 of this particular chapter, systems surroundings, and all these six statements. Very important if you understand the six statement, you'll understand the concept of system and surroundings. It looks like very simple, types of system, open, close, isolated, but this kind of statement is very important to understand. Okay. Next, next time we are going to see is right down the heading, state variables, state variables. It defines the state of a system, defines the state of a system. The various state variables are we have pressure, volume, temperature, mainly this tree. Okay. In gaseous state also we have discussed, if you want to define the position of a gas, you have to define the pressure, volume, and temperature at that point. Okay. When all the state variables right down, when all the state variables are constant, all must be all right, then the system is said to be said to be a particular state. The state variables for solid we define by, it's by the coordinate. Any object if you have, we use the coordinate system to define the state, x, y coordinate, like that. Okay. And coordinate also we have different coordinate system, Cartesian coordinate we have, polar coordinates we have. For fluids also we have similar kind of system. Done. Okay. Now you see if a given state, the pressure is a to b we have, suppose, a and b two states we have. At a the pressure is pa, va and ta. And b the pressure is pv, vb and tb. Okay. So when the system goes from a to b, so there will be a change in state. We're going to have this thing is possible that only one variable is changing, only two variable is changing, or all the variables are changing, anything is possible. All the three possibilities we have, only one, two, or all three variables are changing, possible. Right. So this change in state variable whenever it is happening, we say the change in state is also taking place for that. State, it means the position, not the physical change, like solid to liquid, liquid to gas, not like that. The position is changing, right, different states we have. So all these things which is happening here, like we must have certain path to change the state of a system, right. We must have a certain way to change the state of a system, right. So all these paths, the different way we have, we call it as processes, right. So change in position or a state of a given, you know, gaseous species is taking place by different, different ways. We have different, different path for this, and all these ways and paths are known as processes, correct. Like for example, you see, if the pressure is constant from A to B, then we call it as isobaric process. If the temperature is constant A to B, isothermal process, like that we have isochoric process when the volume is constant, when there is no exchange of heat adiabatic process. When the initial and final state is same, cyclic process. So like this, we define the processes. We will come back to this process thing again after some time, but before going into that, we will see thermodynamic properties, right down. Thermodynamic properties, we have two types, okay. The first one is extensive properties, right down. These are the properties which depends upon, these are the properties which depends upon, which depends upon the quantity or which depends upon the quantity or the amount of the substance present, which depends upon the quantities or the amount of the substance present. So what I said, it depends upon. Second one is intensive property. Important also, they ask this, properties in the exam also, very often, okay, important. Intensive property, you have to memorize all this. Intensive property is exactly opposite of it. It depends upon the quantity and amount of substance. It is independent of quantity or the amount. Okay, tell me. Density, density, intensive or extensive? Density is intensive, right? Don't get confused. It is an intensive property because suppose if you have water, so if you take one glass of water or one bucket of water, the density of water won't change, correct? So density is an intensive property. Don't get confused that D is equals to mass by volume. So since it depends upon mass, it is extensive, no. Yeah, that's what you see, what happens. I'll take one example here. You see, suppose you have a container, okay, and the mass here is 2M, 2M and the volume is 2V. I'm assuming this. What is the density in this case? M by V, 2 and 2 will get cancelled. So if the mass is 2M, density is M by V, 2 and 2V. Now suppose if you distribute this or distribute this into two equal halves, so that the mass of this side is M volume is V, mass of this side is M volume is V. What is the density of this part? The half part. Again, M by V. So you see, whether you take mass as M or 2M, the density is same only, M by V. Why it happens? Because when you change the mass in the same proportion, volume also changes and overall it makes the ratio M by V constant, correct? No, it's not like that. I'm talking about one particular type of object like suppose if you take water, density of water, you cannot mix something into it. Then it won't be the same thing because we have two different types of object present in this. You can take water, you can take benzene, you can take any other thing. Yes, for the same object, means if you're taking oil, then only oil, water, only water, chloroform, only chloroform, any gas, the same gas if you're talking about. The system is same only, amount is changing, we can say. Aditya, if you mix the same thing into the given system, then the amount mass of the system will