 Hello guys. Good morning. Sorry. Good evening. Am I audible? Yeah. Yes guys. So today we are going to start the most easiest chapter of your grade 11 physical chemistry and that is chemical equilibrium. Right? So equilibrium consists of two topics here in grade 11 that is chemical and inic. Inic little bit on the tougher side. Chemical equilibrium is quite easy. So both chapter will do one by one. First we'll finish chemical equilibrium and then we'll start with inic equilibrium. Inic equilibrium is the last chapter of your physical chemistry. Okay. And then we'll move it to organic. So I think we have a two. Two class will take not more than two. Two class will finish it. Do you have an exam? Okay. Any information, any info if you get regarding exams, let us know. Any one of us or you put it in the group better so that we can plan things accordingly. Probably haven't done anything yet. We are about to start. I said just we are going to start chemical equilibrium. That is it. So, should we start the story? Yes. Tell me. Did you understand what I said? How many of you understood? Wait, mother. Okay. Right. So, okay, mother, this is a different chapter. Okay. Thermodynamics is done. It's a different chapter. Yeah. I said that only. Yes, correct. Okay. Right. You see, like I said, this chapter is the most easiest chapter. Okay. Heading all of you right down. First of all, chemical equilibrium. So this chapter is all about equilibrium in chemical reaction. Right. Like we'll talk about equilibrium in chemical reaction. So how equilibrium exists in chemical reaction? What are the term associated with with equilibrium? Or we also see the effect of various factors on the equilibrium condition, like what will be the effect of temperature, what will be the effect of pressure, what will be the effect of volume, many other factors. Right. So first of all, this chapter, like I said, is all about equilibrium. So first of all, you need to understand what is equilibrium. Correct. So what do you know about equilibrium top itself? What is an equilibrium? An object is said to be in equilibrium when an object is said to be in equilibrium. What is the condition for equilibrium state? Okay. There's no net change in the system. Right. Change is occurring, but we cannot observe the net change. Net change is zero. Okay. Like you see thermodynamics, we are finished. Right. Two objects at same temperature. If you have two objects at same temperature, right, then there's no flow of current. Sorry. Heat. Temperature T, temperature T, there's no flow of heat. No flow of heat. And we say the two objects is at what equilibrium? Thermal equilibrium. Right. If the temperature difference is there, the heat flows from high temperature to low temperature till the temperature becomes equal. Correct. So this is thermal equilibrium we have. So you see for equilibrium condition, we must have two opposing factors. Isn't it? Suppose another example if I take, if you have an object placed at a table, for example, if you have an object placed at a table, if you apply a force from this direction, an equal amount of force, if you apply from this direction, then what happens? There's no net movement in the block. Right. It will be static. There's no net movement. And we say, and we say the system or the block is at equilibrium. Net force is zero. F net is net force is zero. Right. So you see for equilibrium condition, if you remove this force, then you are pushing the block from this side and the block will move towards the right. If, if, you know, we are assuming the condition that the force is, you know, good enough to overcome the frictional force that we have over here. Can we say that? If you remove the right wall of force, this force, if you remove, then the block will move towards the right. Since we are applying the force from this direction, right? If this force is, or can overcome the, the frictional force, isn't it? So this is what you see. The two factor, if you see over here, the two example, equilibrium requires two opposing factor. Without opposing factor, equilibrium is not possible. Right. So I hope you understand the anyways, you know, what is equilibrium, but we need to consider, understand all these terms with respect to a chemical reaction. Okay. Before going into the chemical reaction, I let me tell you, there are two types of equilibrium also, two types of equilibrium. One is static equilibrium. One is static equilibrium. You won't get any question in this classification, but you should know the term actually, right? Static equilibrium. And the second one is dynamic equilibrium. Static and dynamic equilibrium. Static equilibrium, the example we have here, block on the table. This is, there's no net motion here. There's no motion impact. The block is static at one position. There's no, there's no motion at all. This equilibrium is a static equilibrium. So no motion or no movement. You are sitting on the chair, right? I hope not at the bed lying on the bed and in the glass. Yes. So if you're sitting on the chair, static at one position, there's no net force, you are at the static equilibrium, right? No movement. F net, net force is zero. That is the condition of static equilibrium. Dynamic equilibrium is what I will just do this one example. You will understand what is