 Yeah, now the next is write down state variables. What are the state variables all these terms? We will understand today. Okay, there are so many terms. We need to understand processes we need to understand because we'll be using these terms very frequently in this chapter. We haven't done this kind of thing chapters before because we were doing atoms new gas pressure volume, right? P is equals to NIT density electrons proton that is what we were discussing, right? But this is different. Okay, we are having a different different terms that we will be using. So first of all, you should be familiar or comfortable with all these terms, then only you will be able to understand the concept. Okay, a state variable is not that the state variable is something else. You're talking about a state function, that is what I'm talking about. Okay, terms you understand properly. The one that you are talking about depend upon a state not on path that is a state function. Isn't it? I'm talking about state variables, state variables means what? Suppose the position of an object. How do we define the position of an object? What I'll do, I'll take the help of Cartesian system, Cartesian coordinate. So I can say this point A is 3 unit on x-axis and 2 unit on y-axis, 3, 2. So the coordinate of this point is what? 3 comma 2? Yes or no? So this is the variable we are using to explain the position of point A there. Yeah, that's right, that's right. Okay, so what are variables we are using to explain the or to define the position of an object, which is mostly gaseous over here. Correct. So in gaseous state also we have discussed it that the variables are pressure, volume and temperature mainly. Okay, a fixed position will have a fixed pressure, fixed volume, fixed temperature. Correct. That will change only when the position will change. At this point you see we have a fixed value of pressure here, a fixed value of pressure, volume and temperature. If you change the position somewhere here, then here we'll have some different value of pressure, volume and temperature. So variables are what? Variables are the terms which defines the position of an object. So mainly for objects like heavier object, now that we use Cartesian system, here for gaseous we use pressure, volume and temperature. Understood. So this we call it as state variables. Sorry, write down the definition quickly, all of you. Definition write down. Variables which defines the state of a system is called state variable. Variable which defines the state of a system is called state variable. Example, we have mainly three state variables we have. That is pressure, volume and temperature. Three state variables we have. Okay, next I'll write down when all the variables, when all the variables, state variables, when all the variables are fixed, not changing, it is fixed. Then we say that system is at particular state. When all the variables are fixed, then we say the system is at a particular state. So you have a state over here. This state will have certain pressure, certain volume, certain temperature and this will have certain volume, certain pressure, certain temperature. So suppose this is state A, this is state B. So here we define pressure suppose P A, V A and T A. Okay. And then here it is P B, V B and T B. Now how do we get this, how do we have this change in a state? Okay. So we can have various possibilities. So we can go from A to B by infinite number of parts basically. We say there are infinite number of parts but practically it is not there. We have to study four, five parts over here. So point I'm trying to make that you can go from point A to point B. There are many different ways, right? You can go like this. You can go like this. There are many different ways we can have from A to B if you want to go. All these different parts that we have, we call it as process, understood? Process. You must have done isothermal process, isometric process, isochoric process, reversible process, irreversible process, many things, correct? So the path by which change in state variable is there, right? One or more than one, that is not the problem, right? If only one state variable is changing, then also we say a system is under process, okay? If more than one state variable is changing, then also we say the system is under process, okay? So all these paths by which change in state variables is there is possible. We call it as processes, right? What are different, different processes? We have few examples I have given you, right? That is isothermal, isochoric, isochoric, adiabatic, many other things, right? So all these state variables we will see, sorry, process we will see later on, but that is how the change in state possible by different, different paths which we call it as, you know, which we call it as processes, correct? So state variable is this, next. Right on next, thermodynamic properties, thermodynamic properties. See, mainly we have two types of properties. The first one is extensive properties and the second one is intensive property, okay? First you write down extensive property. These are the properties, these are the properties which depends upon, which depends upon mass or the amount that you are taking, right? Amount or mass that you are taking, okay? Extensive properties are additive in nature. We can add two extensive property. Example I will tell you, with example you will understand additive in nature, additive in nature. So example if you see of extensive property, examples we have mass. Mass is an extensive property, isn't it? Okay, you have an object of 2 kg mass. For example, suppose this is the object of 2 kg mass we have. And if you place a block on this of 1 kg, what do you say? What is the total mass here in this direction? What is the weight component here? You will say mg and m is what? m is 2 plus 1 3? Yes or no? This kind of question you must have done in physics. So this is why we are adding the 2 mass here, right? 