change, but system will be the gas only or the liquid only, whatever it is. Suppose if you have one glass of water, correct? You can put some more water into it. The system is water only, correct? But the mass of water has been changed and in the same ratio, the volume will also change. So that M by V, the ratio is constant overall, hence density is constant. So this is for your understanding, what is intensive and extensive property, but there are many examples, especially for intensive property. We have so many examples that you have to memorize because in question, they'll ask you which one of this is intensive or extensive property. So one by one, we'll see the example. So write down, first of all, the example of extensive property. Heat capacity is extensive, mass extensive, volume extensive, number of moles extensive, Gibbs free energy, Gibbs free energy is represented by capital Z extensive, enthalpy, notation also you must remember, enthalpy is represented by H, again extensive, entropy, S extensive, and then we have internal energy. Internal energy is represented by capital U or capital E. Okay, both are same thing. So all these are extensive property, let's just say intensive, see one thing. Enthalpy is extensive property, okay? But when we write molar enthalpy, one just a second guys, okay. So yeah, so what I said, enthalpy is extensive when we write molar enthalpy. So molar enthalpy means what? Enthalpy of one mole. So when you write molar term here, it becomes intensive property because for one mole, it will be fixed, right? So enthalpy is extensive, molar enthalpy is intensive. Okay, similarly, when you write molar entropy, molar entropy, this also becomes intensive because it is again for one mole, correct? This is one thing that you must keep in mind. Apart from this, you see, all the concentration term are intensive property, concentration, for example, molarity, molality, okay? We can say mole fraction, all these are intensive property, concentration term, okay? We have already discussed density is intensive, temperature is intensive, pressure is also intensive, okay? Reflective index, you will study in physics, refractive index, also intensive, specific heat, specific term also if you have seen written here, specific means for one gram, molar means for one mole. So whenever you see these two terms, specific or molar written before any term, it is always intensive. Did you get it? Whenever a term starts with a molar or a specific, then it is an intensive property. This specific means for one gram, molar means for one mole, viscosity is always intensive, viscosity, surface tension, surface tension, dielectric constant, these terms you will get in physics, okay? You won't have any use in chemistry, but just example you must remember because they ask all these things in the example. Dielectric constant, we will discuss about pH in ionic equilibrium a lot, pH is also an intensive property, EMF of the cell, EMF also we will see in 12th class electrochemistry in the chapter, EMF of the cell is intensive property. Boiling point intensive, melting point intensive, either you take a cube of ice or you take a large slab of ice, its melting point is same, okay? So melting point is intensive, okay? Molar volume, you see here, volume is extensive, I have written here, volume is extensive, but when you write molar volume, it is intensive, specific volume also, specific volume also intensive, okay? Resistivity, conductivity, conductivity, resistivity, all these are intensive, yes copied? Pressure is intensive only, no, you see like it is, you will study, you will understand this thing in a better way, once you understand the concept of vapor pressure, okay? Vapor pressure is independent of the amount of vapor that is present, right? It depends upon the temperature only, at a given temperature, the vapor pressure of water is fixed constant, okay? That value won't change no matter what amount of vapor you are taking, okay? There is an equation called Clausius-Clippron equation, okay? That equation relates vapor pressure and temperature, and there is nothing like amount of vapor we are considering in order to derive that expression, okay? So we'll discuss that later, okay? In chemical equilibrium we have a bit of it, and then in discuss, in detail we'll see this in solution chapter in grade 12, okay? So for now let's just keep this in mind that pressure is independent of amount, it is an intensive property, okay? So all these properties are important guys, so you must take care of this, okay? They ask this question in the exam that which is intensive or extensive property, okay? So this is the thing we have, so these two things are important, one more thing you see here, I'll tell you, density what I said, one relation you try to understand, density, density is mass by volume, correct? Density is mass by volume, correct? So density we have discussed this, it is an intensive property, I'm just trying to make you understand one relation here, it is intensive, what is mass? Mass is extensive, volume is also extensive. So what we can conclude from this relation that whenever we have the ratio of two extensive property, the ratio becomes an intensive property, right now on this note it's very important, ratio of two extensive properties becomes intensive, okay? Sorry there was someone, so I have to attend them, okay? So understood, right? See volume is extensive, if you take, you know, more mass if you take, it will occupy more space unwrapped, right? So no, whenever you change the mass, obviously it will occupy