 next write down thermodynamic equilibrium. Sir, yes. And graph is alleromical. No, no, what I was trying to explain here that if you are at point A and if you are coming to this point B, you can have many path possible like this. But when you are at this point B, your pressure will be P2B2 and T2 only irrespective of the path followed. So that is why a pressure volume temperature is a state function. It depends upon initial and final state, not the path followed in this state. But work if you see, suppose work example, if you take this path is small, right? So here if you come here to here by this path, work then will be less. But if you follow this path, work then will be more, right? So work then is what? Work then is path function. It depends upon the path we choose, right? So that's why the path function is what? Anything that is related to work, work or energy, that's what we have, right? Next slide on thermodynamic, thermodynamic equilibrium. What is thermodynamic equilibrium right now? When a system is at, when a system is at thermal, chemical and mechanical equilibrium, then it is said to be in thermodynamic equilibrium. All three equilibrium are there, then it is thermodynamic equilibrium, right? When the system is at thermal, chemical and mechanical equilibrium, it is said to be in thermodynamic equilibrium. Mechanical means when the pressure is same, two side if you are applying the same pressure, it's not moving. Suppose you have an object, you have the same pressure, okay? So it won't move, that is mechanical equilibrium. Chemical equilibrium is what? When concentration is same both side. So if you have a top spinning and it's a, if I have like a top that's spinning, but it's a chemical and thermodynamic equilibrium, then. No, that is see, when you have a top spinning, right? So there's no transliterary motion into this. There's a circular motion on its own axis, right? But the point is you have an object. I'm trying to explain what is mechanical equilibrium. You have an object like this, okay? If you apply some force from this direction, which is nothing but, okay, you're applying some force from this side and the same force from this side, right? And these two will cancel out each other, right? So this is in mechanical equilibrium. So is there any object that's moving is not in thermal equilibrium? Not in thermal equilibrium, yes. No, no, no, not in thermal equilibrium. Thermal equilibrium is when temperature is same both sides. Sir, velocity is constant. What? When the equal force is there, there's no movement into this. There's no net force. Sir, velocity is constant. Velocity is constant means what? There's no acceleration. And the constant acceleration motion we have now. Constant acceleration motion is possible, no? An object can move with a constant acceleration, but it's possible. So that is not thermal, and that's not mechanical equilibrium. When net force, simply one thing you'll keep in mind, when net force is zero, there's no net movement. Then it is mechanically. Constant velocity means access is zero, right? So when there's no acceleration, then you can say, yeah, it's fine. That's fine. Point is, mechanical equilibrium when net force is zero, F net is zero. Chemical equilibrium, when I say, it means, chemical equilibrium is when concentration, concentration is zero. There's no net concentration. And when we say, what is the next one? Mechanical, chemical is thermodynamic equilibrium. Thermal equilibrium is what? When temperature is constant, delta T is equals to zero. Temperature is not right. So when all these three types of equilibrium we have, then it is said to be thermodynamic equilibrium, right? One more thing you can say, thermodynamic equilibrium is defined, right down. Thermodynamic equilibrium is defined. What is T? What is C? Concentration. Concentration. Chemical equilibrium means what? Concentration. Concentration. So that's why, because concentration is zero both side, right? Concentration must be same both side, okay? Thermodynamic, right down, it is, what did you write? What is the first time? Thermodynamic. It is also defined as, as the state where all the state variable is fixed. There's no change in the state variable, right? In thermodynamics, we always deal with, we always deal with the system which is in thermodynamic equilibrium. Always deals with the system which is in thermodynamic equilibrium, okay? Next write down, thermodynamic process. We are just looking at the different terms now. Thermodynamic process. Write down into this. Write down, it is the path by which thermodynamic process. It is a path by which a system is, path by which a system is changing its state, okay? The various different process you write down. Isothermal, isothermal, in bracket this is short to write down, in bracket. Constant temperature. Constant temperature. Isobaric. Constant pressure. Isocodic. Constant volume. Isocodic, C-H-O-R-I-C. Isocodic. There is no exchange of heat. Delta Q is 0. For adiabatic, delta Q is equals to 0. No exchange of heat in this, okay? And we also call it as isocentric. Sorry, isoentropic. Isoentropic process. Entropy will also be constant in this. When delta Q is 0, entropy will also change. That we will discuss later. Entropy we will see after second law of thermodynamics, okay? Isoentropic we also call it as. Next write down adiabatic, okay? And then cyclic process. What is cyclic process? What is cyclic process? It starts and ends at the same state. Initial and final state will be same, okay? Initial and final state will be same. This is an isociclic process. We start from A, goes here, B, and then C, and then D, and then Q. Okay? So cyclic process, initial and final state is same. Is it also reversible? That depends. That depends. It's