1 plus 2 because mass is in extensive property. We can directly add the 2, okay? So other examples, examples you must remember in need exam, in others exams also, they have asked this question many times that which of this is an example of extensive property, okay? The first definition the mass I have given, the example I have given that is mass. Then we have moles, then we have volume, then we have energy, energy, U, internal energy. What is H stands for? Tell me what is H stands for enthalpy? What is G stands for? Gifts free energy. What is S stands for? Entropy. S stands for entropy, correct? So all these terms are extensive property, right? Apart from this resistance is an extensive property, okay? Heat capacity is also an extensive property. Examples you must remember. I will tell you a few tricks by which you can memorize, you can understand the examples, but yes, you have to memorize this, important this one. Whatever we have done so far, this portion is the most important one. What is density? Density is intensive, right? That's why density is non-additive. You mix oil and water. Yes, you mix oil and water, so you cannot say the density of the mixture would be density of oil plus density of water that you cannot say, correct? And one more thing you can understand. If you take water, so if you take one spoon of water or one bucket of water, the density of water won't change, right? Right? That's why density is an intensive property. That intensive property is what is the one which is independent of the amount or the mass of the substance. So the second property, thermodynamic property you write down, that is intensive property. Intensive property, we have many examples, write down, these are the properties which is independent of, which is independent of mass, independent of mass and non-additive in nature. It is non-additive, non-additive. Okay. Examples of intensive property, we have pressure, intensive, then we have temperature, pressure, temperature, density, intensive, all concentration term. Any concentration term you pick, all concentration term are intensive. Molarity, molality, concentration term are intensive. Okay? Mole fraction also a concentration term, intensive, correct? Boiling point, boiling point intensive, melting point intensive, boiling point, melting point intensive. No, molarity won't depend upon mass, it won't change. You take two liter of coca bottle, correct? And you put this into a glass, right? So the glass one and the bottle one, the test will be same, it won't change because molarity is same, concentration is same, right? Boiling point, melting point, we have conductivity, we have conductivity, resistivity, conductivity, resistivity, molar volume. See one very important point I'm telling you here, volume is what? Intensive or extensive? Volume is intensive or extensive? Yes, so volume is extensive, but molar volume is intensive because molar volume is volume of one mole, right? Molar volume is the volume of one mole, hence it is intensive. So whenever you see this term, molar term are specific. Okay, molar term are specific. These two terms, if it is mentioned there, it means the entire term is intensive in nature. Molar means for one mole, specific means for one gram, are you getting it? Yes, tell me, whenever you see molar volume, molar enthalpy, enthalpy is what? Enthalpy is extensive. So if I write down molar enthalpy, it becomes intensive. So molar term is mentioned, it is for one mole, it is enthalpy. It is intensive. Molar enthalpy is intensive, okay? Molar entropy is intensive because molar term is written over there. Molar entropy is intensive, okay? Heat capacity is extensive, correct? Heat capacity is extensive, but molar heat capacity is intensive. Yes, yes, molarity is also intensive, yeah. Molar heat capacity is intensive, right? Specific heat capacity, again specific heat capacity, intensive. So whenever you see molar or specific word written, it means it is an intensive property. Without any thought, you can go with this, okay? Refractive index, reflective index, intensive, okay? Viscosity, viscosity, intensive, surface tension, intensive, dielectric constant, dielectric constant, intensive, pH value, intensive, EMF of the cell, of cell, intensive, copy this down. What is solubility? Intensive or extensive? Solubility is intensive, okay? Because the definition of solubility, if you see, it is the ability of a compound to get dissolved in any solvent at a given temperature. So it is temperature dependent process. Usually, you don't define this in intensive or extensive, but if you ask, we'll take a particular temperature and