 okay see this chapter chemical kinetics it's completely mathematical okay you'll have a lot of integration to do okay shall we start you see this chapter is all about again we have chemical reactions only as far as chemical reaction is concerned yeah as far as chemical reaction is concerned we had already studied two different chapters okay and that is chemical reaction okay two chapters we have discussed in this and that is thermodynamics already we have studied in eleventh grade and we have also done that is chemical equilibrium what information we get from these two chapters you know for a chemical reaction as far as this chemical reaction is concerned what information we get from this two chapter thermodynamics and chemical equilibrium thermodynamics gives us the idea of feasibility of a reaction yes or no it tells us that under a given set of condition whether the reaction is possible or not and for that what is the condition yes tell me what is the condition feasibility of reaction under a condition we can talk about yes we can talk about spontaneity we can talk about delta g if delta g is less than zero we can say the reaction is feasible possible otherwise it is not possible non is spontaneous okay chemical equilibrium gives us the idea of direction of reaction right direction of reaction like under the condition in which direction the reaction proceeds right forward or backward right now suppose we have a reaction one simple reaction I'll write down that is carbon we have certain moles of carbon and we have certain moles of oxygen these two reacts and it gives a carbon dioxide okay so if I ask you suppose the number of moles of c and o2 is given and if I ask you by what time or how much time this reaction will take to finish for completion of this reaction right that is what time it requires for the completion of reaction that is what that is what the rate at which the reaction is proceeding right we did not talk about the rate of a reaction till now right you can see under under the given condition like okay it is it is feasible or not we can use a concept of thermodynamics and say you can also say whether it goes in forward direction backward direction based on all the data but if I ask you at what speed the reaction is proceeding right that is the rate of the reaction or by what time or after how much time the reaction will get over this idea we do not have since we did not talk about the rate of the reaction okay so this chapter actually you know deals with the rate of a chemical reaction how do we define the rate of a chemical reaction so this has two three different portions for this chapter three different sections you can say first it deals with the rate of the reaction it also deals with the mechanism of the reaction okay remember in organic chemistry we say what is the rate determining step what is the rate determining step so the slowest slowest step and how do you know which one is slowest step that idea you will have from this chapter once you know the rate of the reaction correct that's why we say that this chemical kinetics also deals with the mechanism of the reaction which step is the slowest step fastest step everything mechanism of the reaction okay and it also you know deals with the effect of various factors such as concentration pressure temperature catalyst on the reaction rate means reaction rate plus what are the factors which affect the rate of the reaction right and the mechanism of reaction got it all these things we are going to understand in this chapter we're also going to understand the order of the reaction like in SN2 SN1 we say you know who is the second order reaction first order reaction all those informations we'll have from this chapter understood okay so write down chemical kinetics deals with the rate of a chemical reaction i'll write down wait deals with the rate of chemical reaction it also deals with deals with the mechanism mechanism of reaction of reaction and and various factor various factors such as such as concentration oh i missed it effect of effect of various factor such as concentration temperature pressure pressure catalyst etc on the reaction rate on the reaction rate okay so this chapter actually no come you know completes the understand for you it's all finished or you know we can say this chapter gives you all the informations of the reaction rate and here the study of a chemical reaction the everything will get over when you finish this particular chapter okay we'll be understanding we have we have we have already done the feasibility they've all done the reaction direction and this deals with the rate of the reaction so everything of the chemical reaction will get over now since we are talking about the speed of the reaction so on the basis of the speed of the reaction the reactions are classified into three categories okay so write down on the basis of on the basis of speed of speed the reaction is classified any reaction is classified fired into three categories three categories the first one is very fast or we also call it as instantaneous reaction instantaneous reaction these are the reactions which gets over in like 10 to the power minus 14 to 10 to the power minus 16 seconds means as soon as the reactant comes in contact the reaction gets over right so these are the very fast reaction basically so all the neutralization reaction acid based reactions are the example of it okay examples of this reaction are neutralization reaction acid base reaction okay in acid base reaction what happens we have an exchange we're just ion exchange right any plus OH minus H plus Cl minus converts into NaCl plus water so it is the exchange of ion right ion exchange reaction and that's why this reaction we also call it as ionic reaction right so very fast reaction ionic reaction or instantaneous reaction all are the same thing precipitation reaction is also you know comes into this category like for example if you have Ag NaO3 reacts with NaCl then AgCl precipitates and will get Na NaO3 all these comes under the same category very fast or instantaneous reaction second type of reaction we have are you done okay second type of reaction we have very slow reaction just opposite rate very slow reaction means what corrosion it takes months right these are the very slow reaction extremely slow at room temperature right on very extremely slow at room temperature for