more space, so mass and volume are related, hence it is extensive, got it? That's not an issue Aditya, whether it is linearly or not, right? That's not an issue but whenever we have the ratio of extensive, it is always an intensive property. Yes, if you have the kind of thing that you are asking in the same proportion if mass and volume is not changing, right? Then we'll have some difference but usually it doesn't happen, right? So we consider that linear relation of mass and volume, yeah that's what Anuradha was talking about, right? So you just consider here the linear relation, right? So this is one very important, you know, aspect we have of this, with this you can easily understand and memorize those, you know, examples that we have done because it's very important. This is the first thing that they ask very frequently in this chapter. Now after this we need to understand thermodynamic functions, okay? Write down the heading next, thermodynamic functions, okay? Thermodynamic functions. Two types of thermodynamic functions we have, first one is state function, state function. So state function is the one which is independent of path, independent of path. Like, I'll give you some examples also, first let me write down all these things. State function is independent of path, it just depends upon the state of the system, like initial and final state, that is it. Path function is the another one, path function which depends upon path, okay? It is independent of path and this one depends upon path, depends on path, once again Anuradha, once again. You see, if you have this point A and from this point A you want to go to point B and we have certain, no, what we say, variables here, right? P-A-V-A-T-A, P-V-V-T-B. So function is the collection of those kind of variables. So function is what, it is a collection of those variables which is independent of path. Now what I say, you have to go from A to B, how would you go? There are infinite number of paths, right? You can, one thing is what, you can go directly from A to B. This is one way possible. Another is what, you can travel like this, you know, whatever the way you like. You can travel like this, okay? You can travel also like this. So like this, we have infinite number of paths possible, isn't it? But the final state is B only. It's like you want to go to, you know, Chennai from Bangalore, right? So you can go directly to Chennai or you can go to Hyderabad and then Chennai, go to Delhi and then Chennai, whatever, right? So there are infinite number of paths possible. But the destination, final destination is what, is Chennai only. So here it is B. So A and B, two points we have, there are infinite number of paths possible. Now suppose there are three paths I have drawn over here. Tell me, if you, if you talk about the, you know, in terms of work, work done, right? Which path will give you, will require maximum work done, one, two and three. Which path will require maximum work done? Or simply if I ask you, in which path you have to put more fuel? Third, because this path is the longest one. Longest one, the longest, the maximum amount of fuel is required for this, okay? Means if you talk about heat, if you talk about work, if you talk about any kind of energy, all those energies are path dependent, okay? Dependence upon path. Like if you go from this path, you will have a certain amount of energy required, fuel required. This certain amount of fuel required, this maximum amount of fuel required. So work done or heat or any energy if you think of, all these things are path function. Is it, is it clear? So we can write the example here, heat, work done, all our path functions, isn't it? It depends upon the path that you choose, correct? Independent is what? Independent of path state function, we can think of pressure, we can think of volume, we can think of temperature, we can think of enthalpy, we can think of internal energy, Gibbs free energy and entropy. All these are state function. Means if the pressure at A is PA, pressure at A is PA, B is PB, no matter what path you choose, one, two or three, the pressure at B is always PB, correct? Volume VB, temperature TB. Are you getting it? That's why the pressure and all other terms, variables that I have written, all other variables are state function. It just depends upon initial and final, does depends upon the state of the function, the state of the system. Yes, clear? Any doubt in this? Tell me, heat means energy we are talking about. Heat in the sense of energy we are taking. Heat, as in you can say heat exchange, okay. So longer path you need to travel, so more heat will be, you will get exchange. Clear? Any doubt, guys? Speak up. Any doubt till now? Because these are the basic understanding, we'll have the application of all these things later on. Okay, so you have to understand this. Enthalpy will discuss terms, Aditya will discuss enthalpy and all, we'll discuss that a bit later. Just you keep the example in mind, we'll see definition and uses of this, everything we'll discuss later. Okay, like I said, this is just an introduction going on. Okay, like I said, there are so many things we need to understand new new terms we have, so we're trying to understand that. Enthalpy, if you want, I can tell you just one line over here. It is a heat content of the system at constant pressure. Right? At constant pressure, what is the heat content is the enthalpy of the system. We'll see that later, we'll discuss. Okay? Clear? Enthalpy is represented by H, U, I already said it is an internal energy, gives free energy