 Next heading right down, factors we are done factors affecting the rate of the reaction or the other part in this chapter will see a mechanism of reaction. You know mechanism is what it is the step by step description of the reaction, like what all steps are involved which is the slowest stability and what all intermediate forms stability of intermediates and all. All these description will get from the mechanism of reaction. Correct. So this information you have already I'm directly moving into some examples and the rate expression that we write in this in all these examples. Okay. You see here. If you have a reaction say H two plus I hope I to gives H I. This reaction is a complex reaction. I to converts into to H I overall reaction is this, but this is a complex reaction. So complex reaction we know there are different various number of steps involved into this, it is not single step reaction. So what are the steps involved into this what happens here. The first step the I to iodine decomposes into the atomic form, and this is a fast step reaction we have. And then the hydrogen H to take this atomic iodine and converts into H to I these are intermediates actually. And then this H to I again combines with the another iodine atom and converts into to H I slow. This is RDS the last one. Okay. The molecule the reactant H to an I to H to an I to reacts by these three steps and converts into H I. Overall reaction if I write down will add all these three. And overall reaction I'll write down so overall reaction would be when you add this three, this H to I H to I will get cancer. I, I to I will get cancer. The reaction is H to plus I to gifts to H I. Okay. Now this reaction involves three different steps. Now the graphical representation of these, these three steps is the mechanism of the reaction. Right. So if I write down the rate expression for this reaction, that would be rate constant K into H to into I. Now if I try to express this three reaction in the form of graph. Okay, how do we express it. Do you copy this. Yes. Now we have three steps. So I'll draw. So I'll draw the coordinate axis for the first two steps we are not sure in terms of one term. Third steps we are very sure. Okay. One second. So the x axis we have is the reaction progress or the progress of reaction and y axis is the energy potential energy or energy we can say. Okay. So suppose the energy of the reactant is suppose here at some at this point we have the reactant. Right. It is the energy of the reactant H to plus I to this H to and I to collides with each other, the energy increases, goes to a maxima. Then it decrease. Right. And then again, it forms an intermediate here. The intermediate will write down later. And then again the energy increases is this, and then again the energy increases, and this converts into the product here. The product here is to H I, here is to H I. This is a reaction we have. If you try to understand this how the reaction proceeds any reaction when happens to reactant molecule collides, its energy increases and increases and increases goes to a maximum value at this point will get the activated complex. Okay, this activated complex either converts into an intermediate or product or converts back into the reactant molecule depending upon the condition. That condition will discuss in the next topic. But here you just assume these two collides energy increases forms an activated complex, and then it converts into the reactant sorry, what we say converts into the intermediate which is to I over here the intermediate here is to I I'll just do some correction here. We have taken H 2 I 2, but the reaction is taking place means I 2 is converting into 2 I the first intermediate here. One general graph also I'll draw, then this I can react with H 2 and forms a second intermediate which is H 2 I is H 2 I again reacts with I and converts into this. Okay. Now you'll see one thing here. This energy gap from here to here is the activation energy for first step EA energy of reactant to the activated complex activation energy of first step. This is the activation energy of second step. This is the activation energy of second step. So EA one for the first step, EA two for the second step, and this is the activation energy for the third step EA three EA three third step. So first of all what you know points you can understand here. If I ask you, suppose this graph is given, right? Obviously, if you relate this graph and the reaction that we have written, there are three steps in the reaction. Correct. I want you to look at the reaction as to plus I to give to achieve three steps involved. So three steps were there in the reaction and the number of steps that we had equal number of peaks we get here in the graph number of peaks. Right. Number of peaks first thing number of intermediate that forms. Number of intermediate is is to and that will be equals to the number of peak minus one plus or we can also say the number of steps minus one and number of steps we have so n minus one intermediate will get. Okay, n number of peaks and minus one intermediate you'll get. Okay. One more relation you see which is the most important one here. If you look at this relation of activation energy K is equals