 how to find out the expression, everything we have discussed. Next, we need to discuss here the factors affecting the rate of reaction, the rate of reaction. The factors which affects the rate of reactions are right on the nature of reactant and product, nature of reactant and product, concentration of reactant. So concentration, then we can have a relation of concentration, pressure and volume also. So that also we can understand here. Concentration is inversely proportional to volume. This relation we have and concentration and pressure are directly proportional. So these two also we can relate here. Third point we have, temperature. Fourth one is catalyst. Fifth one is effect of sunlight. This we are not going to discuss. I'll just write down here. UV radiation also we can write here. pH of the medium, effect of electric and magnetic field. I have just written this one, this one and this one. We are not going to discuss, not that important. This is there when the polar molecules are involved. So these three cases depends upon that type of reaction. So when polar molecules are involved, this is a factor we have. pH of the reaction is a factor when we have acid-base reaction. Otherwise this is not a medium, acid-base reaction. Effect of sunlight, again, we have when the bond dissociation is possible in presence of sunlight like coordination and all. In those kind of reaction, effect of sunlight is a factor. But more important one is these four. And these four we are going to discuss in this chapter. The first one I write down, the nature of reactant and product. Nature of reactant and product. So first thing in this, the physical state. This overall, if you see among the four, this one is the least important. You won't get question on this. Physical state, the rate of reaction you see, the rate of reaction is observed to be maximum in gaseous state. Then we have liquid and then we have solid. Frequent collision is there because of the least intermolecular force. And hence the rate of reaction is maximum. Okay, second one in this we have the surface area of reactant. The surface area of reactant. The size decreases, surface area increases. The contact surface area we are talking about, right? The contact surface area or the surface area increases. And when surface area increases, we'll have more rate of reaction. Even reaction is nothing but the collision of the two reactant molecules. So when the two reactant molecules collides, when the surface, the contact surface area is more, the rate of reaction will be more. So basically we can write ROR is directly proportional to surface area. Okay, third one, chemical nature of the reactant in product. Or we can write on stability. Obviously when reactant is more stable, it has less tendency to go under reaction, right? Hence rate of the reaction decreases. So rate of reaction, inversely proportional to the stability of reactant and directly proportional to the stability of product. More stable product can form easily, more will be the rate of reaction in that case. Now the second point that is concentration, second factor is the most important one. And maximum part of this chapter, the first part that we have, means the second part like I just said, the mechanism part, right? The mechanism of the reaction. So the first part in this chapter that we have, it is based upon the concentration thing, right? So the concentration of the reactant, this factor is the most important factor we have. So the next second, second factor we write on, the second one is the concentration. See, we know concentration and volume are inversely proportional and volume are inversely proportional, right? So what happens if concentration, this region we have a concentration in volume. So change in volume also affects the rate of the reaction, right? That is also we can say, okay? We know concentration and rate are directly proportional. We have that expression of rate of reaction and all we have seen that. So concentration and rate are directly proportional, but it also depends upon the relation of concentration and rate, whether it is directly proportional or what, it also depends upon the order of the reaction, okay? So the relation of rate and concentration, I'm not going into it now, okay? So in general, what we say, that concentration and rate are related to each other, volume and rate are also related, but the behavior of rate of the reaction with the change in volume and with the change in concentration will be opposite, right? Like suppose if volume becomes half, rate of the reaction becomes double. So volume becomes half, concentration becomes double. So when concentration becomes double, right? Then rate of the reaction we can think of here. So before going into the relation of rate and concentration, let us try and understand one relation here first, right? Because I can say, I can say this, concentrate, don't write this, okay? Concentration is directly proportional to the rate of the reaction, but it is not true for all types of reaction, for all order of reaction. We have few reactions in which the rate is independent of concentration. We have few reactions in which the rate depends upon the square of the concentration, directly