902 --> 00:15:27.890 align:middle line:90% 00:15:27.890 --> 00:15:31.220 align:middle line:84% You choose a boundary when you analyze a system to make 00:15:31.220 --> 00:15:32.940 align:middle line:90% your life easier. 00:15:32.940 --> 00:15:35.895 align:middle line:84% It depends on what questions you're asking 00:15:35.895 --> 00:15:37.520 align:middle line:84% So I believe in problem 1 on the p set, 00:15:37.520 --> 00:15:39.937 align:middle line:84% we asked you to run through some of these mental exercises 00:15:39.937 --> 00:15:42.380 align:middle line:90% for different examples-- 00:15:42.380 --> 00:15:45.420 align:middle line:84% right, boundaries chosen out of convenience. 00:15:45.420 --> 00:15:48.050 align:middle line:90% So let's do an example. 00:15:48.050 --> 00:15:51.660 align:middle line:90% 00:15:51.660 --> 00:16:06.160 align:middle line:84% Example, adding sugar to a glass of water and stirring. 00:16:06.160 --> 00:16:10.800 align:middle line:90% 00:16:10.800 --> 00:16:13.492 align:middle line:90% So let's see. 00:16:13.492 --> 00:16:14.325 align:middle line:90% Let's draw a beaker. 00:16:14.325 --> 00:16:22.260 align:middle line:90% 00:16:22.260 --> 00:16:28.910 align:middle line:90% And there's water, good. 00:16:28.910 --> 00:16:31.360 align:middle line:90% And here's sugar. 00:16:31.360 --> 00:16:39.520 align:middle line:90% 00:16:39.520 --> 00:16:41.470 align:middle line:84% There's sugar, and the sugar gets added. 00:16:41.470 --> 00:16:45.585 align:middle line:90% 00:16:45.585 --> 00:16:46.960 align:middle line:84% And I'm going to have a stir bar. 00:16:46.960 --> 00:16:47.860 align:middle line:90% I have to stir. 00:16:47.860 --> 00:16:50.895 align:middle line:84% So I have a stir bar-- a little swizzle stick or something-- 00:16:50.895 --> 00:16:55.450 align:middle line:90% 00:16:55.450 --> 00:16:58.390 align:middle line:84% and stirring that around so it's moving. 00:16:58.390 --> 00:17:01.790 align:middle line:90% 00:17:01.790 --> 00:17:02.530 align:middle line:90% This is why. 00:17:02.530 --> 00:17:05.859 align:middle line:90% 00:17:05.859 --> 00:17:06.359 align:middle line:90% All right. 00:17:06.359 --> 00:17:09.857 align:middle line:90% 00:17:09.857 --> 00:17:11.065 align:middle line:90% Let's talk about this system. 00:17:11.065 --> 00:17:13.536 align:middle line:90% 00:17:13.536 --> 00:17:15.369 align:middle line:84% First, I'm going to write down a list of all 00:17:15.369 --> 00:17:17.300 align:middle line:90% the things in this picture. 00:17:17.300 --> 00:17:27.619 align:middle line:84% So the things are water, sugar, the glass, the atmosphere-- 00:17:27.619 --> 00:17:30.930 align:middle line:84% I didn't really draw it, but it's there-- 00:17:30.930 --> 00:17:32.730 align:middle line:84% and the stir stick and the stir bar. 00:17:32.730 --> 00:17:35.280 align:middle line:90% 00:17:35.280 --> 00:17:40.410 align:middle line:84% I want to get an answer like how sweet will the water become? 00:17:40.410 --> 00:17:42.180 align:middle line:90% That's the answer I need. 00:17:42.180 --> 00:17:44.968 align:middle line:84% What system-- so to analyze, what should be in the system, 00:17:44.968 --> 00:17:46.510 align:middle line:84% and what should not be in the system? 00:17:46.510 --> 00:17:50.330 align:middle line:84% So would somebody say should the water be in the system? 00:17:50.330 --> 00:17:52.880 align:middle line:84% AUDIENCE: Yes, because it's one of the main components 00:17:52.880 --> 00:17:53.687 align:middle line:90% of all the mixture. 00:17:53.687 --> 00:17:56.270 align:middle line:84% RAFAEL JARAMILLO: Yeah, OK, so we're going to choose the water 00:17:56.270 --> 00:17:57.712 align:middle line:90% and the sugar I will say also. 00:17:57.712 --> 00:17:59.670 align:middle line:84% It's one of the main components of the mixture. 00:17:59.670 --> 00:18:00.560 align:middle line:90% So let's go. 00:18:00.560 --> 00:18:01.775 align:middle line:90% What about the glass? 00:18:01.775 --> 00:18:03.830 align:middle line:84% Should that be part of the system? 00:18:03.830 --> 00:18:05.900 align:middle line:90% AUDIENCE: No. 00:18:05.900 --> 00:18:07.640 align:middle line:84% RAFAEL JARAMILLO: Probably not, unless we 00:18:07.640 --> 00:18:10.280 align:middle line:84% expect some kind of maybe reaction with the glass. 00:18:10.280 --> 00:18:14.690 align:middle line:84% But the sugar water, it's not going to etch the glass. 00:18:14.690 --> 00:18:16.440 align:middle line:84% If this were a hydrogen fluoride solution, 00:18:16.440 --> 00:18:17.130 align:middle line:90% it would etch the glass. 00:18:17.130 --> 00:18:18.090 align:middle line:90% We'd have to include the glass. 00:18:18.090 --> 00:18:19.798 align:middle line:84% But we're not going to include the glass. 00:18:19.798 --> 00:18:23.710 align:middle line:84% The atmosphere-- do we have to include that? 00:18:23.710 --> 00:18:25.750 align:middle line:84% AUDIENCE: No, because it's not changing. 00:18:25.750 --> 00:18:27.880 align:middle line:84% RAFAEL JARAMILLO: Yeah, if this is just 00:18:27.880 --> 00:18:30.280 align:middle line:84% something you're doing in your kitchen, probably not. 00:18:30.280 --> 00:18:34.630 align:middle line:84% If you're running a factory making sugar water, 00:18:34.630 --> 00:18:36.005 align:middle line:84% like a simple syrup or something, 00:18:36.005 --> 00:18:38.505 align:middle line:84% you probably want to include the atmosphere because you want 00:18:38.505 --> 00:18:39.880 align:middle line:90% really good process control. 00:18:39.880 --> 00:18:41.530 align:middle line:84% And the humidity in the atmosphere 00:18:41.530 --> 00:18:42.710 align:middle line:90% might make a difference. 00:18:42.710 --> 00:18:43.630 align:middle line:90% That's an example. 