 Okay, so the great topic that we are going to start is chemical kinetics. See actually As far as this board exam or this J exam is concerned. Okay, so chemical kinetics is a very Interesting topic like important topic interesting and as well as scoring old. Okay, like it is not like normal Chemistry topic that we have where we have to know memorize most of the things, right? Or like you have to certain things you have to memorize and then you have to apply some concepts. Okay, so This chapter is more about it is I would say it is mathematical, right? You have to use the concept of integration and then little bit of derivation is there based on that We'll get some formula. Okay, and on the basis of formula will solve some questions. Okay so basically this chapter there are very few things you have to keep in mind comparatively and Most of the things are logical that you can understand easily and solve, right? Okay, so now before Starting this chapter Let me give you a little bit of you know in Instruction or introduction about chemical reactions because it is chemical kinetics We are going to discuss so in chemical kinetics. We are again going to discuss about chemical reaction. Okay, and With respect to chemical reaction, if you see we have already done like, you know many Already done two chapters in the previous class like 11th class okay, and What are those chapter those chapter are Thermodynamics and chemical equilibrium. Okay, let me tell you if you have any doubt in this you can text me Right in the comment box. You can write I will give you the response on that. Okay, any doubt you can ask me Okay, don't simply Look at and go through whatever we are doing here in the class, right? So any doubt you can text me in the comment box. Okay coming back to this we have done two chapter basically in the 11th class that is thermodynamics thermodynamics and chemical equilibrium chemical equilibrium You see in thermodynamics what information we get we get the information about feasibility of reaction, okay in thermodynamics We get the information about feasibility of reaction feasibility means what like under a given set of condition whether a given reaction is possible or not or not Okay, and for that the sufficient condition is what the change in Gibbs free energy should be less than zero Correct. This is the condition we have discussed. Okay, so basically from this chapter we can easily understand that So basically in this chapter we can easily understand in thermodynamics that whether a given reaction is possible or not under a given set of Foundation chemical equilibrium if you remember we mainly discuss about a reversible reaction Right reversible reaction we discuss over here and we also discuss about direction of the reaction like under a given Set of condition the reaction proceeds whether in forward direction or Backward direction that is what the direction of the reaction. So basically These two times chapter if you discuss if you see we have understood two aspect of a chemical reaction and that is whether the chemical reaction is possible or not or Under a given set of condition with the reaction will go into forward direction or backward directions, okay? So this is the two things we have discussed now suppose if I write down one reaction here and that reaction is C plus O2 Gibbs C O2 Or suppose if I write one more reaction and 2 plus 3 H 2 Gibbs 2 NH 3 Right if I ask you whether this reaction is possible or not you will use the concept of thermodynamics and you can say What direction the reaction proceeds? Okay? Use a concept of chemical equilibrium. You can say right, but if I ask you like What is the rate of the reaction? rate of the reaction or if I ask you after what time after what time The reaction get Over gets over Okay, after what time the reaction gets over correct these two question if I ask you So obviously you cannot answer these two questions now because still now we haven't discussed about the rate of the reaction and again After what time the reaction gets over, okay, and rate of the reaction means what the speed at which the reaction is proceeding the reaction is proceeding Okay, this thing we haven't discussed in now, okay Now in this chapter, we are going to discuss about mainly about the rate of the reaction Okay, how do we find out rate and? After what time the reaction gets over, okay Now you see this chapter in this chapter, we are going to discuss about three things We are going to discuss that is rate of the reaction first Okay, then We'll discuss about factors affecting factors affecting the rate of reaction Rate of reaction in short will write ROR. Okay. We'll use this notation ROR factors affecting the rate of reaction and in the last we also discussed about mechanism of reaction Mechanism of reaction mechanism of reaction if you try to recall We have done organic chemistry already and there we discussed the mechanism of reaction And if you remember there, we also discussed which is RDS rate and determining a step, okay So the information of this RDS rate and determining a step, which is the slowest step if you remember, okay slowest step so whether and slowest step means what the reaction is going with the slowest speed Like the speed is slow of the reaction. So this information of RDS rate and determining a step We get from the concept of chemical kinetics only. How do we understand this? That which step is the slowest step already determining a step that also will discuss in this chapter But that we'll discuss in the last. Okay, first we'll see the rate of the reaction and factors affecting the rate of the reaction And then we'll see in the last mechanism of the reaction. Okay So now you write down just the introduction of this if you are there just I'll dictate you you'll write down Chemical kinetics or I'll also write down here