proportional to the square of the concentration. So before that drawing the relation of rate and concentration, we have to first understand the order of the reaction. So rate and concentration relation depends upon the order of the reaction, okay? So write down in this first, rate of reaction, rate of reaction is found to be, is found to be dependent, dependent on concentration of reactant, concentration of reactant in complicated manner, in complicated manner. This dependency, this dependency also changes with, changes with the progress of reaction, progress of reaction. What is this last line means? I'll come back to this point later on, okay? Dependency also changes with the progress of reaction, okay? So for any reaction what we can write, for any reaction, rate is directly proportional to the concentration of reactant to the power n, where n is the order of the reaction, n is the order of the reaction, okay? Now in this we have a relation, did you finish earlier? So to understand this particular relation, we'll have a law and this we have also discussed in chemical equilibrium, that is law of mass action. So according to this, what we can write, suppose we have a reaction, a statement I'm not giving you, it's not important. Suppose we have a reaction A A plus B B and this gives product. So what it says the law of mass action, the rate of any reaction is directly proportional to the active mass of, the active mass of the reactant to the power, we'll have some number over here, any number we have here, okay? This A and B, you can take it as concentration for calculation for question solving, but actually the term here you should use is active mass, active mass of A and active mass of B, okay? Active mass if you see the definition, it is different from concentration, it is there in graduation things if it is there. In 12th grade active mass is not given in most of the books, but active mass like I said for solving questions, you can consider this as the concentration because the value that be given in the question, it is given active mass only, but it is written concentration. Active mass is what like I said, suppose you have a reactant, so on the reactant we have, this is the volume of this, on this surface there are few areas which are active, activated area of this, these areas are active in nature and most of the areas are dormant, right? They are not prone to the reaction. So when the collision takes place within the reactant molecule, if the collision happens between the active surface area of the two reactant molecule, then there are chances of forming product, this is one of the criteria. See, we discussed this thing later on also in this chapter, when the collision happens within the two reactant molecule, this collision may be effective or non-effective collision, both type is possible. Effective collisions don't write this, we'll discuss this later also I'm just giving you an idea. Effective collisions are those which gives you the product, non-effective in which the product does not form, right? So effective collision, the collision should be in a proper manner, the orientation of molecule should be proper, orientation in the sense when the two molecules collides their active surface area must be in contact, then the collision is said to be effective provided if other conditions are there, other conditions we are not discussing it now, okay? So active mass corresponds to these active surface area only, correct? So the question that is given in your textbook, it is written concentration, but they have considered as the active mass only. So for definition we say rate according to this law, the rate is directly proportional to the active masses of reactant to the power, we'll have some number over here, this number could be anything, what is that and I'll come to that once again. So when you write down the definition of law of mass action, the statement, you don't write the concentration term, use active mass word over there, okay? Now this X for A, this could be equals to A and Y could be equals to B, it is possible, X, it is also possible, it is not equal to A and Y it is not equals to B, any possibility here, both possibilities, this is possible, this is possible when the reaction is complex reaction, you know what is complex reaction? Complex reaction means multi-step reaction, multi-step reaction, this is possible when the reaction is what? Reaction is simple reaction, simple reaction means what? Single step. Single step, which happens in one single step, right? So initially, law of mass action was given this, initially what was there, you don't write this, I'm just writing it down to make you understand and then I will correct it, initially the first statement which is given for law of mass action, they said what? The active mass of A and B to the power which is equals to the asymmetry coefficient of the respective, you know, reactivity, but this relation was found to be wrong for most of the reactions, it was found to be wrong for the reactions like complex reaction, then we modify it, okay, and we get a new rate law, in new rate law what they said that the power of this active mass could be any number, X and Y, and this X and Y, depending upon the