at that temperature, no matter what amount of solute you have put in, a fixed amount will get dissolved, okay? So it is an intensive property. One more very important relation you try to understand in this. Density, we all know. Intensive or extensive, we have seen density is intensive. Density is equals to mass by volume, mass by volume. If you look at this, density is an intensive property. Intensive property, mass is extensive property, volume is also extensive property. So from this definition, you can easily define that when the ratio, if you take the ratio of two extensive property, it becomes intensive in nature. So note down this point, the ratio of of two extensive property, extensive property becomes intensive, becomes intensive, okay? Another example you see, we have a mole fraction, mole fraction, mole fraction what we can write, given number of moles by total moles. So moles are extensive only. So extensive, extensive, this becomes intensive, right? So this formula, this, you know, observation you must keep in mind. If you get confused in the exam, you can think of this way also. Formulages you try to recall from that also you will understand. Clear? No doubt. Okay. One more question. Delta T is intensive or extensive? Change in any variable. Intensive or extensive? Yes, intensive. Change is always intensive. It has nothing to do with the temperature that you have taken. Change if you find out, so it is always intensive in nature. Yeah. Next write down that is thermodynamic functions. Okay. Okay. Write down next. Delta T is intensive. That's what I said. No. Next write down thermodynamic functions. Thermodynamic function, we have two types. We have of two types. First one is state function and the second one is path function. State function is the one which is independent of path. Independent of path. For example, we have pressure, volume, temperature, enthalpy, internal energy, entropy, Gibbs free energy, etc. Path function is it depends upon path. It depends upon, for example, we have heat and work. Suppose you are at this position A. You are supposed at position A and if you want to go to position B, there are infinite number of paths possible. One is this. You can go directly from A to B. One possibility is this. Another possibility is you can roam around and then you can come to this point B. Okay. Another possibility is you can go to some other point and then this and then this. You can go. Means the point I'm trying to make, there are infinite number of paths possible here. If you want to go to, you know, you want to go to Chennai, suppose from Bangalore, you can go to Chennai directly or you can also go to Hyderabad and then Chennai. Depends upon the wish. But the thing is, if you choose the longer path, you have to do more amount of work. More amount of fuel you have to use. That's why the work done and heat required, energy required, it depends upon the path that you choose. But if you talk about the pressure at point A, if it is PA and pressure at B is PB, or for instance, if I say volume is VA, VB, TA, TB is the temperature, no, like it doesn't matter what path you choose. The pressure at B is always PB. It won't change. It does not depend upon the path that you are choosing. That's why these variables depends only upon the state of the, you know, of the system, at what state, at what position the system is. Based on that only, we have the value of PA, PB, pressure, volume, temperature, enthalpy and all. But heat and work, it depends upon what path you are choosing. Hence, these two are path function. This is the state function. Thermodynamic equilibrium. See in thermodynamics, we'll deal with the system which are in thermodynamic equilibrium, always, whether it is mentioned or not. We always consider the system which are in thermodynamic equilibrium. Okay? You won't get any numerical on this, but you should have the understanding of this particular term that what is thermodynamic equilibrium. Correct? Thermodynamic equilibrium is defined when a system is in, when a system is at, when a system is at thermal, chemical, mechanical equilibrium, all three kind of equilibrium, thermal, chemical and mechanical equilibrium, then it is said to be in, then it is said to be in thermodynamic equilibrium. All three equilibriums are there, then thermodynamic equilibrium. We'll have a chapter of equilibrium also, chemical equilibrium and ionic equilibrium, which we'll discuss after this chapter. Okay? There you will have the understanding of what does this equilibrium means. Okay? Briefly, I'll just give you the meaning of this, what is thermal equilibrium, what is chemical equilibrium and all. Right? Thermal equilibrium is the one in which the two object or two system is at the same temperature. Like, for example, if I have this object at 100 degrees Celsius and I have the another object, which is at 10 degrees Celsius, for instance, I'm saying. If you connect these two or if you keep these two in contact, then what happens from 100 degrees Celsius, the heat starts flowing into 10 degrees Celsius because of the difference in temperature. So after some time what happens, both system will be at the same temperature. Right? And when the temperature is same, there is no more heat transfer because the two object or system