and entropy. This notation you must remember. Okay, next. Write down thermodynamic equilibrium. Write down, a system is said to be, a system is said to be in thermodynamic equilibrium, thermodynamic equilibrium when, when it is at thermal, chemical, and, and mechanical equilibrium. All three types of equilibrium are there. Then it is at thermodynamic equilibrium. Okay? So what is thermal equilibrium? Thermal equilibrium is based on temperature, same temperature, right? So I'll just write down quickly this thing here. Thermal equilibrium, it is based on, based on temperature, constant temperature we have. Okay? T constant. There's no heat flow because the temperature difference is not there, thermal equilibrium, right? One at 100 degrees Celsius, other one at 50 degrees Celsius. If you keep them close to objects in contact, then there will be heat flow from 100 to 50. The heat will flow until the temperature becomes equal for both the objects. Okay? So when it is become equal, we say that two objects are in thermal equilibrium. Okay? Chemical equilibrium, excuse me. You see, chemical equilibrium is related with concentration, right? So constant concentration if you have, constant concentration. Then it is in chemical equilibrium. We'll discuss this in detail in the next chapter that is chemical equilibrium. Chemical equilibrium is this, constant concentration. Okay? Mechanical equilibrium, mechanical equilibrium, net force is zero, right? Net force is zero, or we can also say equal pressure. Force is nothing but pressure, pressure is force per unit area, correct? So when pressure is equal, force per unit area is also equal. So equal pressure we have. Okay? One note you write down. This is the assumption that we take wherever we apply the concept of thermodynamics, write down. Thermodynamics deals with, thermodynamic deals with the system which are in, the system which are in thermodynamic equilibrium. Thermodynamic deals with the system which are in, system which are in thermodynamic equilibrium, correct? You won't get any question on this, just for information you should know. Okay? That whenever we apply the concept of thermodynamics, we assume the system is in thermodynamic equilibrium. Okay? So this is for thermodynamic equilibrium. Okay? Next we are going to see thermodynamic processes. What is the process? Write down. It is an operation. It is an operation by which a system, system is changing its state, is changing its state. It denotes the path followed, path followed by the system, by the system while changing the state. Okay? So what is the path by which the system is changing the state? This path is the process. That is what I have discussed a few minutes back. A to B, the system is going on, pressure is getting changed. So whatever path we have possible from A to B, all those paths are called one kind of processes. Okay? When I say system is changing its state, yes, all paths we can say. All paths we can say. Right? So when I say, when we say the system is changing its state, so change means what? You see the changing in state. Now this change also can be of three types, physical change, chemical change or change in state variables. Okay? Change, you see, it is also of three types. We have physical change. What do you mean by physical change? Physical change means chemical change. And then the last one we have, we have change in state variables. So physical change means state is changing, right? Solid to liquid, liquid to gas, all these that you have is physical change. Chemical change is the reaction like reactant to product, the conversion. And change in state variables, change in state variables is the change in pressure, volume, temperature, all these state variable change we have. Copy this down. Now what are the different, different processes we have? We'll discuss all these processes. The most important one we have, S is solid, L is liquid state. Solid, liquid and gas. State change. Done? Done? Okay. Few processes that we already know we have discussed it. The first one you see, we have isothermal process. What is isothermal process? Iso means equal, thermal means heat. Right? So isothermal process, we have constant temperature process, constant temperature process. Isobaric. What is isobaric? What is isobaric? Iso is again same, bar is this, bar is the unit of pressure. So it is constant pressure process. And the third one in this chain we have, isochoric. Okay? Isochoric. It is the third variable that is constant volume. So this you must remember temperature, pressure and third one is volume. Okay? Apart from this three, the next one we have adiabatic process. Adiabatic process is the one right down in this process there is no exchange of heat. There is no heat exchange. Delta Q. Q stands for heat, delta Q is zero. After this we have cyclic process. Cyclic process is the one in which the initial and final state is same. Right now, initial and final state is same. For example, you see consider this process. Okay? You start from A and then you go to B, then from B you go to C, C you go to D and then again from D you go to A. So initial state is A, final is also A, cyclic process. We can have a circle also like this. Okay? This we can also consider as the cyclic process. This is a cyclic process. So initial and final state is same, it is a cyclic process. Now when initial and final state is same, all the state variables are what? The change in right down here, since initial and final state is same, the change in all state variable, in state variable equals to zero. Like if you write down delta