00:18:43.630 --> 00:18:50.590 align:middle line:84% Or if you're a monk brewing a farmhouse ale-- 00:18:50.590 --> 00:18:53.260 align:middle line:84% and we know that the stuff in the air from the surrounding 00:18:53.260 --> 00:18:55.833 align:middle line:84% farms makes it into the beer and helps change. 00:18:55.833 --> 00:18:57.250 align:middle line:84% So there are examples where you do 00:18:57.250 --> 00:18:59.708 align:middle line:84% want to include the atmosphere in the system, but here not. 00:18:59.708 --> 00:19:00.732 align:middle line:90% And the stir bar, not-- 00:19:00.732 --> 00:19:02.440 align:middle line:84% the stir bar has a function, but it's not 00:19:02.440 --> 00:19:05.640 align:middle line:84% going to be a part of the thermodynamic system. 00:19:05.640 --> 00:19:06.990 align:middle line:90% What about the boundaries? 00:19:06.990 --> 00:19:09.690 align:middle line:90% 00:19:09.690 --> 00:19:12.960 align:middle line:84% All right, these are the types of boundaries. 00:19:12.960 --> 00:19:33.620 align:middle line:90% 00:19:33.620 --> 00:19:35.420 align:middle line:84% And before we go through these, this 00:19:35.420 --> 00:19:39.050 align:middle line:84% is as good a time as any to remind you that the associated 00:19:39.050 --> 00:19:41.592 align:middle line:84% reading is every bit as much a part 00:19:41.592 --> 00:19:42.800 align:middle line:90% of the course as the lecture. 00:19:42.800 --> 00:19:44.690 align:middle line:84% So if you keep up with the reading 00:19:44.690 --> 00:19:47.570 align:middle line:84% and do the associated reading before lecture, 00:19:47.570 --> 00:19:50.375 align:middle line:84% you'll get a lot more out of the entire experience. 00:19:50.375 --> 00:19:52.250 align:middle line:84% So thank you for keeping up with the reading. 00:19:52.250 --> 00:19:55.280 align:middle line:84% All right, boundaries-- open or closed? 00:19:55.280 --> 00:19:56.930 align:middle line:90% Somebody please tell me. 00:19:56.930 --> 00:19:58.190 align:middle line:90% Is this open or closed system? 00:19:58.190 --> 00:20:01.850 align:middle line:90% Which would you choose and why? 00:20:01.850 --> 00:20:04.610 align:middle line:84% And what does that mean, open or closed? 00:20:04.610 --> 00:20:07.070 align:middle line:90% Somebody. 00:20:07.070 --> 00:20:09.860 align:middle line:84% AUDIENCE: I would say it was closed because nothing 00:20:09.860 --> 00:20:11.240 align:middle line:90% is leaving the system. 00:20:11.240 --> 00:20:14.180 align:middle line:84% There's no evaporation happening or particles leaving. 00:20:14.180 --> 00:20:16.790 align:middle line:84% RAFAEL JARAMILLO: Good, OK, that's what I would choose too. 00:20:16.790 --> 00:20:19.310 align:middle line:84% Closed means no loss of particles 00:20:19.310 --> 00:20:20.990 align:middle line:90% or no gain of particles. 00:20:20.990 --> 00:20:22.770 align:middle line:84% Particle number remains the same. 00:20:22.770 --> 00:20:25.640 align:middle line:84% So the example given there was that if you 00:20:25.640 --> 00:20:27.320 align:middle line:90% included evaporation-- 00:20:27.320 --> 00:20:31.483 align:middle line:84% loss of water-- it would be an open system. 00:20:31.483 --> 00:20:33.650 align:middle line:84% You'd have to include the atmosphere in your system. 00:20:33.650 --> 00:20:36.362 align:middle line:90% 00:20:36.362 --> 00:20:38.570 align:middle line:84% And if you're growing-- if you're in a crystal growth 00:20:38.570 --> 00:20:43.460 align:middle line:84% experiment where you slowly let the water evaporate-- 00:20:43.460 --> 00:20:48.178 align:middle line:84% the supernatant-- then it's an open system. 00:20:48.178 --> 00:20:50.220 align:middle line:84% But we're doing this quickly, and we're not going 00:20:50.220 --> 00:20:51.428 align:middle line:90% to wait for water evaporates. 00:20:51.428 --> 00:20:52.470 align:middle line:90% So closed, thank you. 00:20:52.470 --> 00:20:56.590 align:middle line:90% All right, rigid or not rigid? 00:20:56.590 --> 00:21:00.190 align:middle line:84% AUDIENCE: Maybe not rigid since the top is, 00:21:00.190 --> 00:21:04.520 align:middle line:84% like not like a hard solid surface. 00:21:04.520 --> 00:21:05.720 align:middle line:90% RAFAEL JARAMILLO: OK, good. 00:21:05.720 --> 00:21:08.000 align:middle line:90% So the top, it's not rigid. 00:21:08.000 --> 00:21:11.400 align:middle line:84% That's what I would choose too Let's talk a little bit more 00:21:11.400 --> 00:21:13.720 align:middle line:90% about what that means. 00:21:13.720 --> 00:21:16.380 align:middle line:84% It means that the volume can change. 00:21:16.380 --> 00:21:17.955 align:middle line:90% The volume is free to change. 00:21:17.955 --> 00:21:19.080 align:middle line:90% That's what was said there. 00:21:19.080 --> 00:21:21.130 align:middle line:90% The top is not a hard surface. 00:21:21.130 --> 00:21:24.220 align:middle line:84% So we assume that the walls of the glass are rigid. 00:21:24.220 --> 00:21:25.630 align:middle line:90% They're not going to change. 00:21:25.630 --> 00:21:28.680 align:middle line:84% But the top surface is what's called a free surface. 00:21:28.680 --> 00:21:32.930 align:middle line:84% It can exchange volume with the atmosphere. 00:21:32.930 --> 00:21:36.540 align:middle line:84% And the ability to exchange volume-- 00:21:36.540 --> 00:21:38.580 align:middle line:84% that's the mechanism by which two systems 00:21:38.580 --> 00:21:40.630 align:middle line:90% arrive at the same pressure. 00:21:40.630 --> 00:21:42.990 align:middle line:84% So there's notion of pressure regulation. 00:21:42.990 --> 00:21:47.920 align:middle line:84% Temperature regulation becomes very important in thermo. 00:21:47.920 --> 00:21:52.090 align:middle line:84% Non rigid systems are pressure regulated 00:21:52.090 --> 00:21:54.430 align:middle line:84% because they can exchange volume with the atmosphere. 