is now, is at thermal equilibrium. So thermal equilibrium is what it is based upon the temperature. Two system is at the same temperature. They are set to be in thermal equilibrium. Clear? So thermal equilibrium is based upon, based on temperature, constant temperature we have in the two object, two system, chemical equilibrium. When we have constant concentration, if concentration is not changing, constant concentration, concentration changes, but the rate of change is same. Okay. So overall, you know, the concentration is constant only. Last one is mechanical equilibrium. What is mechanical equilibrium? Right? When we have equal pressure, equal pressure, mechanical equilibrium you can understand. You have an object like this and suppose you are trying to pull the object with some force 10 Newton and same amount of force you are applying in the opposite direction 10 Newton. Then we have equal force in the two direction, equal pressure we have. Right? Then this object is said to be in mechanical equilibrium. So when these two, these three equilibrium exist, then the system is said to be in thermodynamic equilibrium and in thermodynamics deals with thermodynamic equilibrium only. Next. Next we have thermodynamic processes. Definition you write down. It is an, what is the process? So it is an operation by which, it is an operation by which a system is changing its state, is changing its state. It denotes the path, denotes the path followed, followed by the system, denotes the path followed by the system while changing the state. If you talk about change over here, change we can also have three types. Change if you see, we have three types we have here. The first one we can say physical change or phase change. Physical change or phase change means what? Solid to liquid conversion, phase change we have. And then we have chemical change and then we have state change. State change means variable is changing, pressure, volume, temperature, right? State change means state variable. It's not the physical state, it's a state variable. So we have this physical change means solid to liquid conversion, liquid to gas, gas to solid. This conversion we have here. This is the change one. Chemical change is mainly deals with the reaction. So reactant to product, the change we have. Reactant to product. And state variable changes means the change in pressure, volume, temperature. So mainly we have this one. The third one is the important one we have here. Copy this down first. Okay. Different processes that we have here, you see, the first process is isothermal process. Isothermal process. Second one is isometric process. Third one is isochoric process. Isochoric process. All these things we have discussed. Then the fourth one is adiabatic process. Adiabatic process. Fifth one is cyclic process. And apart from these five, we have two more processes that is reversible and irreversible. We'll discuss that after this. What is isothermal process? We have constant temperature. Isobaric bar is the unit of pressure. Iso means equal. So we have constant pressure. And the third one isochoric is constant volume. Adiabatic process I have told you. There's no change, exchange of heat. So delta Q is zero for adiabatic process. Cyclic process, initial and final state is same. Initial and final state is same. Okay. For example, you see, this is pressure. This is volume. This is pressure. This is volume. Okay. Now the process, suppose it starts with the point A goes to B, then B to C, C to D and D to A. So it's a cyclic process. Initial and final state is same. Okay. This is also a cyclic process. Obviously you see there's a cyclic process. Right. So cyclic process is the one in which initial and final state is same. Since initial and final state is same over here, so all those variables which are, which are state variables change in all those variables, state variables are zero. Because delta P, if you write, it is PF minus PI. Right. It is final pressure minus initial pressure. But since the final and initial position is same only here. So PF and PI is also equal. And that's why delta P is zero. Similarly, delta V is zero. Delta H is zero. Delta U is zero. Delta T is zero. Right. Delta G is zero. All these change in state variables are zero in cyclic process. Yes. Did you sign it out? Copy this out? Yeah. Finished all of you? Done? Okay. Suppose if pressure volume graph is given, then how do you find out the work done? Just I'm asking. Tell me. You know this? Have you done this in school? No. Right. Okay. Pressure volume graph, if it is given, then directly you can find out the area under the curve. That would be the work done. Okay. Directly. Suppose if I ask you, what is the work done in this process? A to B, B to C, C to D, D to N. Then what you will say? You will find out the area of this. Yeah. P delta V. You'll find out the area of this rectangle. And you'll say, so this is the work done. So that's fine. Okay. But this we can do. We can find out area only if PV graph is given. If PV graph is not given, you cannot find out this because work done is P delta V. So pressure volume graph you must require. So sometimes what happens in the question, instead of PV, they'll give you PT graph or VT graph. So you should know how to convert a PT graph into PV graph or