to a e to the power minus EA by RT. Obviously, the reaction is taking place at some temperature. Temperature is not a concern number here. But if I ask you as temperature increases, what happens with K? K also increases. I've seen that temperature increases as EA increases as EA decreases the light down activation rate decreases. So rate constant K what increases or decreases increases. Correct. So what we can say that for a given complex reaction, we have n number of steps. All these steps will have its own activation energy as the activation energy increases the rate of the reaction becomes more the reaction becomes fast. Correct. So if I ask you here, which step is the slowest step? What is your answer? The one which has the highest activation energy. Are you getting my point? Yes, sir. Right. So the one which has the highest activation energy is the slowest step. So first step you see what I did here. Yeah, one second, one second. As activation energy decreases, EA decreases. So K decreases. No. Yeah, right only. So if EA is more. No, we should have the third step is the fastest step. Third slowest. Okay, I have drawn the graph in a different pattern. No problem. No problem. The concept is fine. The concept is correct only. Don't get confused. The concept is perfectly correct. So one change is I'll do for make this to make this graph correct. Otherwise, everything we have to change. I'm just taking this is a general graph is considered and not what with respect to his reaction that I've done. Just general graph you assume everything is fine. Just keep just remove that reaction from the mind. Just you see this, you know, reaction, I'll just write down one random reaction just to understand this graph. Okay, I'll give you one general reaction also. A reaction a two plus B two gives to AB. Okay. And in this we have a two gives to a a two gives to a the first step. And suppose this is the slowest step I am assuming. Okay, everything is correct. There's nothing wrong with the concept just you two minutes to give me. Then this a reacts with B to it forms B to a right and then this B to a again reacts with a it forms to AB. This is the three step we have. And this is the fastest step. This is the fastest step. And overall reaction is a two plus B to gives to AB. Now you consider with respect to this we have here initially, we have a two plus B to. Okay, a two plus B to should be the slowest step that's fine. So it is it converts into to a first intermediate, then it converts into B to a another intermediate, and then it converts into to AB the final. All the concepts are same nothing is different. Just I should have taken this activation and it should be the least. This should be the maximum by mistake after on this no problem concept you can understand. Okay, so what I said as activation energy decreases k increases k increases means rate of the reaction increases. So based on this activation energy that you have here for the three step, which one is the slowest step if I tell you this is this is a step one from here to here. Step one from this point to this point it is a step two. And from this point to this point it is a step three. Tell me step one step two step three based on this information which one is the slowest step. The one which has the highest activation energy isn't it correct. So what you can do the slowest step if they ask you in the question by giving you this graph, if they ask you, which one is the slowest step, the one which has the highest activation energy, highest e a, which is for this example, we have a step one. No doubt in this. Correct. Tell me. So sir dissociation of IOT is the slowest step in the previous case. That's what I said. This C just one second. This reaction is correct. Okay. This one is correct. You just leave it here only. It is done here. Finish. Okay, sir. Now you focus on this that's what I really I was trying to draw the graph for S2 I to reaction, but by mistake what I did I took this activation energy is the maximum I should have taken this the minimum. Right, this should be the maximum. But since I have done this graph so for this I have written this, this reaction now you consider this graph for this reaction. Fine. S2 I to let it be if you want I can bring the graph of that also to this. Okay, a to gives to a suppose it is a slowest step reacts to be to fast fast overall reaction is this. So first step is what a to be to converts into to a then to a converts into B to a and then this B to converts into a B. So this graph I have drawn for this reaction. Now you suppose if this graph is given reaction is not given graph is given and they'll ask you which one is the slowest step, what do you do, you'll just see which step has the maximum activation energy, you know, as activation energy decreases k increases reaction becomes faster, correct, because the reactant molecule has to overcome only this much of barrier, it can easily overcome this. But if it has to travel a lot of this difference in energy by collision, it has to reach first this point and then come over this come to this point correct. It's difficult to reach at this point. That's why the step is the slowest step we have. That is what theoretically you can understand from