P, delta P pressure is the state variable. Delta P means what? PF minus PI, final minus initial. F stands for final, I stands for initial. Since initial, final pressure is same only because the state is same. So this is equals to what? Zero. Any doubt in this? Delta V equals to delta T equals to delta U equals to delta H equals to delta G equals to delta S equals to zero. All these change in state variables is equals to zero. P is the pressure, yes. If it is anything else, I would have told you. P is pressure, yeah. Copy all of you? Yes, yes, yes. This entire thing till here is cyclic. Done? Okay. You have done this chapter in physics and you must know if PV relation is given, PV graph is given, how do you find out work done? PV graph is given, how do you find out work done? Area under curve, right? Yes. Area under curve, we do that in PV graph. Okay. Yes. Sometimes what happens, they don't give you PV graph. They give you PT graph or VT graph. So if you are able to convert this PT or VT graph into PV graph, you can find out the work done easily. Okay. So how do you do that? We'll discuss that first. So heading you right on, we are discussing all these things under process only, right? So process will have very much, very, you know, a lot of things we need to discuss in process. So we are discussing this under process. So graph conversion you write down. Based on the process, how do we draw the graph which is not given here? So you see what happens? Now you see we have PT graph, suppose we have given, and the PT graph is this, starts from origin. Okay. This is point A. This is B. This is C. Process is this only, right? Process is this only. I have just drawn this line here to origin so that you understand that this line is passes through origin, just for this information. Okay. This is the PT graph given. You need to convert this graph into PV first graph into PV. And then we'll see how do we convert this into VT. This is the graph we need to do. So you see in this, along this AB process that we have, what is this process AB? What is constant from A to B? If you go A to B, compare this from PV is equals to NRT. How it is P constant from A to B? Yes, temperature is everywhere in Kelvin, mother. Yes, V is constant. Consider this guys, consider this one. PV is equals to NRT. If P and T will have a straight line passing through origin, it means V is constant. AB, the process is isochoric. No doubt. Similarly, BC, could you tell me? BC, we have constant temperature line, right? It is isothermal. And what is CA? CA is isobaric because the pressure is constant. So all these three process we have. Correct. Now we need to convert this into PV graph. How do we do that? We know PV graph at constant temperature. What it would be? Listen to me carefully. PV graph at constant temperature, it will go like this. Yes or no? Yes or no? Right? Now, we have to understand that it is a constant pressure temperature graph we have and constant temperature graph here it is B to C. It is a constant temperature graph. It means this point is either B or C. If it is B, then this point should be, this point should be, if it is B, then this is C. If it is C, then this is B. These are two possibilities. Yes. So we have to just cross check this, which should be B, which should be C. That is the first thing. So what I am telling you, I am just taking this top is the B and bottom is the C, for an example. And then we will cross check in the last that our assumption is correct or not. So what I am telling here, I am telling this is B and I am taking this as C. So this is the graph we have B to C. I am just taking this as B and C. If it does not hold true for the entire process or the other process, we have to change it on. But you need to, like this only you need to guess and check. Okay. Now, since I have taken this, because PV graph at constant temperature is this only now. Hyperbola constant temperature PV goes to NRT, T is constant. So PV graph is what? It's like this only a different temperature. Yes. Anybody has doubt in this graph at constant temperature? Anwar, tell me, did you understand this? Have you done this in a, guess is it also not? When temperature is constant, boy's law, the graph is this, like this it goes. Remember? Yeah, the same graph we have here. Correct? So what I have assumed here, B is this, C is this. What is happening from B to C? You see the pressure is decreasing and the volume is increasing. What happens over here? The pressure is decreasing. Obviously, when the pressure decreases, right, temperature is constant, volume will increase. It means the assumption that we have taken that this is B, this is C is correct here. If you consider this one, if you consider this as C and this as B, then B to C is this. B to C, the volume is decreasing and pressure is increasing. Relation is not wrong, but it does not suit this particular relation that we have here. From B to C in this graph, what we have, pressure should decrease because it is decreasing here. So pressure is decreasing, temperature is constant, so volume is increasing. So here also we have the same thing. From B to C, the pressure should decrease, then the volume will increase and the temperature is constant. It does not suit this particular graph here. That's why I'll do this change here. What I'll do, I'll again go back to the initial assumption that we had. This point is B, this point is C and the process is this. All of you understood this? Yes, clear. Tell me first, right? Now, we have two options for A, like two places for A, not option, places for A. Either