VT graph into PT graph. Means this conversion you should know how to convert one graph into another graph. So let's discuss one example on this. Conversion of graph, graph conversion heading right down. How we'll discuss. We'll discuss after this. This we haven't finished. Reversible, irreversible after this we'll discuss. Okay. Let us finish this first. Right. So the process that we have discussed, no, based on that only we have this. So we'll finish it out first. So suppose here. So this axis is given. It is PT pressure and temperature graph. This is P. This is V. This is PV. This is VP. So this graph is actually given here. Passes through origin constant temperature. This is the graph we have. Okay. And it is given here. The process is going from A to B, A to B. Then we have B to C and C to A. This is a graph given. You need to convert this into the pressure volume graph. Now how do we do this? You see. Could you tell me the process AB? What is this process? AB. What is the name of the process? AB, BC and CA. What is the name of the process? But we didn't, we don't talk about heating over here. AB you see it is PT graph. No, compare this with PV is equals to NRT guys you see. Compare this with PV is equals to NRT. Correct. So we have graph of PNT. Here you see graph of PNT passing through origin. So it is constant volume we have here. Correct. Constant volume. So AB is isochoric. Can we say that AB is isochoric? Similarly, BC is constant temperature. So BC is isothermal and CA is constant pressure. So it is isobaric. Clear? No doubt. Isochoric, isochoric. But what is happening here you see? Pressure is increasing. Pressure is increasing. This you must remember. This is given. Pressure is increasing. B to C we have isothermal but pressure is decreasing. Right? And C to A we have isobaric. Temperature is decreasing. Isn't it? So further if we extend this pressure is increasing. Volume is constant. So temperature will also increase. Temperature will also increase here. Similarly here pressure is decreasing. Process is isothermal. So volume will increase. Volume should increase in this process. And temperature is decreasing. Pressure is constant. So volume should decrease in this process. Can we say that? Is it clear till here? No doubt. Please respond all of you. CLR you can type it. This is one thing. Now we know this PV graph at constant temperature. It goes like this. It is rectangular hyperbola. And we have done this in gaseous state also. The graph goes like this. Isn't it? Can you doubt in this? This is the PV graph we have. Constant temperature. It is it is an isothermal graph. Yes. Constant temperature. So BC process is this. But now the question is question is where we should take the point B? This is point B or this is point B? Could you answer this? Which one is the point B? Top one or the bottom one? Right? You need to hit and trial. Hit and trial you need to apply here. So suppose I am taking this point as B, right? This point as C. Then what happens you see? B to C, the process is expansion or compression. B to C, the process is expansion or compression, expansion. Expansion means volume increases. That is what the thing over here, volume increases. It means our assumption is correct. If you take it other way, just for this one, I am just trying to make you understand. Suppose I am taking B over here and C over here. So B to C is the case of compression. So volume should decrease but here the volume is increasing. It means this our assumption is wrong. Hence the order should be this. B should be here. Right? B should be here. C is here. And this is the case of expansion. No doubt. Yes, tell me. All of you clear? Right? Now the question is where we should take A? Either we should take A this side or this side? That's the question. So again you can give it a try. You can assume it this side and compare the other relationship. So for example, suppose I am assuming A is somewhere here. So what will happen? A to B is this and C to A is this. This is the graph we have. So A to B, what is happening here you see? A to B, the volume is decreasing. Correct? Constant pressure A to B, volume is decreasing. A to B, right? Here you see A to B is constant volume process but volume is not constant here. It means this assumption is wrong. Are you getting my point? If you take A this side, right? A to B should be isochoric constant volume process, right? Which is not coming out to be over here. It is volume is changing over here. That's why this our assumption is again wrong and hence we will take A somewhere here. Here we'll take A. Now what happens? A to B is this, right? A to C is this, correct? So A to B the process, the graph goes like this. A to B, B to C and C to A. Now you can cross check all the data. A to B is isochoric. You see A to B is isochoric constant volume and pressure is increasing, correct? Pressure is increasing. So constant volume, pressure increases. So temperature will also increase. That is what the point we have here. C to A, we have isochoric constant pressure, volume decreases, right? So C to A isochoric volume decreases. So this graph is correct. Did you understand this? Because constant volume we have no. Why linear? Because PV is equals to NRT. One degree equation it is. Tell me, read out. Prakul