00:21:54.430 --> 00:21:56.920 align:middle line:84% If there is a fluctuation in atmospheric pressure, 00:21:56.920 --> 00:21:59.350 align:middle line:84% that same temperature-- the same pressure fluctuation 00:21:59.350 --> 00:22:03.440 align:middle line:84% will be felt by the water bath, for instance. 00:22:03.440 --> 00:22:06.020 align:middle line:84% As opposed to a rigid system, a rigid system 00:22:06.020 --> 00:22:07.010 align:middle line:90% can build pressure. 00:22:07.010 --> 00:22:09.410 align:middle line:84% You can have a bomb or a high pressure vessel. 00:22:09.410 --> 00:22:11.460 align:middle line:84% That's a different pressure from the outside. 00:22:11.460 --> 00:22:11.960 align:middle line:90% Why? 00:22:11.960 --> 00:22:13.813 align:middle line:84% Because it's fixed volume, rigid. 00:22:13.813 --> 00:22:14.480 align:middle line:90% All right, good. 00:22:14.480 --> 00:22:17.150 align:middle line:84% And finally, adiabatic or diathermal? 00:22:17.150 --> 00:22:26.502 align:middle line:90% 00:22:26.502 --> 00:22:28.210 align:middle line:84% Right, so the non rigid meant that you're 00:22:28.210 --> 00:22:32.450 align:middle line:84% going to be at atmospheric pressure throughout. 00:22:32.450 --> 00:22:37.310 align:middle line:84% In my view, the Zoom video camera webcam review 00:22:37.310 --> 00:22:40.850 align:middle line:84% is blocking this text right here. 00:22:40.850 --> 00:22:43.940 align:middle line:84% Is it blocking this text in anyone else's view? 00:22:43.940 --> 00:22:44.850 align:middle line:90% AUDIENCE: No. 00:22:44.850 --> 00:22:45.260 align:middle line:90% RAFAEL JARAMILLO: OK, good. 00:22:45.260 --> 00:22:45.760 align:middle line:90% Thanks. 00:22:45.760 --> 00:22:47.930 align:middle line:84% All right, so what about adiabatic or diathermal? 00:22:47.930 --> 00:22:50.481 align:middle line:84% Is this adiabatic, or is it diathermal? 00:22:50.481 --> 00:22:56.170 align:middle line:84% The boundaries-- adiabatic or diathermal? 00:22:56.170 --> 00:23:00.010 align:middle line:84% So adiabatic means a process or a boundary 00:23:00.010 --> 00:23:03.190 align:middle line:90% that does not allow heating-- 00:23:03.190 --> 00:23:05.260 align:middle line:84% so a thermally insulating battery. 00:23:05.260 --> 00:23:08.805 align:middle line:90% 00:23:08.805 --> 00:23:09.930 align:middle line:90% Diathermal is the opposite. 00:23:09.930 --> 00:23:12.660 align:middle line:84% Diathermal thermal is a process or a boundary 00:23:12.660 --> 00:23:16.740 align:middle line:84% that allows heating, allows heat to flow, allows heat exchange. 00:23:16.740 --> 00:23:18.210 align:middle line:90% AUDIENCE: So it'd be diathermal. 00:23:18.210 --> 00:23:20.043 align:middle line:84% RAFAEL JARAMILLO: It'd be diathermal, right. 00:23:20.043 --> 00:23:27.940 align:middle line:84% So in the same way that the free surface allows the atmosphere 00:23:27.940 --> 00:23:30.160 align:middle line:84% to regulate the pressure in the water, 00:23:30.160 --> 00:23:32.140 align:middle line:84% keeping it at atmospheric pressure 00:23:32.140 --> 00:23:37.220 align:middle line:84% throughout, the diathermal boundaries in glass 00:23:37.220 --> 00:23:38.667 align:middle line:90% might be a little slow-- 00:23:38.667 --> 00:23:40.250 align:middle line:84% slow thermal transport, but definitely 00:23:40.250 --> 00:23:43.070 align:middle line:84% have a very fast thermal transport there at the surface. 00:23:43.070 --> 00:23:47.278 align:middle line:84% This is going to keep temperature 00:23:47.278 --> 00:23:49.070 align:middle line:84% of the room-- this is the temperature there 00:23:49.070 --> 00:23:50.483 align:middle line:90% the room throughout. 00:23:50.483 --> 00:23:54.433 align:middle line:90% 00:23:54.433 --> 00:23:55.850 align:middle line:84% So the diathermal thermal boundary 00:23:55.850 --> 00:23:57.170 align:middle line:90% regulates the temperature. 00:23:57.170 --> 00:23:59.855 align:middle line:84% The non rigid boundary regulates the pressure. 00:23:59.855 --> 00:24:03.160 align:middle line:90% 00:24:03.160 --> 00:24:05.705 align:middle line:84% I'm taking my time here, intentionally introducing 00:24:05.705 --> 00:24:06.580 align:middle line:90% a bunch of new terms. 00:24:06.580 --> 00:24:11.110 align:middle line:84% Or if they're not new terms, the meaning of all these terms 00:24:11.110 --> 00:24:14.320 align:middle line:84% is very specific in thermo, so the idea of regulation, 00:24:14.320 --> 00:24:15.760 align:middle line:90% the idea of choosing boundaries. 00:24:15.760 --> 00:24:19.540 align:middle line:90% 00:24:19.540 --> 00:24:22.690 align:middle line:84% So you'll do some examples like this in the p set. 00:24:22.690 --> 00:24:25.825 align:middle line:90% 00:24:25.825 --> 00:24:27.700 align:middle line:84% All right, let's talk about types of systems, 00:24:27.700 --> 00:24:28.533 align:middle line:90% classifying systems. 00:24:28.533 --> 00:24:36.180 align:middle line:90% 00:24:36.180 --> 00:24:37.260 align:middle line:90% Classifications. 00:24:37.260 --> 00:24:43.940 align:middle line:90% 00:24:43.940 --> 00:24:46.040 align:middle line:84% All right, so this is just getting some essentials 00:24:46.040 --> 00:24:47.270 align:middle line:90% out of the way here-- 00:24:47.270 --> 00:24:53.471 align:middle line:90% unary, one component. 00:24:53.471 --> 00:24:57.620 align:middle line:90% 00:24:57.620 --> 00:25:00.955 align:middle line:84% All right, so an example of a component would be water. 00:25:00.955 --> 00:25:27.940 align:middle line:90% 00:25:27.940 --> 00:25:29.050 align:middle line:90% OK, so here's an example. 00:25:29.050 --> 00:25:30.950 align:middle line:84% A unary system has one component, 00:25:30.950 --> 00:25:33.460 align:middle line:90% one molecular component. 