dynamic equilibrium. Suppose we have a, a container, a bucket, whatever you can assume. Suppose this is the bucket we have. And in this, the water is present in this. This is the water level we have. This is the water level we have. Now if you try to increase the water level, right? So you'll put some water, this is the inlet. Water inlet, you're filling water into this. This is the inlet. But what you see, you're filling up water into this tank, but the water level is not rising here. Why not? It doesn't rise on inspection. What do you find? You find that there's a hole here in the bottom and the water is flowing out at the same time, right? You're, you're, you know, filling the water here. There's the inlet point and there's the outlet point, right? From where the water is going out. So the water level does not rise. Only one condition we have here for this, that is the rate of inlet is equals to what? Is equals to the rate of outlet? Can we say that? The rate at which the water is filling into the tank with the same day to day, if it is going out, then there is no rise in the water level. Yes or no? Can we say that? Yes. So what happens here? There's a continuous flow. Still the water level is static, continuous flow. So the molecules position is continuously changing. Suppose one molecule is here. It won't be here for so long, right? It will change its position slowly and it is possible that it will come out from this outlet. Yes or no? So the molecules position is changing at every moment, but still the water level is static, constant. It is not changing. This kind of equilibrium, we call it as dynamic equilibrium. Understood any doubt in this? Dynamic equilibrium. Any doubt? No? Okay. So with respect to equilibrium, with respect to equilibrium, yeah, I'll go back one second. Yeah, you have to note it down. Whatever I write on the board, plus whatever I say, everything you should write down. Okay, if something is not required, I will let you know that don't write this. It's not required. Mother, copy this down. You won't be able to keep this in the manual pocket. Mother finished. It's in Jan, Saswath. Exact date, not sure right now, but it's Jan. How many of you are attending BIO session for KAPI? Sunday, how the classes are going on? Or a straight back filming? How the classes you are finding in? Are you understanding the concept? See, there are two things. Okay, fast. See, the thing is, you know, you need to complete the portions also on time. That's why he is going a bit fast, but you can ask him to slow down a bit. That's not a problem. If you are not able to write down the notes, if you're finding it difficult, when you ask him, sir, you can wait like you stopped me here. Similarly, you can ask him also. That's not a problem. Another thing you can push him to any level as far as the concept is concerned. Let me tell you this. Okay, he is one of my good friends. Okay, I know him personally. I won't take his name because he is associated somewhere else, not in Bangalore. Okay, we were, we both were there in a quota together. We were working together in quota and career point. Right. So he's a good friend of mine, very good knowledge, very, you can say knowledge is very fine. He himself is a doctor, finished his BDS from a government college in Delhi. Right. So concept wise is very rich. You can push him to any level. If you, if you do not understand the concept, you can push him to any level. Okay, so don't get shy, must interact in the class. All of you. Okay. Okay. So a little bit fast. I can understand because the syllabus is too much. You know, okay, if your syllabus is not defined, so there are so many things we need to cover. That's why he is probably going a bit fast. But yes, notes are very important. You must write it down. If you're not able to, then ask him to just wait for a while. We'll write down the notes. Okay. Yeah. So, yes, so dynamic in dynamic equilibrium you understood here that the molecules position is changing continuously. Right. And there's a continuous flow, still the level of water is static here. That is dynamic. Okay. Now you see, if you observe the two things here for equilibrium condition, one thing is for sure that there are two opposing factors like you see here inlet and outlet together. Right. If force from the left and from the right also it is there. So for any equilibrium, we must have two opposing factors. Okay. Now if you talk about chemical equilibrium, means equilibrium in chemical reaction, equilibrium in chemical reaction. If you talk about the equilibrium condition in chemical reaction, this chemical reaction must be what must be reversible in nature. Must be reversible in nature. Why I tell you reversible in nature because reversible reaction, what is the, you know, definition of reversible reaction? Suppose I'm writing down your A gives B. This is the sign of reversible reaction to half headed arrow towards the product and then towards the reactant like this. Okay. This is the sign of what reversible reaction because you see reversible reaction is the reaction which proceeds in both direction. A say B and B to A also it's possible. So two opposing factor we have. Right. That's why the equilibrium possible only in reversible reaction. Right. So both way the reaction proceeds reactant to