nature of reaction, may be equals to the asymmetry coefficient or not equals to the asymmetry coefficient, did you get this? Yes? Right, so if you remove this proportionality sign, what we get, R is equals to a constant K, concentration of A to the power X, concentration of B to the power Y, where this K is the rate constant, okay? K is the rate constant, simple reaction, we also call it as elementary reaction, okay? Terms you must remember, simple reactions are elementary reactions, complex reactions are non-elementary reactions, all our same things. So this is law of mass action we have, okay? Now what is order? Write down the definition of order. It is the sum of, it is the sum of the power of all concentration term, it is the sum of the power of all concentration term appearing in rate law expression, appearing in rate law expression, okay? So what is rate law expression, RLE, rate law expression is this, this one, which we get according to the law of mass action, okay? This is rate law expression, going forward we'll use RLE for rate law expression, okay? So order is the sum of the power of the concentration term present in rate law expression. So with this definition, N is the order equals to X plus, this is the order of the reaction, with respect to this I'm talking about. This order is the experimental quantity, it is the experimental quantity. We cannot say by looking at the reaction that the order of the reaction is this, that we cannot say, okay? Means the point I'm trying to make, if the reaction is written N2 plus 3H2, I don't know the order of this reaction, okay? And really I don't know. But if the reaction is this, then you cannot write the rate of the reaction is K N2 to the power one, and H2 to the power three, that you cannot say, because you do not know whether the, what is the order with respect to N2 or H2? If it is elementary also, okay? So this you cannot write it. If the rate law expression for any reaction is not given, you cannot find out the order of the reaction. Are you getting my point? It must be given in the question. Yevala reaction, it must be given in the question. If it is not given, you cannot find out the order of the reaction, okay? Because it is experimental quantity, you never know what should be the power of N2 over here, whether it is one, whether it is half, whether it is one, right? So order can be anything, okay? Write down this two, three points here. It is an experimental quantity. It can be negative, positive, zero, or any fractional value. Negative order generally rare over, right? It's not, if the order is negative, then the reaction is, you know, it's very complex reaction. So the question is negative order is possible or not? Yes, it is possible, but it is rare, okay? So order can be positive, negative, zero, or any fractional value, experimental quantity. By looking at the reaction, we can see that the order is very complex reaction. So the question is negative order is possible or not? Yes, it is possible, but it is rare, okay? We cannot write down this RLE, rate law expression, we cannot write down. If the question is what is the rate of this reaction, then you should ask, sir, what is the rate law expression? Without this, you cannot say the order of the reaction is this, okay? Keep that in mind, right? Understood? Okay. Sir, can you write this if it's an elementary reaction? See, the thing is, if it is elementary reaction, and you know this, then you can write. Okay, mostly it happens, but since it is an experimental quantity, so it may be different for few reactions. Like it is like one over here, but maybe it is possible that rate is not very linearly with N2. I'm just giving an insight of it because it is an experimental quantity. You cannot relate this with this stoichiometric question. There's no relation of this. It is true that most of the elementary reaction, this relation is found to be correct, right? But don't know if all it is possible or not, okay? Okay, sir. Right, so I'll come back to this order again. Let's discuss this key. How do we define rate constant first? So rate constant, write down, it is the rate constant. It is the rate of a reaction. It is the rate of a reaction. When concentration of all the, it is the rate of the reaction, when concentration of all the reactant, and concentration of all the reactant present in, concentration of all the reactant present in, rate law expression is taken as unity. taken as unity, okay? The rate constant, it is the rate of the reaction when concentration of all the reactant present in rate law expression is taken as unity. So it's very simple you see rate we can write down rate is equals to k times concentration of a to the power x concentration of b to the power y and obviously if you take concentration of a and equals to b equals to 1 then rate is nothing but the rate constant k. So this is why when this concentration becomes unity rate constant becomes the rate of the reaction, right? That's why this term rate constant we also call it as velocity constant another term like another name of the same term rate constant is also velocity constant and this is also known as a specific rate constant sorry specific reaction rate because it is at the