00:25:33.460 --> 00:25:35.290 align:middle line:84% A multi component system has more than one. 00:25:35.290 --> 00:25:38.830 align:middle line:84% So, for example, the binary system of water and sugar. 00:25:38.830 --> 00:25:43.820 align:middle line:90% 00:25:43.820 --> 00:25:45.820 align:middle line:84% I've got hydrogen, oxygen, and carbon here. 00:25:45.820 --> 00:25:47.590 align:middle line:84% How come it's not three components? 00:25:47.590 --> 00:25:48.190 align:middle line:90% Anybody? 00:25:48.190 --> 00:25:52.252 align:middle line:90% 00:25:52.252 --> 00:25:54.460 align:middle line:84% AUDIENCE: Because at no point are we discussing like, 00:25:54.460 --> 00:25:56.858 align:middle line:84% the separation of those components. 00:25:56.858 --> 00:25:58.150 align:middle line:90% RAFAEL JARAMILLO: That's right. 00:25:58.150 --> 00:26:02.260 align:middle line:84% At no point are we breaking bonds or in reforming 00:26:02.260 --> 00:26:02.800 align:middle line:90% molecules. 00:26:02.800 --> 00:26:04.490 align:middle line:84% This is remaining water throughout. 00:26:04.490 --> 00:26:07.870 align:middle line:84% This is remaining sucrose throughout. 00:26:07.870 --> 00:26:11.480 align:middle line:84% This is not a digestive system, and you break down the sugar. 00:26:11.480 --> 00:26:14.170 align:middle line:84% This is not an electrochemical water-splitting system 00:26:14.170 --> 00:26:18.280 align:middle line:84% where you might be using some source of energy 00:26:18.280 --> 00:26:22.480 align:middle line:84% to electrochemically generate hydrogen gas from water. 00:26:22.480 --> 00:26:23.950 align:middle line:90% So that's good. 00:26:23.950 --> 00:26:27.600 align:middle line:84% So your choice of unary, multi component-- 00:26:27.600 --> 00:26:30.090 align:middle line:84% there can be more than one answer. 00:26:30.090 --> 00:26:32.880 align:middle line:84% And the same molecular components 00:26:32.880 --> 00:26:35.890 align:middle line:84% can be analyzed as unary, or a multi component system, 00:26:35.890 --> 00:26:37.930 align:middle line:90% depending on the situation. 00:26:37.930 --> 00:26:40.643 align:middle line:84% So, again, you make these decisions out of convenience 00:26:40.643 --> 00:26:42.060 align:middle line:84% because you understand the process 00:26:42.060 --> 00:26:44.810 align:middle line:84% that you're engineering, that you're designing. 00:26:44.810 --> 00:26:50.940 align:middle line:84% All right, OK, good, so that's urinary versus multi component. 00:26:50.940 --> 00:26:52.815 align:middle line:84% And this kind of gets-- sometimes 00:26:52.815 --> 00:26:55.770 align:middle line:84% can get a little bit easy to get tripped up there. 00:26:55.770 --> 00:27:03.170 align:middle line:84% All right, two different types of classification-- homogeneous 00:27:03.170 --> 00:27:05.090 align:middle line:90% first, heterogeneous. 00:27:05.090 --> 00:27:09.280 align:middle line:90% 00:27:09.280 --> 00:27:11.050 align:middle line:90% So homogeneous means one phase. 00:27:11.050 --> 00:27:15.200 align:middle line:90% 00:27:15.200 --> 00:27:20.210 align:middle line:84% So, for example, sodium acetate-- 00:27:20.210 --> 00:27:28.090 align:middle line:90% 00:27:28.090 --> 00:27:29.530 align:middle line:90% the sodium acetate solution. 00:27:29.530 --> 00:27:34.600 align:middle line:84% That was-- the supersaturated sodium acetate solution 00:27:34.600 --> 00:27:39.380 align:middle line:84% was a starting point for the incident 00:27:39.380 --> 00:27:42.840 align:middle line:84% and hot plate, sodium acetate solution. 00:27:42.840 --> 00:27:45.160 align:middle line:90% What about heterogeneous? 00:27:45.160 --> 00:27:59.270 align:middle line:84% More than one phase, right-- solution plus solid, 00:27:59.270 --> 00:28:00.811 align:middle line:90% sodium acetate. 00:28:00.811 --> 00:28:04.740 align:middle line:90% 00:28:04.740 --> 00:28:12.160 align:middle line:84% So that's-- because I think a little bit less description. 00:28:12.160 --> 00:28:13.570 align:middle line:90% What about closed versus open? 00:28:13.570 --> 00:28:22.130 align:middle line:90% 00:28:22.130 --> 00:28:23.990 align:middle line:90% This we've already discussed-- 00:28:23.990 --> 00:28:45.490 align:middle line:84% no mass exchange with surroundings versus 00:28:45.490 --> 00:28:47.260 align:middle line:84% can exchange mass with surroundings. 00:28:47.260 --> 00:28:54.580 align:middle line:90% 00:28:54.580 --> 00:28:57.310 align:middle line:84% So those are some basic and important classifications. 00:28:57.310 --> 00:29:01.810 align:middle line:90% 00:29:01.810 --> 00:29:05.260 align:middle line:84% Next category-- we're going through the necessary stuff 00:29:05.260 --> 00:29:08.530 align:middle line:84% here to get started on real thermal problems. 00:29:08.530 --> 00:29:14.240 align:middle line:84% State functions or, if you like, variables. 00:29:14.240 --> 00:29:19.470 align:middle line:84% We'll use these interchangeably, state functions and state 00:29:19.470 --> 00:29:20.405 align:middle line:90% variables. 00:29:20.405 --> 00:29:21.780 align:middle line:84% So these characterize the system. 00:29:21.780 --> 00:29:35.240 align:middle line:90% 00:29:35.240 --> 00:29:36.890 align:middle line:90% They are independent of history. 00:29:36.890 --> 00:29:47.110 align:middle line:90% 00:29:47.110 --> 00:29:51.250 align:middle line:90% This is a really subtle point. 00:29:51.250 --> 00:29:52.180 align:middle line:90% This will trip you up. 00:29:52.180 --> 00:29:53.830 align:middle line:90% It trips me up. 00:29:53.830 --> 00:29:56.610 align:middle line:90% It seems obvious, right. 00:29:56.610 --> 00:29:59.430 align:middle line:84% The fact that you could characterize a system 00:29:59.430 --> 00:30:01.680 align:middle line:84% with variables which are independent of the history 00:30:01.680 --> 00:30:04.560 align:middle line:84% of that system is very non obvious. 