product and product to react both way the reaction proceeds and hence, you know, in this type of reaction equilibrium exist. If there is only one way reaction A to B, then equilibrium is not possible in those kinds of reactions. So one is like bi-directional reaction, which is this and one is monodirectional reaction, which is irreversible reaction. So if you talk about the classification of reaction, one of the classification is this, that the classification based on the direction of the reaction. See this classification based on the direction of reaction, right. Two types of reaction we have here reversible and the second one is irreversible reaction, irreversible reaction. Like I said, reversible reactions are those reactions in which the reaction proceeds in both directions. So it is bi-directional in nature and this one is monodirectional represented by an arrow from reactant to product. Like for example, A gives B. This is irreversible reaction. This reversible reaction is represented by this half added arrow in opposite direction. Like you see here, A gives B this one. This is reversible reaction. So equilibrium exists only in a reversible reaction. Here, since it is monodirectional, so no equilibrium. Okay. We are talking about chemical equilibrium. Hence, in this chapter, we are mainly going to deal with reversible reaction. Understood? There are different different classification here. Okay. Like based on direction, we have these two types of reaction. Based on speed, we have three types of reaction, very fast, slow, moderate speed reaction. One second, one second. Reversible reaction, you know, there's no condition. Thing is, you should know that this particular reaction is reversible. Once you practice, you will understand. Like Haber's process, Haber's process N2 plus 3S2 gives 2NH3. That is a reversible reaction. So you should know few examples of reversible reaction. Okay. We'll discuss some examples here. Why reversible or irreversible? That is completely on reaction condition. Okay. We don't have any control on that. If suppose A gives B and B also has tendency to divert back into A, then it is a reversible reaction. So this tendency depends upon the nature of the molecules there plus the condition of the reaction. Okay. Yeah. So that's one thing. So like I said, classification of reaction, we have many different types of classification direction wise. We have this speed wise, we have very fast, very slow and moderate speed reaction. Phase wise, we have homogeneous and heterogeneous reaction. Homogeneous reactions are those in which, you know, all phases are same. Only one phase present heterogeneous more than one phase. Okay. Like this, we have various different classification of reactions. Okay. But here we have done only direction based because we have to understand the reversible reaction. No, we cannot make irreversible into reversible reaction. Generally, it is, you know, not possible or very difficult to do because if it is possible, then there is no point of talking about this. Right. We change the condition and product will convert into a reactive. Right. So reversible reaction, we have one set of reaction in reversible, another set in reversible reaction under any circumstances, you cannot convert back into, you know, go back into the reaction. Right. If it is there, maybe some very drastic condition if it is required, maybe at that high temperature and high pressure or low pressure, low temperature, we can talk about hypothetically, but it is possible at very high temperature that particular molecule does not exist. It may get vaporized or freeze or anything is possible. Right. That's why we have the, yes, water to vapor is a reversible reaction. It's a reversible process basically, where water, obviously you see water goes into vapor form when you have, you know, hot water in the glass, put your hand and cover it up properly. The vapor condense at your head. Right. It converts into liquid again. So it is reversible reaction, reversible process. Understood. Yeah. So why reversible? Why equilibrium condition or equilibrium exists only in reversible reaction? Because for equilibrium, what we need, what we need for equilibrium to opposing what factors, two opposing factors. So here you see A is going into B, but B is also going into A. We are the opposing factors we have. Here we don't have such factor. Right. That's why the equilibrium possible only in reversible reaction. Second thing you must understand, which is understood basically, but I'll tell you, since we are doing this first time, you should know this fact. Equilibrium possible whenever, when the reaction is taking place in a closed container, the container must be closed. If it is not closed, then it is possible that some of the species escapes into that atmosphere. And in that case, we will never have equilibrium condition. Mass must be constant, total mass. Yes, no. Close container for equilibrium. So it is, you know, generally it is not mentioned in any question, but you have to consider this only close container. If equilibrium we are talking about. Yes. Fine. No doubt. Okay. Now you see. Yes. Next one. Suppose we have this reaction. We'll take the reference of this only to understand the concept here. A gives B. When A is converting into B, this we call it