example we have we have rusting of ion reaction of O2 H2 and O2 at room temperature gives H2O this is also a similar kind of reaction C plus O2 reaction of carbon and oxygen at room temperature formation of CO2 extremely slow reaction right why we are discussing all these things one type is extremely fast okay right you won't even get your time get the time to blink your eyes and the reaction will get over right that is the order of 10 to the power minus 14 and 10 to the power minus 16 and this one is extremely slow it takes months years to finish right that's why these two reactions we do not you know calculate or deals with in this chapter we don't calculate rate of these reactions because there is no point of calculating rate okay the reaction becomes is extremely slow or extremely fast so we don't deal with these two kind of reaction in this chapter we deals with what we deals with the reaction which has the moderate rate that is molecular reaction or we also call it as moderate reaction third type you write down moderate reaction we also call it as molecular reaction like the first one ions are involved here we have molecules are involved so molecular reactions proceeds with a moderate speed and we are going to deal with molecular reactions in this chapter mainly right on these type of reactions these type of reactions proceeds with this type of reactions proceeds with the moderate rate at room temperature moderate rate at room temperature many examples we have a reaction of n2 plus h2 n2 plus 3 h2 gives 2 NH3 is a moderate rate reaction okay dissociation of H2O2 to H2O plus O2 right growth of bacteria in the milk sample growth of bacteria in the milk sample all these are moderate reactions so in this chapter we are going to deal with uh moderate reactions so we're talking about rate of the reaction so first of all we'll see what is rate and how do we define the rate of reaction heading right down rate of reaction see if you look at the velocity how do we define velocity velocity is the rate of change of displacement or displacement per unit time is velocity distance per unit time is speed right point I'm trying to make is whenever this rate term comes it means we are we are dealing with per unit time right so rate means with respect to time we have to do the calculation right with respect to for a chemical reaction we deal with concentration right that's why for a chemical reaction the rate defines at the rate of change of concentration of either reactant or product per unit time are you getting it right so how do we define the rate of anything rate is the change in uh we can say the term or the change in quantity for example in general we define like this divided by the time taken to produce that change okay or the time required to produce that change this is how we define the rate okay right down in chemical reactions in chemical reactions the rate is defined as defined as the change in concentration reactant or product the rate is defined a change in concentration of reactant and product in a given time interval a given time interval okay now if I write down this the expression here of rate is equals to change in the concentration of reactant square bracket means concentration okay the concentration of reactant or the concentration of product divided by divided by the time required that is delta c concentration by delta t right when the reaction is given in gaseous phase or I'll write down here when the reaction is in gaseous phase then instead of this thing concentration will take what the pressure okay so rate in this case would be the change in pressure reactant or product divided by the time required to produce this change this is how we define the rate of a reaction then I am taking a simplest example here suppose the reaction is we have a and this is converting into a product so at time t is equals to zero we have certain concentration of a that is assuming as a and there's no product at this time so it is zero now since a is converting into b so at time t we have a minus x and this is x okay so rate is what rate with respect to a if we define that would be the change in concentration of a change in concentration of a concentration of a divided by the time required for this change this is equals to we'll write at time t is equals to zero the concentration was a at time t is equals to t the concentration becomes a minus x and this is divided by the time required is zero minus t it should be other way no t minus zero this is the time required for this change even the numerator in the numerator yeah that's right so here also we have a minus x minus a a minus x minus a okay this is a change in concentration now this becomes minus x by t correct so rate is coming out to be negative what do you mean by this as we go forward the reaction becomes lower that is not possible because if that is there then the reaction should not go in the forward direction this means it is a kind of you know in physics we say dissertation right those are like it will go forward but at a slower pace a is decreasing this means that a is decreasing yes a is decreasing but negative rate what do you mean by negative that's does it have any significance that the reaction is proceeding right a is converting into b with negative rate what do you mean by this sir i don't mean direction like change in or the concentration if it was using then as a direction see direction we can think about but here we i'm not assuming that because you know rate we can define for any reaction know whether it is reversible or irreversible i'm assuming what a is converting into any product so if you talk about direction then this thing won't be true for irreversible reaction okay but rate we can define for all kind of reaction whether it is reversible or irreversible see the thing is since a is converting into b so we must have you know rate positive here right negative rate does not have any significance you can think of you are going with sudden speed 10 meter per second and then again you're slowing it down that is a case of dissertation right there we can say that you know you are getting slower with time dissertation is there expression is there in the opposite direction but here the thing is not like that a is converting into b so here the negative rate does not mean anything so what we do here whenever we write this is the formula we have whenever