00:30:04.560 --> 00:30:07.860 align:middle line:84% That was a major intellectual accomplishment. 00:30:07.860 --> 00:30:10.050 align:middle line:84% It shouldn't sit easily with you. 00:30:10.050 --> 00:30:11.520 align:middle line:90% That takes some getting used to. 00:30:11.520 --> 00:30:13.050 align:middle line:84% You shouldn't trust me on this yet. 00:30:13.050 --> 00:30:16.240 align:middle line:90% 00:30:16.240 --> 00:30:31.580 align:middle line:84% Common state functions found in 020-- 00:30:31.580 --> 00:30:36.350 align:middle line:84% so would somebody like to volunteer a state function, 00:30:36.350 --> 00:30:39.630 align:middle line:84% a common state function you might find in thermo? 00:30:39.630 --> 00:30:40.560 align:middle line:90% AUDIENCE: Temperature 00:30:40.560 --> 00:30:41.768 align:middle line:90% RAFAEL JARAMILLO: Yeah, temp. 00:30:41.768 --> 00:30:44.310 align:middle line:90% So that's a state function. 00:30:44.310 --> 00:30:46.415 align:middle line:90% We use t. 00:30:46.415 --> 00:30:56.360 align:middle line:84% To denote volume, we use v. Pressure is p. 00:30:56.360 --> 00:30:59.280 align:middle line:90% Any others? 00:30:59.280 --> 00:31:01.168 align:middle line:90% AUDIENCE: Enthalpy. 00:31:01.168 --> 00:31:02.460 align:middle line:90% RAFAEL JARAMILLO: Enthalpy, OK. 00:31:02.460 --> 00:31:03.460 align:middle line:90% That's a state function. 00:31:03.460 --> 00:31:11.070 align:middle line:90% 00:31:11.070 --> 00:31:15.360 align:middle line:84% What about one that's not so specific in thermo? 00:31:15.360 --> 00:31:18.600 align:middle line:84% Are there others that are more colloquial? 00:31:18.600 --> 00:31:19.620 align:middle line:90% AUDIENCE: Concentration. 00:31:19.620 --> 00:31:21.870 align:middle line:84% RAFAEL JARAMILLO: Concentration, I'll say composition. 00:31:21.870 --> 00:31:31.420 align:middle line:84% Yeah, composition-- and we'll use atomic percent often 00:31:31.420 --> 00:31:33.460 align:middle line:90% in this class. 00:31:33.460 --> 00:31:42.647 align:middle line:84% What about mole number, total system size, like that? 00:31:42.647 --> 00:31:43.730 align:middle line:90% And then there's enthalpy. 00:31:43.730 --> 00:31:47.920 align:middle line:84% And then there are others which are more 00:31:47.920 --> 00:31:49.270 align:middle line:90% specific to thermodynamics. 00:31:49.270 --> 00:31:51.022 align:middle line:90% There's entropy. 00:31:51.022 --> 00:31:52.105 align:middle line:90% There's Gibbs free energy. 00:31:52.105 --> 00:31:59.030 align:middle line:90% 00:31:59.030 --> 00:32:00.500 align:middle line:84% And there's Helmholtz free energy. 00:32:00.500 --> 00:32:14.510 align:middle line:90% 00:32:14.510 --> 00:32:15.800 align:middle line:90% If we were course 2-- 00:32:15.800 --> 00:32:18.500 align:middle line:84% if we were mechanical engineers-- 00:32:18.500 --> 00:32:27.480 align:middle line:84% we would be spending a lot more time on Helmholtz free energy 00:32:27.480 --> 00:32:30.140 align:middle line:90% and enthalpy. 00:32:30.140 --> 00:32:31.880 align:middle line:84% If we were physicists, we'd be spending 00:32:31.880 --> 00:32:34.680 align:middle line:84% a lot more time on Helmholtz free energy 00:32:34.680 --> 00:32:42.160 align:middle line:84% and energy, which we're going to use u for internal energy. 00:32:42.160 --> 00:32:43.840 align:middle line:84% But as material scientists, we spend 00:32:43.840 --> 00:32:49.330 align:middle line:84% most of our time on Gibbs free energy and enthalpy for reasons 00:32:49.330 --> 00:32:52.900 align:middle line:84% that we'll discuss at length in a couple of lectures. 00:32:52.900 --> 00:32:53.770 align:middle line:90% But there are more. 00:32:53.770 --> 00:32:55.270 align:middle line:90% There are more. 00:32:55.270 --> 00:32:59.710 align:middle line:84% Like magnetization, that's one we don't-- that electric 00:32:59.710 --> 00:33:01.240 align:middle line:90% polarization. 00:33:01.240 --> 00:33:01.870 align:middle line:90% There're many. 00:33:01.870 --> 00:33:08.068 align:middle line:90% 00:33:08.068 --> 00:33:09.360 align:middle line:90% OK, so we have state functions. 00:33:09.360 --> 00:33:10.780 align:middle line:90% We have state variables. 00:33:10.780 --> 00:33:12.630 align:middle line:90% We also have equations of state. 00:33:12.630 --> 00:33:20.690 align:middle line:90% 00:33:20.690 --> 00:33:22.760 align:middle line:84% So an equation of state, in general, 00:33:22.760 --> 00:33:27.940 align:middle line:84% is some state function X equals a function of other state 00:33:27.940 --> 00:33:32.695 align:middle line:90% functions Y1, Y2, Y3. 00:33:32.695 --> 00:33:35.350 align:middle line:90% 00:33:35.350 --> 00:33:42.100 align:middle line:84% And in this formulism, that's a state function. 00:33:42.100 --> 00:33:46.250 align:middle line:90% And these are state variables. 00:33:46.250 --> 00:33:48.770 align:middle line:84% But I'm going to use this interchangeably-- state 00:33:48.770 --> 00:33:50.420 align:middle line:90% functions, state variables. 00:33:50.420 --> 00:33:54.282 align:middle line:84% All right, so you all know one state function. 00:33:54.282 --> 00:33:55.740 align:middle line:84% What's the state function everybody 00:33:55.740 --> 00:33:56.907 align:middle line:90% knows, even on the T-shirts? 00:33:56.907 --> 00:34:00.525 align:middle line:90% 00:34:00.525 --> 00:34:01.900 align:middle line:84% When I do this lecture in person, 00:34:01.900 --> 00:34:05.100 align:middle line:84% I wear my MIT T-shirt with a state function on it. 00:34:05.100 --> 00:34:08.440 align:middle line:90% 00:34:08.440 --> 00:34:09.699 align:middle line:90% AUDIENCE: It'd be PV=nRT. 00:34:09.699 --> 00:34:11.290 align:middle line:84% RAFAEL JARAMILLO: Yeah, PV=nRT, right. 