understood why this linear? All of you understood? Type in please. Yeah. Could you draw VT graph from this? Similarly you need to do. Try this. VT graph you try once. Done. Okay. So VT graph, the line which passes through origin that represents constant temperature line, sorry pressure line, isobaric process it is, right? Isobaric process is C to A. So on this line we have two points A and C. So where we should place this A and C? Should we place C over here and A over here or other way? C above A down. Okay. So we'll write C above A down. Okay. So I'm placing this A over here and C here. How do you understand this? You have to take a guess on it. Okay. You have to take a guess, just a hunch you can say. And then you need to cross check the other things which is coming out to be in line or not. Okay. If it is like fine, if it is coming out to be the other conditions is fine according to your assumption, it means your assumption is correct. Otherwise you have to take the other assumption. Okay. That is how we do this. Suppose I'm taking C over here, A over here. So C to A, C to A is what? C to A is isobaric process. Yes, it is isobaric process passing through origin and the line is this. C to A you see volume is decreasing, right? Volume is decreasing. So temperature will also decrease. So that's what the point we have here. C to A volume decreases. If you take it other way, then it is a case of expansion. Volume increases wrong. Okay. Now, should we take B this side on the top or on the bottom? This side to this side, that is what the question. Suppose if you take B over here, then A to B is the case of expansion. Right. So volume decreases. Volume decreases. You see A to B is a case of expansion. Volume increases, but temperature is constant. But A to B is constant volume process. No, A to B is isocoding. So if you consider B over here, volume won't be constant. Right. That's why this B we need to take over here. B will be somewhere here and C and B will continue. Okay. So this is the graph we have over here. This is B. A to B is this. B to C is this and C to A is this. Now we'll cross check all the data. A to B, you see constant volume, temperature increases. A to B, constant volume, isocodic temperature increases. B to C, constant temperature, volume increases. B to C isothermal, constant temperature, volume increases. So this is the correct VT graph we have from PV we have drawn or PT. So if VT is given, you can convert into PV. If PT is given, you can convert into PV like this and then you can find out the work done in this process. Any doubt in this? Yeah, we'll do one more. Just a second. One more example on this, you see. Okay. The first graph is VT. And this VT graph, you need to convert into PV and PT. The graph that is given is this. This is the graph we have. A point is this. We have A to B, B to C, and then C to A. Try this one. Done? Yeah. A to B is isothermal, correct. B to C is isobaric. Isobaric correct. C to A is isocorrect. Yeah, that's right. Keith, on that side. Okay. So if you draw the graph here, I'll just tell you like the process which is isothermal. Isothermal process is A to B, right? Isothermal process is A to B and that too compression, right? Volume is decreasing. AB is isothermal process. So volume decreases. Volume decreases here. Volume is decreasing. That means pressure increases. That's one thing. Second is B to C. BC is isobaric. Isobaric and volume increases, correct? Volume is increasing, right? Volume is increasing. Pressure is constant. Temperature is also increasing. CA is isocorrect. Isocorrect. Temperature is decreasing and temperature decreasing. Volume constant. Pressure is also decreasing here. This is the information we have with the given graph, correct? Now A to B is isothermal. So this graph will go like this. PV graph if you draw. So A to B, the graph will be like this, okay? But since it is pressure is increasing, so we must have A over here and B somewhere here so that the pressure increases like this, okay? B to C is isocorrect. So isocorrect. B to C is isobaric. So if you take C over here, so pressure won't be constant over here. So I'll take C somewhere here. I'll take C somewhere here and these two points I'll join, right? So we have C over here. So BC. B to C is isobaric, you see? Pressure constant. And C to A is isocoric. Volume constant. Pressure decreases. Pressure decreases. Volume increases. Temperature increases. This is the graph we have PV. Understood? And the PV graph, if I draw here, it goes like this. Same logic you can apply, you will get this. A is here. B is here. C is here and A is here. A, B, C, A. This is the PV graph here. All of you have got this? Any doubt in this? Understood? Yes. So graph conversion is very important. You must take care of this thing. This data, you must have to match with all the processes that you are following. Clear? Okay. So have you done reversible, irreversible process? Reversible and irreversible. So reversible, irreversible process we'll discuss. We'll take a break now because it will take a bit of time to explain that too because after the break we'll start this. Correct? So after the break, we'll start with reversible, irreversible process. We'll resume the session at 6.25. Okay? Take a break now. Yeah, guys. Take a break. Yeah.