we write the rate with respect to any reactant we'll consider a negative sign here that we have to introduce here also we have to introduce so that the rate becomes eventually positive so this is equals to negative of change of concentration of a because a is reacted divided by a time because the concentration of a is decreasing right to make it positive we'll just introduce a negative sign here right so this is what this is we are talking about two instant right the time when a is hey a has a concentration and the time when a has a minus x concentration if you plot a graph over here if you plot a graph over here of concentration and time this is the concentration axis and this is the time axis so graph is suppose it goes like this okay so at time whichever this will touch y axis my bad because at time t we have certain concentration of a right so this is the concentration of a suppose we have this is the concentration initial concentration of a time t is equals to zero as the reaction starts the concentration the concentration of a starts decreasing and hence this is the graph we have the concentration of a decreases and at time t at time t the concentration becomes this this is the concentration at time t this is the concentration is c not initially Okay, so this you know difference here you see once again, so this difference you see from this point to this point. This is the difference in concentration in a given time period delta C. And this is the time required for this change that is delta T. So this change is what this is the average rate of the reaction because over a given a period time right delta T time what is the change we have. So this rate we call it as average rate and if I write down the formula for this this would be one sec this would be delta C divided by delta T right. Now if what happens if this delta T almost tends to zero if you apply the limit over here I'll go to the next page a second I'll come back our average we have and when we apply the limit over here limit delta T tends to zero dC by d delta C by delta T. And what do you mean by this term instantaneously instantaneous right so this is the mathematical derivation sorry definition of dy by dx or dC by dt in this case right so this average when the delta T becomes zero this becomes our instantaneous instantaneous rate is dC change in concentration by T right. So you must have done all these things in physics also in the first chapter only the mechanics I know they have defined this average speed and instantaneous speed right all these things you have done already. So this is the average speed over a period of time when this delta T becomes zero so this point you see and this point it is almost you know next to it very close right and when you draw a line to join these two point that line will be the will be the what will be the tangent of this curve right at this point and slope of the tangent is dy by dx here it is C and T so dC by dt that definition you already have right so our instantaneous is dC by dt and our average defines over a period of time that is delta C by delta T mostly will use instantaneous rate for the calculation understood instantaneous rate for the calculation. So you see here once again right our instantaneous is our average is this okay so we had this equation A gives zero at sorry A gives a product P at time T is equals to zero it is I am assuming the concentration as A this is zero at time T is equals to T it was A minus X A minus X and this is X okay so our rate is our average if I write down that would be delta concentration of A by delta T with negative sign okay is equals to dC by dt with also negative sign instantaneous average so this should not write equals to but we can define both way this dC by dt is nothing but our instantaneous if I write down with respect to the product P here again this you know reaction we can write our average equals to plus of delta of concentration of P by delta T if it is our instantaneous it is minus just a second yes so this is the instantaneous and average beer what I have done I have done this product we have no sweat is plus sign okay for product it is always positive will write down here if I write down the rate with respect to product or rate with respect to reactant will consider the negative sign both are the rate of the reaction okay so overall the rate of this reaction we can write rate equals to minus of delta A sorry minus of delta concentration of A by delta T is equals to plus of delta concentration of product P by delta T average instantaneous if you write that would be minus of D concentration of A by dt and plus of D concentration of P by dt got it so product will write positive sign it's relative so reactant it is negative so product is positive rate of reaction write down rate of reaction one second write down rate of reaction we always define for one more means whatever the coefficient the expression of rate of constant rate of reaction is always with respect to one mole of reactant or product look at this example here suppose we have a reaction to a gifts 3b okay so at time T is equals to 0 suppose its concentration is a and this is 0 and at any time T it becomes a minus 2x and what is this 3x so if I write down the rate of a is the reactant it is not the rate of reaction it is the rate of a the reactant rate of a or rate of reactant or we can also write on the rate of consumption rate of consumption or rate of disappearance all these things are same okay consumption disappearance all these things are same is equals to we'll write minus of D concentration of a by dt okay this expression would be D by dt of change in concentration of a is a minus 2x minus x divided by t minus a right not x minus a divided by t and this would be what 2 times dx by dt similarly copy this down first I'll go to the next page rate of B rate of B B is the product so production rate of appearance anything we can write this equals to plus of D by dt of concentration of B which becomes plus of D by dt concentration of B is 3x minus 0 so this would be plus 3 dx by dt this dx by dt is the rate of the reaction this is the rate of the reaction per mode 3dx by dt is the rate of appearance of B it is the rate of reaction and we'll use this ROR abbreviation for rate of reaction okay ROR dx by dt is the rate of reaction you see the rate of reaction and rate of appearance of B is thrice