00:34:11.290 --> 00:34:15.989 align:middle line:90% PV equals nRT. 00:34:15.989 --> 00:34:18.310 align:middle line:90% OK, so that's a state function. 00:34:18.310 --> 00:34:20.469 align:middle line:84% That's a state function for an ideal gas. 00:34:20.469 --> 00:34:24.760 align:middle line:84% This is true always for an ideal gas at equilibrium. 00:34:24.760 --> 00:34:28.675 align:middle line:84% That's pretty cool, and you can do a lot with that. 00:34:28.675 --> 00:34:30.050 align:middle line:84% But before we do a lot with that, 00:34:30.050 --> 00:34:34.409 align:middle line:84% I want to warn you this is the exception rather than the rule. 00:34:34.409 --> 00:34:37.530 align:middle line:84% For almost every system, every material 00:34:37.530 --> 00:34:39.120 align:middle line:84% which you'll use in your careers, 00:34:39.120 --> 00:34:42.989 align:middle line:84% we do not have a state function like this. 00:34:42.989 --> 00:34:46.960 align:middle line:84% Maybe we have some that are empirically determined. 00:34:46.960 --> 00:34:49.780 align:middle line:84% You might find some magnetic systems for which state 00:34:49.780 --> 00:34:51.550 align:middle line:84% functions have been exactly derived 00:34:51.550 --> 00:34:54.642 align:middle line:84% from fundamental principles like this one. 00:34:54.642 --> 00:34:56.600 align:middle line:84% But this is the exception rather than the rule. 00:34:56.600 --> 00:34:59.440 align:middle line:84% Usually, you can't write down a closed form like this. 00:34:59.440 --> 00:35:04.240 align:middle line:84% Usually, you have to deal with much more complicated data 00:35:04.240 --> 00:35:05.050 align:middle line:90% resources. 00:35:05.050 --> 00:35:08.770 align:middle line:90% 00:35:08.770 --> 00:35:10.690 align:middle line:90% Something on units here-- 00:35:10.690 --> 00:35:12.460 align:middle line:90% try to sneak this in. 00:35:12.460 --> 00:35:17.910 align:middle line:90% R equals PV over nT. 00:35:17.910 --> 00:35:21.210 align:middle line:90% What are the units of that? 00:35:21.210 --> 00:35:24.930 align:middle line:90% Pressure is Pascals. 00:35:24.930 --> 00:35:27.930 align:middle line:90% Volume is meters cubed-- 00:35:27.930 --> 00:35:31.270 align:middle line:84% make this so that it looks like Pascals. 00:35:31.270 --> 00:35:33.817 align:middle line:90% Mole is unitless, just a number. 00:35:33.817 --> 00:35:34.900 align:middle line:90% And temperature is Kelvin. 00:35:34.900 --> 00:35:37.500 align:middle line:90% 00:35:37.500 --> 00:35:40.050 align:middle line:84% In fundamental SI units, a Pascal 00:35:40.050 --> 00:35:42.360 align:middle line:90% is a Newton per meter squared. 00:35:42.360 --> 00:35:45.180 align:middle line:84% Force over area, that's pressure. 00:35:45.180 --> 00:35:49.670 align:middle line:84% We have a meter cubed, and we have a Kelvin. 00:35:49.670 --> 00:35:54.500 align:middle line:84% So then, you get Newton meter by-- 00:35:54.500 --> 00:35:58.310 align:middle line:84% and what's a force displaced over a meter, Newton meter? 00:35:58.310 --> 00:36:01.650 align:middle line:90% 00:36:01.650 --> 00:36:03.780 align:middle line:90% AUDIENCE: The joule. 00:36:03.780 --> 00:36:05.610 align:middle line:84% RAFAEL JARAMILLO: Joule, joule Kelvin. 00:36:05.610 --> 00:36:11.833 align:middle line:84% So R equals 8.314 joules per Kelvin. 00:36:11.833 --> 00:36:13.125 align:middle line:90% It's a handy thing to remember. 00:36:13.125 --> 00:36:16.253 align:middle line:90% 00:36:16.253 --> 00:36:18.420 align:middle line:84% We're going to be sticklers for units in this stuff. 00:36:18.420 --> 00:36:21.140 align:middle line:90% 00:36:21.140 --> 00:36:23.160 align:middle line:90% I was going to say more things-- 00:36:23.160 --> 00:36:24.510 align:middle line:90% thermodynamic properties. 00:36:24.510 --> 00:36:36.420 align:middle line:90% 00:36:36.420 --> 00:36:37.920 align:middle line:84% All right, so at the very beginning, 00:36:37.920 --> 00:36:41.960 align:middle line:84% I told you that states of matter had certain responses 00:36:41.960 --> 00:36:45.860 align:middle line:84% when you squeeze them or you added stuff or you heated them. 00:36:45.860 --> 00:36:54.100 align:middle line:84% And these are going to be described 00:36:54.100 --> 00:36:56.750 align:middle line:84% by thermodynamic response functions. 00:36:56.750 --> 00:36:59.650 align:middle line:84% So that response function term sounds kind of fancy. 00:36:59.650 --> 00:37:00.820 align:middle line:90% Don't let it scare you. 00:37:00.820 --> 00:37:03.700 align:middle line:84% It describes how a system responds to something. 00:37:03.700 --> 00:37:05.670 align:middle line:84% So someone screams, you cover your ear. 00:37:05.670 --> 00:37:07.520 align:middle line:90% That's your response function. 00:37:07.520 --> 00:37:12.330 align:middle line:84% So some common response functions that we use in thermo 00:37:12.330 --> 00:37:25.460 align:middle line:84% are compressibility, isothermal compressibility, a fixed 00:37:25.460 --> 00:37:26.546 align:middle line:90% temperature. 00:37:26.546 --> 00:37:31.110 align:middle line:90% 00:37:31.110 --> 00:37:34.560 align:middle line:84% And, of course, this is the same as d log V dP. 00:37:34.560 --> 00:37:35.640 align:middle line:90% So you see this a lot. 00:37:35.640 --> 00:37:42.400 align:middle line:90% 00:37:42.400 --> 00:37:44.860 align:middle line:84% The only real prerequisite for thermo 00:37:44.860 --> 00:37:47.517 align:middle line:90% is multivariable calculus. 00:37:47.517 --> 00:37:49.850 align:middle line:84% And I think the first time I learned thermo and probably 00:37:49.850 --> 00:37:52.580 align:middle line:84% a second time even, I didn't appreciate 00:37:52.580 --> 00:37:55.760 align:middle line:84% just how much I relied on multivariable calculus. 