we can take A this side or we can take A this side. Yes, is there any other possibility? We can take like this only, then only we have A, B, C line like this. Cannot place this here. Symmetrical arrangement basically we are considering, correct? So suppose if the, this one you are taking, so I'll go like this, A to B and then C like this. So A to B, B to C, C to A. So A to B, what is happening you see? What is happening A to B? A to B, you see the volume is decreasing, pressure is constant. A to B, you see. Do we have constant pressure A to B? Do we have constant pressure A to B? Yes, tell me. Do we have A to B, constant pressure? No. A to B, you see the pressure is increasing. It means this assumption is what? This assumption is wrong. We won't take this. Just remove it off, correct? Now, this is A. So line should go like this. This will come down and then like this it goes, okay? So A to B, so the process direction is this. A to B, then B to C and then C to A. So what is happening in this, you see? A to B, we have constant volume, pressure is increasing. Again, here you see. A to B, we have constant volume, pressure is increasing. B to C, we have constant temperature, pressure is decreasing, volume is increasing. B to C, constant temperature, pressure is decreasing, volume is increasing. C to A, we have constant pressure, volume is decreasing. C to A, we have constant temperature, temperature is decreasing, which means volume is also decreasing, temperature and volume. Hence, this graph is the correct conversion we have this side. Once again, I'll explain, wait. How many of you understood this conversion? Understood? Okay, so I'll explain. One more thing, one more way, you can understand this. One more time we'll discuss this. See, if you don't want to take A over here, then you can take A this side, suppose. But if you A take here, then this is A to C process, this is A to B process. So what happens from A to B, you see? The pressure is constant, A to B, you see, the entire line, the pressure is constant. But here what happens? Here A to B, the pressure is not constant, it is increasing. Yes, Anurag, you understood what I said? A to B, if you consider this A over here, right? Pressure is constant, but here the pressure is not constant. Hence, this assumption of A being here is not correct, right? And we know A to B, we have constant, you know, we have constant volume process, B to C, constant temperature, C to A, constant pressure process, right? That's why we are trying to have this A either on this side or this side, because that is the only possibility we have. When you practice some questions, you will understand that how do we think about these points, okay? So obviously, this point is not correct. So we'll just eliminate this out. And we'll take a point over here. Then you connect A and B, A and C, and you cross check the entire relation that we have given in this graph. Does it hold true here also or not? If it is true, it means the graph is correct. If not, it means you have done some mistake into this. Tell me, is it clear? Clear? No doubt? Okay. Try this conversion, B to T. B to T, first of all, is a constant temperature process where we have. Constant temperature is B to C. B to C, we have constant temperature. So we can have a line, we can have a line like this, which gives you constant temperature line. Suppose we have a line like this, constant temperature line, B to C. Yeah. Should we place, now we know this line is B to C process. But where is B on the top or on the bottom? Where is B on the top or on the bottom? Okay. So we'll take it on the top first. If you take this on the top, then B to C, what happens? B to C, the volume is decreasing. B to C, you see here, what happens? The pressure is decreasing. When pressure decreases, volume increases. So this assumption is not correct. Did you understand? Tell me. Yes, yes, you can do that stress, no problem. Yes. So B to C, we have checked what volume is decreasing. So here also volume should decrease. But what is happening? B to C, pressure is decreasing. Pressure and volume are inversely proportional. It means the volume is increasing. It means our assumption is wrong. And the correct assumption is this. B we must have here. And C we must have here. This is a process B to C we have. No, no, I'm just, you never know C, Anurag. This is what you need. But they can give you BT, PT, anything they can give you. So you should know all these converters. It's not like I'm going from this to this and this to this. I'm just trying to convert this into this, this into this so that you can do all kind of convergence. Okay, just for practice. Yeah. B to C is this. Now, C to A is constant process. It means C to A process must pass us through this origin. Then only the pressure would be constant, isn't it? So I'm assuming A somewhere here, C to A. So this is A and this would be B to A, straight line. So this is A we have here. So B to C, C to A and A to B. Now you can cross take all the data, you'll get it right. C to A you see what is happening. Volume is decreasing and temperature is decreasing. C to A you see. C to A pressure is constant, but temperature is decreasing. C to A temperature is decreasing. A to B constant volume, temperature is increasing. A to B constant volume, temperature is increasing. So this is the graph we have of BT. Isn't it clear? Tell me any doubt. No. Okay. Fine guys. So we'll take a break now. After the break, we'll see two more processes here, reversible and irreversible process. Okay, take a break. Seven o'clock, we'll start.