as forward reaction, forward reaction. When B is converting into A backward, this is backward reaction. No, it's not possible. For equilibrium, we always have close container, any reaction, because for equilibrium mass must be constant. Mass must be constant. It is something like, suppose you have a system, if I try to explain this thing in terms of thermodynamics, you have a system. Correct. Isolated. Energy is not going out under any condition, rigid wall. Then if A converts into B, a reaction we have into this, there's no exchange of energy with surroundings. So can we say the total energy of A equals total energy of B at any time? Can we say that? Energy balance we can do because the wall is rigid. No work is done on the system or by the system. Wall is insulated also. So energy will not go into the atmosphere. It will be within the system only. So if A is converting into B, so at any point of time we can write, the energy of A equals to the energy of B. Why? Because the total energy is constant. There's no exchange possible here. Total energy is constant and hence this conservation we have. Similarly, if the reaction is taking place, so for equilibrium, the total mass or amount must be constant. If it is escaping into the atmosphere by any means, then total mass won't be constant. We cannot have the equilibrium condition. Understood? This is also the necessary condition we have. Necessary condition is this. Okay. What solids means what? Solids means what? And then also it's fine. For anything, a reaction must be in a closed container. Failure does not matter. If you say H2O liquid converts into H2O gas or vapor, the phase is changing over there. That's an equilibrium reaction. And don't get confused at water boiling. It goes into that atmosphere. How it is equilibrium? What I'm telling you, that reversible reaction, the process is reversible there. When you have the reversible process in a closed container, then equilibrium condition we can achieve. But reversible reaction in open container, equilibrium is not possible. That's what I'm telling you. Okay. So we are talking about here two reactions forward and backward. Okay. So what happens here you see, again I'll write on this, at initially we have only reactant present. Right. So initially only reactant present. If the reaction starts, then reactant starts converting into product. Suppose we have a container, closed container in which I have taken A, the reactant and some concentration of A we have here. Obviously we have some condition also, the reaction condition. Under this condition, we have taken a certain concentration of A. When the reaction starts after some time what we see, after some time what we see that the concentration of A is decreasing and we are getting some product. Yes or no? B. So since A is converting into B. So what we can say the concentration of A decreases with time and concentration of B increases with time. Yes or no? Because initially there's no B for 0. But when the time proceeds, reaction proceeds, concentration of B is increasing because some amount of A is converting into B. It is closed vessel, so nothing is going out into that atmosphere. Within the vessel only one part of A converts into B. Yes. So we can say as the reaction proceeds, as reaction proceeds the concentration of the concentration of reactant decreases and that of product increases. Isn't it agreed? So yeah. So you see, we are going to understand one more term over here that is the rate, rate of reaction. Why we are discussing this in a while you'll understand any reactant. I'm just taking this, A is a reactant, B is a product. Any reactant, any product. Here this is A left hand side, you always have reactant hurry and that's assumption we have on this, reactant and product. Now tell me, what do you understand by the term rate? What is rate per unit time? So rate is what? Rate is change in any quantity per unit time. Correct? Like for example, velocity is what? Rate of change of, rate of change of displacement, right? So displacement divided by time is velocity, isn't it? So when I say rate of change of displacement, it means our calculation is displacement divided by time is velocity. Speed is what? Rate of change of distance means distance per unit time is a speed. What is acceleration? What is acceleration? Rate of change of, rate of change of velocity, right? So velocity by time basically it is, right? That is acceleration. So when you see here, whenever I say rate, it means we are doing per unit time calculation. If you are talking about rate of reaction, then it would be, for rate of reaction, it is the rate of change of concentration. It is either the rate of change of concentration, rate of change of concentration or pressure. Pressure we use when we have gaseous, you know, reaction. In case of gaseous reaction, we use pressure. Otherwise, concentration we talk about. No doubt in this. When you talk about the rate of any reaction, so here that quantity is concentration or pressure. We talk about this forward and backward reaction. So next slide down, rate of, next slide, just heading you right down, forward reaction. Forward reaction is reactant is converting into product. Once again, mother, once again. Reactant is converting into product. And when the reactant is converting into