specific concentration specific reaction rate or a specific rate of the reaction. So rate constant velocity constant specific reaction rate all are same thing, okay? Unit if you see the unit of rate we know it is mole per liter divided by time. This is a unit of rate we have unit of time could be anything it can be minute second or day year anything, right? Unit of time it is mole per liter the concentration, okay? So with respect to this if you find out the unit of rate constant k that would be equals to we can write rate divided by a to the power I'm just drawing all these things with respect to this reaction, right? So if I substitute all the units over here, so rate is mole per liter into one by time and this one is mole per liter to the power x plus y. What is x plus y? Order. So can we write this as the unit is mole per liter to the power 1 minus n time to the power minus 1? Yes. So this is very important the unit of k because sometimes in the question they won't mention the order of the reaction because they have given the value of k with their unit, okay? So once you know the unit you can find out the order of the reaction and then you can use the equations accordingly, right? So for different orders what is the unit of the rate constant k, okay? So this side you write down the order unit of k rate constant 0, 1, 2, 3. Most important is 0 and 1. Second order is also there but it is not that important, okay? 0 if you substitute so the unit will be mole per liter time inverse. This would be mole per liter 1 minus 1 is 0. So t is time inverse order is liter per mole time inverse and for third order it is liter per mole square time inverse. If you want to keep this in mind mole per liter then you can say mole per liter minus 1, mole per liter minus 2 that also is okay? So you see the unit of k is not constant. It depends upon the order of the reaction. So suppose the question is given with the value of k and its unit is given, then once you know the unit you can find out the corresponding order of the reaction, okay? That's why this is very important. Write down this rate constant, rate constant constant depends on temperature. This is the major factor we have temperature catalyst activation energy. Once they have asked this question also that the k value they have given then what is the order of the reaction? Simply like this, like for a particular, they have asked this question in J only, okay? For a particular reaction the value of rate constant k is equals to 3 into 10 to the power minus 3 liter to square mole minus 2 second inverse. What is the order of the reaction? Three order, right? Order for this reaction is 3. N value is 3 and that is the answer. So this was a very simple one, okay? But this is very informative, this particular unit, okay? So let's take care of that. Okay, one note you write down here. If order with respect to one reactant is negative, if the order with respect to one reactant is negative, it means the reactant, it means that particular reactant is acting like an inhibitor, is acting like an inhibitor and the mechanism of reaction is quite complex. So could you repeat that? Yeah, if order with respect to one reactant is negative, with respect to one reactant is negative, then the reactant is behaving like an inhibitor, behaving like an inhibitor and the reaction is quite complex, is quite complex. So one example in this you see, the reaction is 2 O 3 gives 3 O 2 and the rate law for this expression for this reaction is r is equals to the rate constant k, concentration of O 3 to the power 2, concentration of O 2 to the power minus 1, okay? Now there is one thing here, like I have seen this in many 12 standard book that, no, you will see this kind of questions also, that this kind of rate law is given, what is the overall order? So overall order, if they ask you, that would be So why the O 2 coming? Isn't it only like reactant? This reaction we'll see later on, it's not a single step reaction, it's a multi step reaction, okay? How this O 2 is coming over here, we'll discuss this in the mechanism of reaction, the second part of this chapter, okay? I've just given you an example, okay? Let's not, you know, go into this detail of this, okay? One thing just you have to keep in mind, in rate law expression, we never have any intermediate in this, right? You can have reactant or product, but no intermediate in this, just as suppose A 2 converts, converts in A dot and A dot then with B 2 it converts into A B, okay? And then again B dot with B dot will get B 2, suppose the reaction is one second, A B plus B dot, I'll write down like this rate. Suppose the reaction is this A 2 plus B 2 and this is converting into 2 AB, right? But from this reactant to get this product, we have many intermediates in between, right? That intermediate could be what this A 2 converts into 2 A, right? B 2 converts into 2 B and then this A 2 A plus 2 B combines, converts into 2 AB, right? So reactant is this, this product is this. These are intermediates we have here. So when you write down the rate law expression, the rate in the rate law expression we can always have either reactant or product, intermediate should not be there, right? So how to write down the rate