chemical kinetics chemical kinetics is the branch of Physical chemistry is a branch of physical chemistry which deals with which Deals with the rate the rate of the reaction rate of the reaction and Factors affecting affecting the rate of reaction It also deals with deals with the Mechanism of reaction mechanism of reaction Okay, so this is the this is the Introduction of this chapter we have done. Okay. I hope you all have written so that I can drop this Okay, okay Now you see next Okay, now the first thing that we have here is The rate of reaction Okay, what is rate? Right, it is anything change in quantity with respect to time. That is what the rate we have Okay, like we discussed The rate of change of displacement is nothing but velocity right rate of change of distance is nothing but speed So when we say rate of change of distance what we write distance traveled per unit time Okay, or displacement per unit time. That is what the rate of change of displacement. So whenever we talk about rate we always Try to understand the quantity change in quantity with respect to time Okay, so rate if I try to explain or if I try to write down here rate is what it is the change in Any quantity any quantity with respect to time. This is what the rate we have Okay Now if I talk about the rate of reaction okay the rate of reaction Since we have reactions reaction in the reaction either we deal with Concentration or if the reactant and product are in gaseous state then we deal with pressure Okay, so since concentration and pressure we are dealing with in the reaction The rate of reaction will what we'll write will write change in change in Concentration of reactant or product change in concentration of reactant and product Divided by the time taken for this change Okay, change in concentration of reactant and product divided by the time taken for this change And that we can also write del C divided by del T okay change in concentration Divided by the time taken for this change Okay, now if the reaction is in gaseous phase Okay, if the reaction is in gaseous phase, so instead of concentration will write the change in pressure right, so we'll write what change in pressure of reactant are for reactant or product Divided by the time taken for this change and that also we can write del P by del T Okay, and this relation is true for gaseous reactant gaseous Reaction simply arrived okay reactant or product Okay, so this and we know like you know This pressure and concentration is directly proportional also P is equals to CRT We write from PV is equals to NRT from PV is equals to NRT. We write P is equals to CRT So whenever you multiply RT with concentration, you will get pressure and whenever you divide Pressure with RT you will get concentration. So these two we can easily entertain interchange right pressure and concentration term, right? Okay, now when we are talking about the rate of the reaction see we have already discussed The various types of classification first of all, let me tell you there are two types of rate we have which must you which we must have done already in the You know of physics and that is instantaneous result average rate Okay, so two types of rate we have that we'll see right now. Okay, so I'll rub this off now rate of reaction are of two types two types of ROR rate of reaction Okay, the first one we have instantaneous rate and the second one we have Average rate, okay the first one we have Instantaneous rate of reaction and the second one we have average rate of reaction Okay, instantaneous rate means what it is a rate at a particular time Okay, it is a rate of change of concentration or reactant or Product over a very small time interval. Okay, if I write down the definition of this it is the rate of change of concentration of reactant or product concentration of reactant or product over over a very small time interval time interval Average rate is what change in concentration and reactant Over a large time interval basically, okay over a particular Direction of time. Okay, so basically del T is large over here. Okay, so here we have a very small time interval Here we are comparatively large time interval into this. Okay, now you see one graph into this the concentration and time graph if I draw This is the concentration axis and this is the time concentration and time graph if we draw the graph is will get something Like this the nature of graph Okay, you can ask me why the graph is like this, right? Because we have like if I draw a straight line then the graph must follow the same pattern What about the okay? Atmish had some doubts or what about the case where the product and reactant on different phase and As in one of the gas phase see whenever we have different phase see what I said atmish See whenever we have different phase liquid and gas suppose we have okay, so You since we have the constant the rate is what the change in concentration per unit time Right or change in pressure per unit time So basically whenever we write down the rate of the reaction we can write down in terms of product also or in terms of reactant also Both we can write that we'll see later on in this chapter today only we'll see that so rate of any reaction We can write down in terms of product also or in terms of reactant also That's why we see wherever we have written the rate of reaction. Okay, so rate of reaction What we have written rate of change of concentration of reactant or product Okay, so base Basic thing is what we can write down the rate of any reaction with respect to concentration also and with respect to product also right and in both case will get the expression of rate of the reaction when the product is in gaseous phase Preferably will take pressure over there and when the product even the reactant is in liquid phase Preferably will take concentration into that. Okay, you'll