this graph, but mathematical relation we have here as activation energy decreases k increases rate of the reaction increases. So if they ask you which one is the slowest step slowest step is the one which has the highest activation energy that is the step one for this reaction. If I ask you which one is the fastest step fastest step is the one which has minimum activation energy. And that would be what that would be anything between the two for this graph if I say if I drop in this to this looks like the minimum. Okay. So the step three with respect to this graph equation is step three is the fastest step we have. If they ask you the number of steps in this sorry the number of steps in this, you know, in this reaction. So with the graph, the number of steps is nothing but the number of peak we have 123 steps, number of peaks, number of intermediates are two. Any doubt you have to be a one more property we need to discuss here. Any doubt in this tell me. No. Clear. Yes. Now, could you tell me the first step is indoor Exo. The first step is indoor Exo. This is the energy of reactant here and here, the product that you get in the first step which is also which is an intermediate actually, but the energy of intermediate is more than to that of the reactant. Hence, the first step is step one is endothermic with this graph we can say the second step you see the energy of the product of the second step is lesser than that of the reactant. So it is exothermic. Okay, third step is also exothermic, right exothermic. Overall, the, you know, the behavior if they ask you endothermic or exothermic overall the reaction, reactant energy is this product energy is this, then if you look at the difference over here between the reactant and product and we can say, this much of energy Delta H, it will release in the reaction and overall the reaction is exothermic in nature. End out in this. So three, four informations you should know from this graph. Number of steps, that is the number of peaks that is given, which one is slowest step, which one is fastest step that you can understand by looking at the activation energy of the graph. You know, behavior towards the heat, if the product energy is lesser than to that of the reactant energy overall the reaction is exothermic. Each step, we can define or we can understand on the same logic. Okay, energy of this is more than this endothermic less than. Clear, no doubt. You want me to draw the graph of H2, I2 and also H2, I2 you want me to draw H2, I2, I'll draw that. Okay, graph of H2, I2. So I'm assuming what you see I'll go back and see because we know we don't have exact data for this. We know the overall, you know, the energy overall this reaction is exothermic, basically overall it is exothermic. If you know this, I'm telling you this information, correct, exothermic. These two are fast step but we do not know exactly which one is the fastest one that we cannot say. So these two activation energy we cannot compare. Okay, and for this one we can say slowest it is activation energy is maximum. Okay, so let's not focus on the activation energy EA1 and EA2. Right, we don't have idea of this to overall idea we have the reaction exothermic and activation energy EA3 is the maximum we have here. Yes, so with this information I'll draw the graph of H2 I2 you see this. So we have the same coordinate X and Y. So I'm assuming that the energy of reactant is suppose here somewhere here we have energy reactant is this and this is the energy of the reactant. So first step is what is the fastest step correct. So the fastest step we have so suppose it goes like this. Then again it goes like this. And then the third step is this overall it's come down because I know that the graph reaction is exothermic so product energy should be lesser than the energy of the reactant. This is the activation energy of the first step EA1. This is EA2 and this is we have we have EA3. So we start with H2 I2. This is the first intermediate 2 I this is H2 I and this is 2 HI. Third step you see has the maximum activation energy. So this is the slowest step we have with this graph it is the slowest step. This two depending upon activation energy we can say okay. This is the nature of the graph we have for H2 I2. So basically what they do they'll give you the graph like this. Okay, and they can ask you any questions like the three four information that I've given you regarding endothermic exothermic slowest step fastest step. Okay, number of intermediates number of peaks number of steps that you have based on these these three four information they can ask you any question based on the graph. Right, you should know that from the graph what all things we can conclude this graph is for H2 plus I2 gives 2 HI. Any doubt in this. All of you understood please respond quickly. Fine, so we'll take a break now after the break will do more topics we need to discuss a big topic. Okay, both are the last one is quite big. The second last one is not that big. Okay, so after the break will start with the collision theory of reaction, and then we'll see some miscellaneous reaction and how to derive the expression into that. So take a break will start after a break seven or five will start take a break.