product, can we say the rate of, rate of forward reaction, forward reaction decreases, decreases with time. Is it correct? Can we say that? Rate of forward reaction decreases with time because concentration is decreasing, right? So rate for any reaction you see, rate is directly proportional to, or not directly, you write down, right on proportional to concentration. We have few things that we won't discuss now. Proportional to concentration. We can have any terms over here, but more or less, this is not the only thing. We can have concentration is square also. We can have root over the constant, anything is possible. But yes, this you can understand just for now. So in this bracket, I'll write down here, one star mark. This is star mark of concentration, not always. Means we do not have linear relation always. We can have other relation also possible, but with concentration rate either increase or decrease. No, no, that's not the reason. Let it be. Okay. I won't discuss all these things here. We have one more chapter of chemical reaction that's chemical kinetics. Okay. There we'll exactly understand the relation of rate and concentration. Okay. We have one term over there, order that you need to understand. Let it be. Let's not go with, they're not required here in this chapter. Usually what happens is, since the reactant is converting into product, right? So concentration of reactant decreases, hence the rate of forward reaction also decreases. So could you tell me at what point the rate of forward reaction is maximum? Yes. Initial point, the point where the reaction is about to start. They're the rate, beginning of the reaction. Very good. So there's a rate of the forward reaction is maximum. Can we write down this opposite thing for backward reaction? Right? So for backward reaction, what happens? Backward reaction, we can say the product is converting into reactant, just opposite. So rate of forward reaction is what? Sorry. Rate of backward reaction is what increases with time because the product is forming. The product is forming, right? Rate of forward reaction, I am writing it down as RF, rate of forward reaction. Rate of backward reaction is RP. Why it will decrease? Initially, we have only, there's no product present. Initially, we have only reacted. See, you have alitya. There's a law for this. Okay. We'll discuss that. But one simple logic you just think. If you have a very high concentration of reactant, then it will have high tendency to convert into product. No. Yes. Initially, when the concentration is too high, then the conversion rate will also be high. It will convert fast. Right? Reaction will be more, more molecules, more will be collision, more will be the rate and hence the conversion is more. Yes, sir, you're audible. What happened in this time? Where is this? Some things happened. This is a convince. It's fine now. So more amount of reactant, conversion rate will be more. Hence it is actually proportional. Right? I'm telling you, it is not always directly proportional. But it is not always actually proportional. You can have, you can have this thing also that the rate is directly proportional to concentration square. Rate is very proportional to root over of concentration. Rate is directly proportional to concentration itself. Anything is possible here. But let's not go or discuss all these things. It is there in chemical kinetics that we'll discuss later. You can just here understand rate increases with increase in concentration, decreases with decrease in concentration. Clear? Yes. Okay. So we have this. See what happens as the reaction proceeds, as the reaction proceeds, we can say the rate of forward reaction decreases and the rate of backward reaction increases. So we'll get a point here where the rate of forward equals to the rate of backward. Right? Obviously, one is decreasing, other one is increasing. So we'll get a point where the rate of forward equals to the rate of backward. It is something like this. Rate of forward reaction is maximum initially and rate of backward reaction is minimum. Right? So slowly it is going down decreasing and it is increasing. Right? At some point of time, the rate becomes equal forward and backward. This is the condition we have. This condition is the condition of equilibrium. Can you doubt? What is the condition of equilibrium? The condition is rate of forward reaction must equals to the rate of backward reaction. Correct? Okay. Rate of forward must equals to the rate of backward reaction. So two points we have here, condition of equilibrium. The first one is rate of forward equals to rate of backward and this is only possible when the reaction is taking place in is in closed container. Is the, if the reaction is not in closed container, this reaction, this condition you never get and hence the reaction equilibrium is not possible. One more very important understanding of equilibrium you must have but just again, I don't get how the rate of backward reaction is increasing. It will increase. No, you see. You think like this, Anurag. You think like this. We have A to B, correct? When time T is equals to zero where the reaction is about to start, we have only A, concentration of A is CA and there's no B present. When B is not there, there's no tendency to convert into A. As the