of the rate of reaction if you go back here the rate of reaction is this ROR and rate of appearance sorry disappearance of a or consumption of a is twice to that of the rate of the reaction so if I find out dx by dt from this what is dx by dt is equals to you see here dx by dt is equals to this 2 expression you see I am considering this one the rate of the reaction rate of the reaction and this this 2 I am considering so dx by dt from this is 1 by 2 of minus D concentration of a by dt so 1 by 2 you can also write minus 1 by 2 dA by dt but I have written it this way because minus d by dA by dt is the rate of appearance of a that is minus dA by dt okay similarly if you write down the rate of disappearance this rate of appearance of this is dx by dt and this dx by dt if you equate with this this would be 1 by 3 plus of D concentration of B by dt so plus dB by dt is the rate of appearance of this and minus dA by dt is the rate of disappearance of a when you equate the two you will get the expression for the rate of the reaction and that would be dx by dt is equals to 1 by 2 negative of D concentration of A by dt is equals to 1 by 3 positive of D concentration of B by dt okay so this is the rate of you know reaction we have dx by dt is the rate of the reaction two notes you write down here write down rate of any reactant or product rate of any reactant or product is independent of its rate of any reactant or product is independent of its stoichiometric coefficient rate of any particular species or any reactant or product is independent of its stoichiometric coefficient second point rate of reaction rate of reaction can be find can be find out only when the chemical reaction is given only when right on balanced chemical reaction is given it of reaction can be find out only when the balanced chemical reaction is given since it depends upon the stoichiometric coefficient since it depends upon stoichiometric coefficient so keep that in mind for any individual species for any reactant or product rate can be defined easily you just need the concentration or pressure at two different points okay if the reaction is not given fine you can find out the rate of individual species that is of any reactant or product but if you need to find out the rate of reaction which is this dx by dt rate of reaction then you must know what is the balanced reaction what is the stoichiometric coefficient we have here if the balanced chemical reaction is not given then the rate of reaction we cannot find out we can find out the rate of individual species but not the rate of the reaction yes understood so if you have any reaction for example you see we have a reaction a b b the rate expression for this reaction is the rate of the reaction is equals to we can write dx by dt which is equals to 1 by a minus of deconcentration of a by dt 1 by b minus deconcentration of b by dt 1 by c plus of deconcentration of c by dt 1 by d sorry 1 by t plus of deconcentration of d by dt okay so this we can write with respect to any reactant or product understood always keep that in mind we always write the reactant whenever you are taking you must take the negative sign here for a product we'll take the positive sign one more definition the last thing today we'll see we'll discuss one question on this okay next class we'll discuss just remind me okay we have to do one question on reaction rate okay it will take some time that's why I'm not giving you enough okay one question one see one term just we need what just we define over here write on reaction lifetime write down it is a time required it is a time required to proceed 98 percent of the completion of reaction so if you look at this relation here more reaction rate lesser will be the reaction lifetime okay so we can write the reaction lifetime lifetime is inversely proportional to the reaction rate so yes so why is it 98 percent yes 98 percent so we'll have a reason for this uh actually none of the reaction goes till 100 percent of completion uh we'll have a mathematical equation for this you will understand this in the next class properly okay but uh if you ask me this question I'll also ask you one question I have drawn this graph correct and none of your okay why not as I got it it'll be an it'll be tending to zero but no yes so the point is for most of the reaction the concentration is decreasing with time okay so when it becomes to almost 98 percent of completion the reaction becomes extremely slow and we assume that okay the reaction is over okay that's why the 98 percent given in the book okay it depends upon the order of the reaction also okay so except one particular order for all the order of the reaction the reaction never goes to 100 completion okay if I give you one small uh you know information here rate expression we can write k times into the concentration to the power n where n is the order of the reaction you know this relation right yes you haven't done this chapter in the school no we haven't done it in school fine anyways so you just assume for a second that this is the rate expression we have for a gives p the product we have so rate we can write down in that form one by that into t of a by dt and all we can also define rate by this that is a law of mass action we'll see that next class okay now you see n is the order of the reaction here okay if this n is zero then what happens if this n is zero rate is independent of rate is independent of concentration concentration so in that case whatever the concentration is rate has nothing to do with that it keeps on going with the same rate and only zero order reaction goes to 100 completion if it is any other value one two or something like that any other value if it is then rate is a function of concentration and concentration decreases with time it can be a straight line like this it can be a curve what would be the graph that we'll see that will understand when we understand the order of the reaction okay but yes rate is a function of concentration it decreases with time so at 98 percent of the completion the rate becomes extremely slow and we assume that the reaction is over that's why the 98 percent we have there yes yes so next class you just remind me we have to do a question on the rate of reaction okay remind me that and then we'll see the other things in this chapter fine okay thank you guys learn for today thank you sir thank you sir