get the same answer into that Okay Yeah, like there is also right you can any time you can convert, you know Pressure and concentration because the reaction always takes place At a constant temperature or pressure. Okay, so that must be given. Okay, so I hope you understand this Yeah, okay, okay, so now you see like we were talking about the graph of this Okay, concentration and time time see everything in this chapter. Okay, let me tell you one thing. Okay, whatever I'm telling you It's every single word you have to Understand very clearly. Okay, this chapter looks like Very easy. Okay, but there are some concept. Okay. I'll give you some questions Okay, you'll you'll understand what minute minute things you have to keep in mind over here Okay, like you see here Concentration and time graph I've given you like this Okay, why I've drawn like this. It can be anything. No, we don't have any, you know Relation of concentration and time time till now, right? If we have this relation y is equals to mx plus C then we are sure okay It will be a straight line and we can draw a straight line according to the reaction here, right? According to the equation we have here, but since I have given you this thing directly, right? But we do not have till now the relation of concentration and time Then why I've given you this graph. Okay, this this is one of the question that you may have you might have, right? But the thing is right now You just let it be don't think about this that why the graph is like this, you know one thing I'll tell you the concentration and Time graph that you have. Okay. It is a very complex relation the concentration and time Okay, it depends on the order of a particular reaction I remember some of you are asking me about what is the order of reaction when I was discussing about that base catalyzed base catalyzed Asylation, okay, but BAC2 type reaction and BA P1 type reaction there when I said order is two order is one Some of you have asked me so what is the order of the reaction? What do you mean by the order of the reaction? And if you remember I told you that time that order will discuss in chemical kinetics Okay, so here we are discussing this so with respect to the concentration and time that you have This graph we can draw Depending on the order of the reaction Okay, this thing this term order will come to this later on. Okay So depending on the order of the reaction the concentration and time Relation will be different and according to that relation will have the graph of this Okay, so order we have to understand will come to this later on only one thing I'll just tell you right now. It is an experimental quantity It is an experimental value. Suppose if I write down n2 plus 3s2 gives 2ns3 and 2 plus 3h2 gives 2ns3 if I ask you what is the order of the reaction you cannot do anything into it Okay, you have to know this because order is what it is an experimental quantity with on the base of Experiment only we have given the order of the reaction all these things you are able to answer Once we finish at least 50% of this chapter Okay, so now coming back to this average and instantaneous rate that we have see the graph suppose Concentration in time graph suppose we have this now at time t is equals to t1 if I ask you what is the concentration? So so concentration will be what at time t is equals to t1 the concentration will be something like this was just c1 Right and after time t2 when the reaction proceeds and the reaction proceeds the time t2 the concentration decreases because like again you have to Ask one thing over here. You should ask one thing over here that what Concentration it is whether it is a concentration of reactant or concentration of product Okay, suppose if I write down one reaction a gives be correct Initial concentration of a suppose it is a not and it is 0 So when a starts converting into b So we see the concentration of a is decreasing with time and the concentration of b since it is a product It is increasing with time Okay, so this concentration is what concentration of reactant not product So we have taken here Concentration of reactant which is decreasing with time. You see the graph is going like this when the time is increasing Okay, so now here you see if I If I tell you the change in concentration over a period of time that is the average rate of reaction Okay, so change in concentration that is del c by del t Over a period of time. What will write final concentration minus initial concentration t2 minus c1 divided by the time required for this change is what t2 minus t1 This is the average rate of reaction. Is it clear? Is it clear any doubt? Let me know if you have any doubt. Okay, del c by del t is c2 minus c1 divided by t2 minus t1 Right, this is the change in concentration del c and this is the Time required for this change del t, right? So del c by del t is nothing but the average rate of reaction Okay, now if I talk about instantaneous rate of reaction which is over a very small time interval so that will write what will write del c By del t where this del t is what we can use the concept of limit over here del t tends to 0 Over a very small time interval. Okay, and this we write what it is a mathematical definition of derivative Okay differentiation dc by dt Is it clear let me know this relation is clear this mathematics I think you must have done all these things in calculus already. Okay, so del c by del t Limit del t tends to 0 is equals to dc by dt. Is it clear? Okay, so this is the mathematical definition of this Derivative, okay, so most of the time we are using this instantaneous rate of reaction only for our derivation purpose Because as I said we have to use Differentiation integration and all so we have to use this expression only for the derivation purpose Okay, so these are the two types of reaction we have