reaction starts, CA minus C, some part of A converts into B, this becomes C. The moment it starts forming, its tendency to convert back into reactant A will increase, will be more. And hence we say as the time to proceed, the rate of backward reaction increases because the concentration of B is increasing. Means what it is simultaneously happening. What is happening? A is going into B and B is going into A. So initially, rate of backward reaction, if you see, it is lesser than to that of forward reaction. But slowly, rate of forward reaction is decreasing and rate of backward reaction is increasing. That means rate of conversion of A into B is gradually decreasing, rate of conversion of B into A gradually decreasing. So you'll get a point, a time where the rate becomes equal. Is it clear? Yes, that's what I'm going to discuss this point here, one second. So we're talking about equilibrium here, correct. So what happens when the equilibrium is established? Okay, all of you listen to me very carefully. Equilibrium is established, then what happens? Rate of this reaction, RF, rate of this RF and rate of this reaction, RB, this becomes equal, right? RF equals to RB. I am not saying that the reaction is not happening now or the reaction stops at this condition. What I am saying? I am saying at equilibrium, the rate becomes equal. Means the reaction is, reaction is going on, reaction does not stop at equilibrium. But the rate of the forward and backward reaction is equal. Means the rate at which A is converting into B and B is converting into A becomes equal. That is the equilibrium condition. I do not, I am not saying that the reaction is not happening once the equilibrium is achieved. Reaction is continuously going on, even at equilibrium also. But the only difference is once the equilibrium achieved, if you do not disturb the reaction, then the reaction proceeds with equal rate, rate of forward and rate of backward. Is it clear? So these are the few properties you must keep in mind with respect to equilibrium, right down. The reaction never stops at equilibrium. It proceeds with equal rate in both directions. This is the first property we have. Do not get confused. They will ask you questions on this. Theatrical questions also they fail. Not always, Anurag, once again. I am coming to that point also, once again. That is the one point. When the reaction proceeds with equal rate, then what we can say, we can say there is no net change in the concentration of reactant or product. No net change in the concentration of, of a reactant or product. Is it fine? Did you understand this point? There is no net change. Suppose some part of A converts into B at equilibrium. The same part of B will also convert into A. So concentration will be constant of A and B. Is it clear? Okay. So it is third point also you can write. The concentration of reactant and product is constant. Reactant and product is constant. Again, you see, but I will go back once again. Okay. With respect to this reaction we are talking about. So what I said here, concentration of reactant and product is constant. I am saying constant, not equal. Okay. So all three possibilities we have, as far as the concentration is concerned, we can have C A, the concentration of A equals, I will write it on this page just a second. At equilibrium, we have all the possibility. What possibility? That concentration of A can be equal to the concentration of B. Concentration of A could be more than the concentration of B. Concentration of A could be less than the concentration of B. All three conditions are possible. Right. Constant means, does not mean it's equal. Rate is constant. Right. Rate becomes equal, not concentration. Suppose in two seconds, if I take this example, in two seconds, the concentration is changing from 8 to 4. So what is the rate here? What is the rate here? It is the difference of this 4 divided by 2. It is 2 molar per second. Can we say the rate? Yes. So we can have this value 2 for any concentration. Like you see, we can also say that if it is changing from 12 to 8, 12 to 8 if it is changing in two seconds, then also the rate is what? Rate is 2 molar per second only. Means at two different concentrations for a given time, we can have the same rate. Right. It means that we do not have a specific condition for concentration. We can have any three conditions possible. Is it clear? Did you understand this? So in chemical reaction, what kind of equilibrium is it? What kind of equilibrium is this in a chemical reaction? Dynamic or static? What kind of equilibrium is this? Dynamic or static? It is dynamic equilibrium because the reaction never stops. Okay. It is a dynamic equilibrium. Each and every point is clear. Is there any doubt? Clear? Everyone respond please. It's clear. Now you see all these information that we had discussed just now, based on this, how they frame the question in J. Okay. We will see that. I am going to draw few graphs here. You have to tell me that which graph is possible for any equilibrium condition. Right. This is rate. This is time. This is rate. This is time. Look at this graph. First of all, you tell me which graph represents the forward reaction? Which graphs represent the backward reaction? One and two. Which one is forward? Which one is backward? One is forward