not necessary. That depends. So same as isoentropic. Say one of them must have an radioactive decay. It will give out another particle and change the rate of entropy. No, I'm talking about delta Q is equals to 0. Heat exchange will be 0. Then it is isoentropic. No, not delta T. So I said if one of the particles inside your system, another radioactive decay, it will give out another particle and change the entropy. What entropy will change? Entropy of system will change. So if the system entropy decreases, surroundings entropy will increase by the same value. Sir, the system entropy will increase. Whatever. If one changes system entropy if it is decreasing by the same amount, the surroundings entropy will increase. And radioactive decay we are not considering. That is a very rare case. So radioactivity we are not considering. So anyways we can write the system if you have isoentropic when delta Q is equals to 0. Radioactivity decay we are not considering. But again if you consider radioactivity decay, system entropy decreases by the same amount surrounding entropy increases. The delta S of the total system of the universe will be what? 0 in that case. One decreases, other increases. So delta S will be 0. So entropy we will discuss later. One very important thing here. In the process we have initial and final state is same. So if you find out the change in all the state function. What is the state function? Any example? Delta U. In internal energy state function, what do you have? Delta U. So what is delta U in a cyclic process? Delta U. Delta U is what? Change in C. If you have first A and B, if it goes to A and B like this, here the internal energy is UA and here it is UB. So what is delta U? Delta U will be UB minus UA or magnitude if you are considering. It is the difference we have. So since we have cyclic process, so all the state function, since it does not depend upon the path followed to gain that state. So that change in all the state function will be zero. So delta U will be zero. Delta G will be zero. Delta P will be zero. Delta T will be zero. Delta H will be zero. Delta S will be zero. All these things will be zero. Delta T will be zero. Delta B will also be zero. So change in state function in cyclic process will always be zero. Very important point. Okay? Since sometimes the conversion of graph is important and you need to do this while solving problem. Suppose you see this graph, we have pressure and volume. A, B and C. This is the graph we have. It is given. Now you need to convert this into PV graph. PV given. You need to convert this into Pt. And you need to convert this into Vt. Vt. Just a second. PV. PV. It is Pt. It is Pt and it is PV. So this graph is given. You need to convert this into PV graph. This graph, you need to convert into PV graph. Suppose it is given. How do we convert this into PV graph? And this into PV graph. Okay? It is similar. Work if you take the time pressure. We are already the same. See, first of all it is important QM. You know PV graph, you know, work done when calculating PV graph, you know area under the curve. You know work done in PV graph is work. Area under the curve. So sometimes if PV graph is given, you can find out the area that will be the work done. Magnitude you can get easily. But sometimes they will give you Pt graph and work done suppose you need to find out. So this area we cannot find out to get the work done. But work done part we will see later. But you see from this graph, can you tell me what is this process? A to B. What process is this? A to B. What is A to C? A to C. What is A to C? Constant pressure. Isoparic, right? It is isoparic. What is B to C? Isoparic. Isoparic. Can you tell you what is A to B? Isoparic. Isoparic because you see this graph is touching this origin. So it is a straight line like this. Which is the constant volume only? Pt graph has constant volume. Passes through origin. A to B is what? Isoparic. Now can you do this? Isoparic means volume constant? Right. Suppose A to B is this. Volume constant. So A to B. And then isoparic is A to C. A to C is this suppose. B to C is isothermal. So isothermal is what? Constant pressure. So temperature which is this? So this is A. This is C. And this is B. A to B. B to C. And C to B. And I guess it is... That is what I told you. See this is... Suppose B to C is isothermal. So how is isothermal graph? Pv graph. Constant temperature is this graph. This one? A to B to C. A to B is constant volume. Isoparic. C to A is constant pressure. Isoparic. Which way? This way. Okay. Because of magnetic field. A to B. Pressure is increasing. A to B. Pressure is increasing. If you do like this. That is B to A. Pressure is increasing. Can you do this VT graph? Try this VT graph once. VT graph you tell me. So isoporic is A to B. So this is suppose A to B graph here. B to C is isothermal. So B to C is isothermal. And C to A is isobaric. Isobaric is constant. Pressure, right? Sorry. Constant pressure will be this. Right? Yes. And will have this. B to C. Pressure decreases, right? Pressure decreases. B to C pressure decreases. And B to C is isothermal process. So B to C. Pressure decreases. Let me write this first. A to B is what? Isoporic. A to B is isoporic. So B will have this. I'll make some mistake. B C is isothermal. So this is B and this is C. And A B is isoporic. So A to B is this. Isoporic. C to C is isothermal. And C to A is. Isoporic. Sometimes they ask you this conversion in question also. If you want graph corresponding to this, what is VT graph? Because if it is VT graph you are drawing. So at constant pressure the line must pass through horizon. Why is it goes to MX? VT PV is equals to what? Minarity. VT graph if it draws a constant pressure we have supposed to pass through. Okay.