law expression if you have certain information that we'll discuss later, right? Not now, the second part of this chapter we'll see that. So when you discuss that you will understand that what are the steps in this conversion we have and with that is steps how to write down the rate law and then you will see O 2 to the power 1 negative minus 1 is there. That's why we are having it here, okay? So it will discuss this later. I'm discussing something else over here. What I'm discussing is the overall order of this reaction is generally we add this x plus y. So here we can also add 2 plus minus 1 is equals to 1. This is given in 12 standard book. Like if they ask you the order of the reaction they'll do like this. But some higher standard book if you study they say what? That if the order with respect to one species is negative then the reaction is quite complex and we cannot add the order of the individual species like this in order to get the overall order of the reaction, right? Means we cannot find out the order in this case. But I have seen what? I have seen in 12 standard book that they have taken answers like this, okay? So maybe you know since they have asked what is the overall order we don't have any choice, okay? We have to do like this only. But just one thing like I said that the mechanism becomes quite complex and in that case the order is difficult to determine, okay? But if they ask you you have to write down this the answer for this question. Suppose if they ask you what is the inhibitor in this answer would be O2 because with respect to O2 the order is minus 1. With respect to O3 the order is 2. Are you getting it? So when you write down this expression rate R is equals to, sorry, rate R is equals to K concentration of A to the power X concentration of B to the power Y means X is the order of reaction with respect to A and Y is the order of reaction with respect to B, okay? Sometimes they'll ask this kind of very simple question. Suppose a reaction is given that is 2A plus B and this gives product here. Order with respect to A to A is 2. Order with respect to B is minus 1, right? With respect to B is minus 1. Then first question what is the rate law expression RLE? What is the overall order? Tell me quickly. What is the rate law expression? LE since we know the individual rate with respect to the species RLE is equals to, will have rate is equals to constant K concentration of A to the power 2 and concentration of B to the power minus 1. A to the power 2, B to the power minus 1. What is the overall order? Overall order, right? Since it has been asked, we don't have any choice. We have to add the 2 as 2 plus minus 1 is equals to 1. Now the third question in this, C, you do this one. Effect on rate, effect on rate if concentration of A is doubled. Effect on B, sorry, effect on rate if concentration of B is reduced to one-third, okay? So how do we do this? Yes, the answer is correct. You can do it in single line only. R dash is equals to the constant K, concentration of A becomes 2A, 2 and B as it is minus 1. So R dash is equals to 4R, concentration becomes 4 times, okay? A reduced to one-third. So again, R dash equals to K, A as it is and B is 1 by 3B minus 1 and hence R dash equals to 3R. Sometimes in the question, they'll change both the reaction. Like if I take A becomes double and B becomes one-third, then the new rate would be what? If you compare A double and B becomes one-third, then new rate will be 12 times, right? So both they can also change, okay? Based on this rate law expression, you can do this easily, not a big deal, right? Now one more thing, you see the fifth one in this. Sorry? Sir, is those other parts a question or something? Same question, the sub parts in this we have, 1, 2, AB we have done, then BCD and this one is E. Same question. Effect on rate, if volume of container is doubled, okay? So volume of container is doubled means what? Concentration becomes half, right? So A dash equals to, we can write A by 2 and B dash is B by 2. So if you substitute rate equals to K concentration of A by 2 square, concentration of B by 2 minus 1, right? This would be R dash. So this is R by 2. This is the answer here. R dash becomes R by 2. One thing I'm going to generalize here, okay? Directly you can use this formula in the exam. New rate is this, right? So we can write the new rate or simply rate you can write is directly proportional to 1 divided by the change in volume. Means volume becomes, of the container is double, right? So the volume is twice. So the factor of volume we can say, of volume to the power n, that is the order of the reaction. If it is second order reaction, you'll be getting here 2 square. Third order, 2 to the power cube. When it is simpler, you won't have any difference. You can do that easily. But for second and third order, there will be a bit of calculation. So in order to avoid that calculation and save your time, you can directly use this formula. New rate is equals directly proportional to 1 by factor of volume. It is doubled, right? Volume of container is doubled. So 2 to the power the order of the reaction. Clear? No doubt. This question you see. A gives P. Information given is the rate becomes half when