and two is backward. Right. Because we know forward rate decreases. So one represents forward and two represents backward. Okay. One thing is correct. Now, this is the RF rate of forward reaction and this is RB, the rate of backward reaction. This is also RF. This is also RB. And this is also RF. This is also RB. Tell me, which of these three graphs represents the equilibrium state or equilibrium graph represents the equilibrium state? First, second or third? First graph, first and third. See the condition for equilibrium is what? The condition for equilibrium is rate of forward reaction equals to the rate of backward reaction. This is the condition we have. So this is true. This is true if this condition is at here. So this graph represents the equilibrium state. But in the other two graphs, you see, the rate is not equal. Correct. Rate is not equal. It is becoming constant after some time. The rate is becoming constant after some time, but it is not equal. Hence, these two graphs does not represent the equilibrium state. First and second represent equilibrium. But the reaction does not stop at this point. No. It continues. Right. Here you see when it becomes equal, then it will go with the equal rate like this. It is the equilibrium state. If it is equilibrium, the reaction should stop over here. Correct. So this is not, the first two graph does not represent the equilibrium state. Correct. One more thing you must keep in mind. Technically, this graph is not possible because at any instant, the rate cannot exceed this particular line, this particular value. Right. Because it is the maximum rate of any reaction we have, isn't it? This is the maximum rate, the initial concentration of reaction. So this graph will never exceed this line. Okay. So let's rate we correct this. I have purposely given this. So this graph, you must take care of. It won't, it will never exceed this particular line, which is the maximum rate. Clear. No doubt. Okay. So only this one is correct. Okay. Now, three more graphs we have here. Tell me, which graph represents the equilibrium state? Okay. See. So obviously, if you have the graph like this, okay, you see, for this one, yes, for this one, you see the concentration is equal. Right. Concentration is equal. So for this one, we can say it is CA is equals to CB. Reference is that reaction only we are taking. And that is the condition of the equilibrium. This one is fine equilibrium state. Here what we have, CA is greater than CB. This one is also fine equilibrium. We know this condition is also possible. This reaction is also, this graph is also fine. For this one purposely, I have given this graph, which is above this concentration line. So if this is the graph we have, then this is not possible because the concentration of product can never exceed the concentration of the reactant given. Okay. If the initial concentration is zero, right. So purposely I have given this. So if I make one change over here, suppose the graph goes like this, okay, it becomes constant at some point. So for this one, we can say what? For this one, it is CB greater than CA. So this graph is also possible. So for this one, if concentration is the excess, then all three, all three graphs represents equilibrium state. We are talking about concentration matter. It's not mole. Mole is not concentration. Mole per liter we are talking about. It's not possible. No, that is not possible. No, Hariharan. The reactant won't convert into product completely because before that only you will have the equilibrium state and then the rate will be equal. I have taken this example stress, you see. Suppose you have the constant change in constant A to B, suppose we have here. You are starting with, suppose 20 is the concentration molar concentration you started with. It is zero initially. Then at, it is T is equals to, let me just write this down properly. It is T is equals to zero. This is the state we have. What we observe at time T is equals to two second. The concentration of A becomes 15 and rest is B that is five. So what is the rate of the reaction? Tell me with respect to A, the rate is what? It is five by two. So I'll take one value so that we can cancel it out and we'll have a better, you know, this thing. I'm assuming this as 20 to 16 molar. I am assuming and this one becomes the rest, which is four. Some hypothetical data I am taking, correct? So what is the rate here with respect to A? The rate is, is it two? Can we say? So let's tell me. Yes. Okay. The reaction continues, right? So at T is equals to four second, this becomes 12 molar. So what is this? This would be eight, isn't it? So for this concentration, obviously the concentration is different, it was 20 and 60. Now from 16 it becomes 12, right? So what is the rate for this data? For this data, what is the rate? Shreyas, tell me. It is two. Again, for the next two seconds. Yes. So rate is equal or not at two different concentration. So rate is what? It is changed divided by time. Change in concentration divided by time. The rate is two, you can get from any possible, you know, concentration like 100 to 15 in 25 seconds. Rate is two, right? If you have 10 to, like, suppose we have, we have eight to four in two seconds, rate is two. So for any value of concentration, we can have the same rate. That's