00:37:55.760 --> 00:37:58.550 align:middle line:84% So just know that now so that you're not surprised later. 00:37:58.550 --> 00:38:01.350 align:middle line:90% 00:38:01.350 --> 00:38:03.610 align:middle line:90% All right, thermal expansion-- 00:38:03.610 --> 00:38:04.690 align:middle line:90% it's another common one. 00:38:04.690 --> 00:38:10.550 align:middle line:90% 00:38:10.550 --> 00:38:13.340 align:middle line:84% Alpha equals-- again, we're going 00:38:13.340 --> 00:38:18.250 align:middle line:90% to make this volume independent. 00:38:18.250 --> 00:38:22.490 align:middle line:90% 00:38:22.490 --> 00:38:24.580 align:middle line:84% And we're going to do that at fixed pressure. 00:38:24.580 --> 00:38:32.910 align:middle line:90% 00:38:32.910 --> 00:38:37.910 align:middle line:84% And there are others, but these are the easiest ones 00:38:37.910 --> 00:38:40.190 align:middle line:90% to write down. 00:38:40.190 --> 00:38:43.152 align:middle line:84% I'm giving you an idea of the sorts of properties that we're 00:38:43.152 --> 00:38:44.360 align:middle line:90% going to calculate in thermo. 00:38:44.360 --> 00:38:59.126 align:middle line:84% So let's consider ideal gas compression at fixed temp-- 00:38:59.126 --> 00:39:05.400 align:middle line:90% 00:39:05.400 --> 00:39:09.000 align:middle line:84% volume initial at pressure initial 00:39:09.000 --> 00:39:14.080 align:middle line:84% going to volume final at pressure final. 00:39:14.080 --> 00:39:20.390 align:middle line:84% All right, so compressibility Bose minus 1 over V dV 00:39:20.390 --> 00:39:23.870 align:middle line:90% dP at fixed temperature. 00:39:23.870 --> 00:39:28.000 align:middle line:84% And for an ideal gas, this is very, very simple. 00:39:28.000 --> 00:39:41.860 align:middle line:84% This is minus 1 over V dVP at fixed temperature nRT over P. 00:39:41.860 --> 00:39:48.780 align:middle line:90% This equals nRT over VP. 00:39:48.780 --> 00:39:55.870 align:middle line:84% 1 over P equals 1 over P. This is 00:39:55.870 --> 00:40:00.700 align:middle line:84% really simple for an ideal gas and only for an ideal gas. 00:40:00.700 --> 00:40:02.850 align:middle line:84% So the final volume after compression 00:40:02.850 --> 00:40:05.055 align:middle line:84% is going to be the initial volume plus the change. 00:40:05.055 --> 00:40:12.470 align:middle line:90% 00:40:12.470 --> 00:40:16.770 align:middle line:84% So it's like second fundamental theorem of calculus. 00:40:16.770 --> 00:40:18.050 align:middle line:90% So we're going to plug in-- 00:40:18.050 --> 00:40:26.060 align:middle line:90% 00:40:26.060 --> 00:40:27.380 align:middle line:90% what's the integrand? 00:40:27.380 --> 00:40:28.805 align:middle line:90% It's minus V beta. 00:40:28.805 --> 00:40:33.060 align:middle line:90% 00:40:33.060 --> 00:40:34.900 align:middle line:90% You continue to plug in. 00:40:34.900 --> 00:40:36.630 align:middle line:90% This is volume initial minus-- 00:40:36.630 --> 00:40:39.570 align:middle line:90% 00:40:39.570 --> 00:40:55.700 align:middle line:84% so hang on-- dP nRT over P. 1 over P equals V initial minus 00:40:55.700 --> 00:41:08.540 align:middle line:84% nRT P initial plus nRT P final, which, of course, just equals 00:41:08.540 --> 00:41:09.330 align:middle line:90% V final. 00:41:09.330 --> 00:41:11.900 align:middle line:84% So this calculation is really trivial for an ideal, guys. 00:41:11.900 --> 00:41:14.265 align:middle line:84% You get exactly what you think you would get. 00:41:14.265 --> 00:41:15.890 align:middle line:84% The reason why I took the time to do it 00:41:15.890 --> 00:41:22.350 align:middle line:84% is to show you the manipulations that you'll need to do later 00:41:22.350 --> 00:41:25.470 align:middle line:90% on for non ideal gasses. 00:41:25.470 --> 00:41:26.970 align:middle line:84% Now, thinking about this, you've got 00:41:26.970 --> 00:41:28.830 align:middle line:84% to put your multivariable calculus hat on. 00:41:28.830 --> 00:41:32.570 align:middle line:90% 00:41:32.570 --> 00:41:35.910 align:middle line:84% Of course, for an ideal gas we get this-- 00:41:35.910 --> 00:41:41.960 align:middle line:90% 1 over x, these relationships-- 00:41:41.960 --> 00:41:49.920 align:middle line:84% P initial, V initial, P final, V final. 00:41:49.920 --> 00:41:52.305 align:middle line:90% And this curve is an isotherm. 00:41:52.305 --> 00:41:56.182 align:middle line:90% 00:41:56.182 --> 00:41:57.640 align:middle line:84% So we'll come back to these when we 00:41:57.640 --> 00:42:01.210 align:middle line:84% do heat engines and the Carnot cycle at lecture 4. 00:42:01.210 --> 00:42:08.460 align:middle line:90% 00:42:08.460 --> 00:42:09.250 align:middle line:90% We're almost done. 00:42:09.250 --> 00:42:11.040 align:middle line:90% Let's see, one last-- 00:42:11.040 --> 00:42:14.970 align:middle line:84% two last points here, intensive versus extensive properties. 00:42:14.970 --> 00:42:29.190 align:middle line:90% 00:42:29.190 --> 00:42:47.090 align:middle line:84% All right, intensive properties can be defined and measured 00:42:47.090 --> 00:42:53.815 align:middle line:90% at any point within a system. 00:42:53.815 --> 00:43:03.798 align:middle line:90% 00:43:03.798 --> 00:43:05.590 align:middle line:84% Would somebody like to volunteer an example 00:43:05.590 --> 00:43:06.745 align:middle line:90% of an intensive property? 00:43:06.745 --> 00:43:12.530 align:middle line:90% 00:43:12.530 --> 00:43:13.512 align:middle line:90% AUDIENCE: Temperature. 00:43:13.512 --> 00:43:14.720 align:middle line:90% RAFAEL JARAMILLO: Yeah, temp. 00:43:14.720 --> 00:43:19.588 align:middle line:90% 00:43:19.588 --> 00:43:21.130 align:middle line:84% When they take your body temperature, 00:43:21.130 --> 00:43:23.963 align:middle line:84% they assume that you have one body temperature. 