concentration of A, rate becomes half when concentration of A increases by 4 times. Determine order with respect to A. Yes, minus half. So how do we do it? Just one question. We are doing it simple only so that all kind of questions you'll see. R is equals to A. Order we do not know. So A to the power n. New rate is R by 2 is equals to K. And this is 4 to the power n A to the power n. You can take the ratio of it, right? So when you take the ratio, it becomes 2 is equals to 1 by 4 to the power n. And hence n becomes minus half. So order with respect to A is minus half. Copy this. A plus B gives product. The data that is given, A becomes double. Rate becomes 4 times. And obviously when we are changing A, B is constant. And when we are changing B, rate becomes 1 by 3 times. Find the rate law expression. What is RLE? A square B minus 1. Yeah. So overall order is 1 you are getting, right? Yeah. So how do we do this? I'll assume rate R is equals to K A to the power A and B to the power B. So A double rate becomes 4 times. So it is 4R for the first set of data. K 2 to the power A, A to the power A and B to the power B. For the second set of data, it is 1 by 3R, K A to the power A and 3 to the power B. So this 2, we can take the ratio. 1 by 4 is equals to 1 by 2A. So A equals to 2. And this 2, if you take the ratio, 3 is equals to 1 by 3 to the power B. B equals to minus 1. So rate law expression is R equals to K concentration of A to the power 2. B to the power minus 1. Overall order is 1. On the same type, you can have 3 reactant also. So one question on this also, we'll see. A plus B plus C is product. On doubling the volume, volume of container rate decreases by 8 times. If A doubles and B reduces to half, rate becomes 4 times. If C concentration of C increases by 4 times, rate increases by 64 times. Determine order with respect to A, B, and C. Write rate law expression. All of you are getting 1 minus 1 and 3. R is equals to K A to the power P, B to the power Q, C to the power small R we have here. On doubling the volume of container, the rate decreases by 8 times. So we'll have R by 8. Volume doubles, concentration becomes half. So it is, what if I take simply this one is. If you take the ratio, then this becomes 1 by 8 and this becomes 1 by 2 to the power. P plus Q plus R. After taking the ratio, you'll get this first data. If A doubles, B reduces to half. If A doubles, B reduces to half. The rate becomes 4 times. So we'll write here, this is 1. A doubles 2 to the power P, B reduces to half, 1 by 2 to the power Q is equals to, we have 4 divided by 1. That is 4 only. It is 2. And thus C increases by 4 times. Okay. So C is 4 times the 4 to the power R is equals to 64. That is 3. So R is 3 here. And P plus Q from this will get P plus Q as 2. R is 3. P plus Q as 2. And P plus Q plus R. So P minus Q is 2. Okay. That's what I was thinking. Why it is P minus Q is 2. P minus Q is 2. And P plus Q plus R is 3. So R is 3 and 3 will get cancelled. So it is 0 this side. P is equals to minus Q, minus Q is equals to P. So 2 P is equals to 1. I'm getting minus 1. Yeah. Q is minus 1. 1 minus 1, minus 3. So it's correct. Okay. So this is this type of questions you get here. Okay. Thus you need to assume the other reactants which is not mentioned constantly. Now for various reactions, there are rate law expression. So for some reaction is important for you to memorize the rate law expression. Okay. So examples you write down examples of rate law expression of RLE. The first one, the reaction is 2 and 205 gives 4 and 2 plus O2. Rate of this reaction is rate law expression is K and 205 to the power 1. This is very important. Okay. This one is the first order reaction. Okay. It does not look like, but it is a first order reaction. Second one, we have 5 Br minus plus BrO3 minus 6 H plus converts into 3 Br2 plus 3 H2. This reaction we have. And the rate law expression for this one is R, K times Br minus minus 1 BrO3 minus to the power minus 1 and H plus to the power 1. That is plus 1. Okay. For ozone, I have already given you the reaction 32O3 converts into 302. And the rate law expression for this is K O3 square O2 to the power minus 1. Okay. So this one is also important here. Done. So one thing you see here, in this example, this is the reactant present in the rate law expression. This is the product present in the rate law expression. Can I go to the next page? Okay. The fourth one is NO2 plus CO NO plus CO2. And the rate law expression for this reaction is K times NO2 square. And we have CO. It is actually independent of CO. So CO to the power 0. The order with respect to this is 0 here. So it's not like all the reactant must present in the rate law expression. Acetyldehyde CH3CHO, where it converts into CH4 and carbon monoxide. Its rate expression is RK times of CH3CHO to the power 3 by 2 fraction. And the last one, this one is also important. The reaction is SO2 plus O2. This reaction takes place in presence of NO catalyst. NO catalyst, the product is 2SO3. And the rate law expression for this one is K concentration of O2 to the power 1 and concentration of NO to the power 2. Right? So you see this, NO is the catalyst here. So it means along with reactant and product, catalyst may also