why we have all three possibilities. I hope you understood with this, right? So concentration could be anything because we need to find out the rate that is difference in concentration divided by time. So I think you understood all of you, clear? Yes, you can say that if slope is equal, the rate is equal because slope is dc by dt only, right? So dc by dt is nothing but concentration per unit time. That is rate. You can say that. Any doubt? So based on the graph, they asked this question. Okay. So like, students get confused over here. Which one? This is what you're talking about, Namta, the first one. See, it is a, it is a condition when the concentration of B is more than that of A. That is also possible, right? See here. A gives 2B. We have this reaction. Initially, it is 10 at time t is equals to zero. At time t is equals to three. Suppose it becomes nine. Oh, sorry. Suppose it becomes one. Tell me the rate with respect to eight. Namrata, what is the rate? No, no, no, wait, wait. See, 10 to one. Change in concentration is what? 10 minus one? 10 minus one? Change in concentration? Divided by the time required to produce this change. Which is three? Fine. Three you got. Yes. It's correct? No? Yes. So what is the concentration of A at time three? At time t is equals to three. What is the concentration of A at t is equals to three? What is the concentration of A at t is equals to three? No, it's not. Nine, though, it's certainly reacted. Nine reacts. One is left. No. This is what which is left. So what is the concentration of A at time t is equals to three? That is one. So how many reacts? How many reacts? Nine. So one mole of A gives two mole of B. Since nine mole reacts, so nine mole of A gives how much mole of B? Tell. Speak up. One mole gives two. Since nine mole reacts, so nine mole gets how much? Eighteen. So this is the molarity of B you will get. You see the concentration of A is one and that of B is eighteen. It is more, no? So it depends upon the extortionometric coefficient. So in general, we need to understand that all three conditions are possible. If it one is to one ratio, if you take, then also it's fine. Nine mole reacts. One gives one. So nine gives nine. Understood? That's why I said that all three conditions are possible at equilibrium. You can ask one more thing here. Like, so it was zero initially. It becomes eighteen. So rate should be eighteen minus zero by three to six. Right? Yes or no? Concentrate here. It's very important. Is this a genuine question? Because at equilibrium, the rate must be equal. I'm taking this rate of forward is three, but this rate, what we are getting? Time is three seconds only for both the reaction. So eighteen minus zero by three is six we are getting. So you can also say it is not the equilibrium state. Yes. Okay. Are you alive? All of you? Is this a genuine question? Could you answer this question? What is happening over here? I said what Aditya, that for three seconds, whatever the change is happening is for three seconds. Means for B, also the time is three seconds. For A, also the time is three seconds. If it is the equilibrium state, then rate of A must be equals to B. Rate of disappearance of A must be equals rate of appearance of B. So rate of A is what? That is what we have calculated. Three. Ten minus one divided by three. Similarly, if you find out the rate of B, it would be what? Difference is eighteen divided by three is six. Yes. So rate is not equal. It is not an equilibrium state. Can we say that? Yes. Could you explain this? Yesterday as I got your point, could you explain this? What is happening here? No, rate. Rate is equal here. Okay. Let's not confuse here. This is okay. See, to understand this, you need to know the rate expression. For B, the rate expression would be half of the change in concentration divided by the time taken for this concentration. This two comes over here in the denominator. Hence, you see, it is three only we are getting. So how this rate expression will write, that's not a question for this chapter. Let me tell you this thing. Okay. I said this because later on, I think you may have this doubt. So here, though, eight by three, it is six. So how the rate is equal? How did you explain this as an equilibrium state? Because rate is six and three, we are getting over here. Hence, to avoid this confusion, I have taken this question. But for this question, let me tell you rate expression to write down the rate expression is not the question over here. You are not going to have any questions based on the rate expression. How to write down the rate expression with respect to reacting that product, we have a separate chapter for this that is chemical kinetics that will do in grade 12. Right. So here, let's not discuss about the rate expression. Okay. It's not required over here, but yes, the expression is this. Okay. It's not that tough. You will understand once we discuss this, but yes, the thing is like this. Okay. Can we move on? Did you understand this? Can you move on? Yes, all of you. Namrata, any doubt? Okay. So we have discussed this rate. I hope you understood the concept of rate and any questions, graphical or theoretical questions based on rate and concentration relation, you could solve from this. Okay. Yeah. Give me a second. I'm just coming.