00:43:23.963 --> 00:43:26.130 align:middle line:84% And they can take it-- there's different places they 00:43:26.130 --> 00:43:28.995 align:middle line:84% can stick the thermometer, but you should get the same number. 00:43:28.995 --> 00:43:31.880 align:middle line:90% 00:43:31.880 --> 00:43:38.090 align:middle line:84% Density-- now, you can locally define density, 00:43:38.090 --> 00:43:40.010 align:middle line:90% and you can measure it locally. 00:43:40.010 --> 00:43:42.710 align:middle line:84% Composition for a uniform system, composition. 00:43:42.710 --> 00:43:45.840 align:middle line:90% 00:43:45.840 --> 00:43:52.330 align:middle line:90% Pressure-- and there are more. 00:43:52.330 --> 00:44:15.300 align:middle line:84% Extensive properties depend on the extent of the system. 00:44:15.300 --> 00:44:18.480 align:middle line:90% And they scale with system size. 00:44:18.480 --> 00:44:26.740 align:middle line:90% 00:44:26.740 --> 00:44:41.660 align:middle line:84% So some examples here would be energy, volume, mass, entropy, 00:44:41.660 --> 00:44:43.460 align:middle line:90% and so forth. 00:44:43.460 --> 00:44:45.680 align:middle line:84% The doctor can take your temperature 00:44:45.680 --> 00:44:48.020 align:middle line:84% at several different places, but the way you-- 00:44:48.020 --> 00:44:49.640 align:middle line:84% your whole body has to be on a scale. 00:44:49.640 --> 00:44:52.790 align:middle line:84% They can't weigh you just by weighing your arm. 00:44:52.790 --> 00:44:55.250 align:middle line:84% So extensive, you need to know the extent. 00:44:55.250 --> 00:44:58.100 align:middle line:84% Intensive, it can be defined and measured 00:44:58.100 --> 00:45:02.257 align:middle line:84% at any point inside or within a system. 00:45:02.257 --> 00:45:03.340 align:middle line:90% Easy way to remember that. 00:45:03.340 --> 00:45:06.542 align:middle line:90% 00:45:06.542 --> 00:45:08.000 align:middle line:84% All right, we're going to end today 00:45:08.000 --> 00:45:11.675 align:middle line:84% with definition of the phases-- a phase of matter. 00:45:11.675 --> 00:45:23.368 align:middle line:90% 00:45:23.368 --> 00:45:25.410 align:middle line:84% So I'm going to define a phase the following way. 00:45:25.410 --> 00:45:28.020 align:middle line:90% 00:45:28.020 --> 00:45:49.290 align:middle line:84% Phase is a region within which all intensive properties are 00:45:49.290 --> 00:45:49.790 align:middle line:90% uniform. 00:45:49.790 --> 00:45:54.542 align:middle line:90% 00:45:54.542 --> 00:45:56.840 align:middle line:84% All intensive properties are uniform. 00:45:56.840 --> 00:45:59.800 align:middle line:90% That's a phase of matter. 00:45:59.800 --> 00:46:05.930 align:middle line:84% So, for example, solid sucrose, some things 00:46:05.930 --> 00:46:23.400 align:middle line:84% we've seen here-- water, simple syrup, grass, 00:46:23.400 --> 00:46:32.420 align:middle line:90% some examples on length scales. 00:46:32.420 --> 00:46:40.870 align:middle line:90% 00:46:40.870 --> 00:46:42.790 align:middle line:90% It's an important caveat. 00:46:42.790 --> 00:46:45.850 align:middle line:84% If I zoomed down to atomic length scales, 00:46:45.850 --> 00:46:48.633 align:middle line:90% I might say this isn't uniform. 00:46:48.633 --> 00:46:50.050 align:middle line:84% I've got different metal elements, 00:46:50.050 --> 00:46:52.065 align:middle line:90% depending on where I'm looking. 00:46:52.065 --> 00:46:53.440 align:middle line:84% So this has to be on length scale 00:46:53.440 --> 00:46:54.982 align:middle line:84% of large and molecular length scales. 00:46:54.982 --> 00:47:00.280 align:middle line:90% 00:47:00.280 --> 00:47:03.950 align:middle line:84% And phase boundaries, which, of course, 00:47:03.950 --> 00:47:08.610 align:middle line:84% are a really important topic in thermo and material science, 00:47:08.610 --> 00:47:19.380 align:middle line:84% are classified similarly to system boundaries. 00:47:19.380 --> 00:47:25.800 align:middle line:90% 00:47:25.800 --> 00:47:28.000 align:middle line:84% All right, so we have a two-phase system. 00:47:28.000 --> 00:47:29.905 align:middle line:90% For example, sugar and water-- 00:47:29.905 --> 00:47:34.470 align:middle line:90% 00:47:34.470 --> 00:47:43.737 align:middle line:84% we have some sugar, and it's in water. 00:47:43.737 --> 00:47:44.945 align:middle line:90% We have a sugar water system. 00:47:44.945 --> 00:47:49.290 align:middle line:90% 00:47:49.290 --> 00:47:55.780 align:middle line:84% And we're going to think about this boundary in the same way 00:47:55.780 --> 00:47:57.880 align:middle line:84% that we classified system boundaries. 00:47:57.880 --> 00:48:02.780 align:middle line:84% And so that's an open boundary because sugar molecules 00:48:02.780 --> 00:48:05.690 align:middle line:84% can go across the boundary into the water. 00:48:05.690 --> 00:48:09.330 align:middle line:84% And similarly, sugar molecules can come out of solution 00:48:09.330 --> 00:48:12.620 align:middle line:90% and go back into the solid. 00:48:12.620 --> 00:48:14.810 align:middle line:84% This is a boundary that exchanges volume. 00:48:14.810 --> 00:48:18.380 align:middle line:84% It exchanges heat energy, and it exchanges mass. 00:48:18.380 --> 00:48:22.500 align:middle line:90% 00:48:22.500 --> 00:48:25.320 align:middle line:84% Good, so that's all I had prepared for today. 00:48:25.320 --> 00:48:29.448 align:middle line:90% It is 10:54, almost perfect. 00:48:29.448 --> 00:48:30.240 align:middle line:90% Thanks for joining. 00:48:30.240 --> 00:48:33.120 align:middle line:84% As usual, hang out until at least 11:00 00:48:33.120 --> 00:48:35.930 align:middle line:84% if folks want to talk or ask any questions. 00:48:35.930 --> 00:48:38.190 align:middle line:90% Otherwise, I'll see you Monday. 00:48:38.190 --> 00:48:41.000 align:middle line:90%