present in the rate law expression. Sir, so when we say it's like a good catalyst, that means it'll have a higher order for that catalyst. No, both are different actually. Order is something else. Good catalyst, I think you're talking in terms of whether it increases the rate of reaction or decreases. Right? Yes. So the term that we use is positive or negative catalyst. With respect to order, we can say how it affects the rate of the reaction. Right? So if order is more, right, rate of the reaction is more, we can say it is positive catalyst. If it is positive catalyst, right? See, we cannot generalize like this because it's not like all the catalysts in all reactions must present in rate law expression. Yes, for those reactions in which the catalyst is present, we can say that catalyst is a positive catalyst or a good catalyst. Right? So whatever you said is true for the reaction in which the catalyst is present in rate law expression. Okay? Got it? So based on all these examples, few characteristics of RLE, you must remember, theoretical questions, they frame on this. Write down one by one. In RLE, we can have product or catalyst or catalyst along with reactant. There is no relation between the stoichiometry order of reaction. Right? I've already discussed it. The reaction intermediate intermediate will never appear in RLE, rate law expression. Last point, only for simple or elementary reaction, simple or elementary reaction or elementary reaction, the order of reaction reaction is equals to the stoichiometric coefficient of the reactant. Next point, all these theoretical information that we have on this also you will have questions. Okay? Order of the reaction of the reaction also changes with the condition in which the condition in which in which the reaction is taking place, taking place. For example, you see, for this particular point, you see the composition of gases at solid surface, gases at solid surface follows first order reaction, follows first order. This, on this question we have asked, follows first order at low pressure. Means when the pressure is low, it is first order. Right? The composition of gases follows first order at low pressure. At high pressure, high pressure, the order is zero. The order is, right? So condition is also important here. Three examples are very important here. The reaction is H2 plus Cl2 gives 2 at Cl and this reaction is a complex reaction. Complex reaction of zero order. The rate law expression is K, H2 to the power zero, Cl2 to the power zero. If you take H2 plus Br2, this three you must remember. Okay? H2 plus Br2 gives 2 HBr. This is also a complex reaction and its rate law expression R is equals to K1 H2 to the power one, Br2 to the power half divided by 1 plus K2 HBr divided by Br2. This is the expression, complex reaction. And the last one we have, that is H2 plus I2. H2 plus I2 forms 2 HI and this is the simple reaction or elementary reaction. So its rate of the reaction is K times H2 to the power one, I2 to the power one. This is the rate law expression here. Okay? Okay. Well, last question in this, the last type we'll see here and then we'll start with the kinetics of various order of reaction. The question is N2O5, so first order reaction gives 4 NO2, 4 NO2, yeah, 4 NO2 plus O2. The rate of disappearance of N2O5, that is dN2O5, rate of disappearance of dN2O5, that is minus of dN2O5 by dt is equals to K1 times N2O5 to the power one. It is given. It is the rate constant with respect to N2O5. K1 is the rate constant with respect to N2O5. Appearance of NO2 is equals to K2 of N2O5. Okay? K for N2O5, K2 for NO2 here and d by dt of O2. Appearance of O2, it is K3 of again N2O5, rate constant with respect to O2. We need to derive a relation among K1, K2 and K3. Try this. K1, K2 and K3. Drive the relation among these three. Yeah, that's right. So, we can simply write this, the rate of the reaction ROR is equals to R is equals to 1 by 2 minus of d N2O5 by dt is equals to 1 by 4 plus of d NO2 by dt, 1 by 1 plus of d O2 by dt. Okay? So, all these expression will express in terms of K1 in this. So, R we can write as rate constant of the reaction, reaction rate constant into N2O5 to the power 1 because we know it is a first order reaction equals to half of K1 N2O5 to the power 1, 1 by 4 of K2 N2O5 to the power 1, 1 by K3 N2O5 to the power 1. So, we can write what? We can write K is equals to, K is equals to K1 by 2, K2 by 4 is equals to K3 by 1, where this K is the reaction. So, just a second. Yeah, so for this question, the relation is this, where K is the reaction rate constant. So, in general, what we can write here is, suppose we have a reaction A A plus B B gives C C plus D D. So, the reaction rate constant K is equals to K A by A is equals to K B by B, K C by C, K D by D. This is the relation we can write, where K is the reaction rate constant and these K A, K B, K C, K D are the rate constant for individual species. This K is the done. So, next we are going to start kinetics of various order reaction. Okay. We'll start this after the break. Okay. Zero order, first order, second order and then all these things we have to see here. What is the equation, examples and all? Correct. Take a break now. We'll resume at 6.30.