Chemical Kinetics part 16

Added: 2026-05-11

[00:00:00]now continuing with the chemical kinetics that is one factor i have already discussed with you that is your catalyst i have discussed with you the catalyst factor now i said you that catalyst what it does catalyst is a substance which alters the rate of the reaction without participating in the reaction it alters the rate of the reaction that means it provides an alternate path to carry out the particular reaction now i have to say little bit more about it i've got it about the catalyst i have to say something more about it now i have already said you that what how the catalyst provides an alternate path that is it lowers the activation energy as it lowers the activation energy so for that particular purpose what you find is that whenever you carry out the reactions with the catalyst what you find is that is nothing but the reaction is faster same thing if it is a negative catalyst listen carefully here if it is a negative catalyst negative catalyst what it will do negative catalyst will the rate of the reaction positive catalyst accelerates the rate of the reaction increases the rate of the reaction but negative catalyst decreases it retards the rate of the reaction so remember that negative catalyst which are known as inhibitors which retards the rate of the reaction let me give you some examples of negative catalyst is that like you have ah ready in class 11 that we are using tetraethyl lead all right they are using tetraethylene which acts as an anti-knocking substance in petrol we are adding a trithylite which acts as an anti-knocking substance what it does it decreases the rate of reactions of that is the petrol the conversion of the petrol because of that similarly that is uh we are using inhibitors correct inhibitors like suppose for the when the blood is not clotting then we we are using the inhibitors which decreases the rate of the reaction similarly the rate of transpiration the transpiration which is taking place in the leaves all right you find the vent the dorsal surface of the leaf it is nothing but it is being coated with wax or naturally naturally it's not somebody's coating naturally is been coated with wax or some hairs is there what is that it acts as an inhibitors it decreases the rate of the reaction so they or they are acts as a negative catalyst when you are preparing oxygen from hydrogen peroxide then the rate of reaction is very fast then you use inhibitors all right it is so fast that you are unable to collect the oxygen gas all right so for that purpose you have to decrease the rate of the reaction there so in this way many negative catalysts are there many positive catalysts are also being there which increases the rate of the reaction like when you're preparing oxygen from potassium chlorate manganese dioxide acts as a partly positive catalyst kclo3 in presence of mno2 will give you kcl plus o2 so manganese dioxide acts as a positive catalyst there in that particular case fine so in this way we are having two types of catalyst basically one is positive catalyst another is your negative catalyst positive catalyst increases the rate of the reaction why because it decreases the activation energy but negative catalyst what it does it increases what you can say increases the activation energy and as a result it decreases the rate of direction because you know activation energy is what is the excess energy which is required to carry out a particular direction that means to require to reach to which level threshold level to reach to the threshold level in threshold level what is being formed activated complex is being formed so if the activated complex is being formed at a higher energy level higher energy level activate complex is found listen carefully activated complex if it is being formed at a higher energy level let us say this is the energy of the reactant and if the activated complex is being formed at a higher energy level then what you'll find is that then the rate of reaction is decreasing all right actually this is the uh what you can say the graph for the actual rate now this much is your energy of the product i can still come down i can still come down we can say that this is your energy of the product we can say that is ep we can say and this is your er clear so in this way what you find is that this is your activation edge you can see now the blue line here you can see this is with catalyst this particular blue line with catalyst so with catalyst means what catalyst it is it is a negative catalyst and the black line is without catalyst without catalyst this one is without catalyst i have not using the catalyst here it is without catalyst the black line is without catalyst here i am not using the catalyst here okay so when i am not using the catalyst you see the activation energy here it is up to this level the activation energy is this all right this is your activation energy when you are not using the catalyst and when you are using the catalyst you can see what happens is that the activation edge is still increased so when activation energy is increased the rate of reaction decreases all right but the same thing if you use suppose this is the actual reaction and now you rub this line you blue line you rub it alright you'll rub this blue line and you make another blue line we can say that another blue line let us make it here this also i am rubbing it another blue line and make it here that is this is the graph you can see without the catalyst this graph you can see now i am drawing a graph here this is the blue line here so this is now with the catalyst so what catalyst is now positive catalyst why it is positive catalyst because because you can see the activation energy here the activation energy is lowered so rate of reaction becomes faster now this is known as the activated complex or the transition state so in case of what you can say positive catalyst activated complex is being formed at a lower energy level and in case of negative catalyst you have seen it the activated complex is being found at higher energy all right so what we find is that as the higher energy level it is being formed so hence the rate of reaction is slower and it is being formed at lower energy level means the rate of reaction is being faster all right in this way catalyst it does not participate in the reaction just it increases or decreases the rate of the reaction depending upon the nature of the catalyst again i repeat positive catalyst increases the rate of the reaction negative catalyst decreases the rate of the reaction all right now next is after that ah if you see that is the characteristics of the catalyst you will find that characteristic the catalyst are always requiring traces my loop quantities very small quantities the catalyst are being required number one number two at the end of the reaction you get back the catalyst how much catalyst you have taken it you get it back that much amount of catalyst and it remains chemically unchanged also we can prove it also it remains chemically unchanged at the end of the reaction how can we prove it let us say we have taken potassium chlorate as i said you kclo3 and i have taken mno2 as a catalyst and give you kcl plus or 2 so 2 kclo3 will give you 2k and plus 3 over here manganese dioxide solid is a catalyst if you won't use manganese just overlapping the rate of reaction will be slower by using manganese dioxide rate of reaction becomes faster so hence mno2 acts as a positive catalyst now let us say i am taken i have taken mno2 as a very small point let us say one gram i can say less than one also possible but one less than one gram it is difficult to weigh isn't it practically so in this way let us say i have taken one gram of mno2 i can i have taken it got it clear now this one gram of mno2 what you do is what you see is that when the reaction is being completed oxygen gas is evolved you will see potassium chloride is a white residue and a black also you can find a substance is remaining behind what i do is that you take this particular black and white residue which you are getting it you take it and you dissolve in water kcl will dissolve in water but not mno2 you filter the solution on filtration you will get back one gram of mno2 on the filter paper how do you know it is one gram of mno2 only not any other substance do a test you will do a test why which will be proved now mno2 the one gram which you got it now you can wait one and find it out one gram that you can see it all right are you following what i'm saying you will get the black and white residue which you'll be getting now at the end of the reaction you dissolving water kcl will dissolve in water leaving behind a black substance i have to prove this black substance is mno2 i can wait and find it out it's one gram that how much i've taken i got it back so that is what i am doing it that black substance i will take and i will react with conch lcl it will give you what is that mncl2 plus water plus chlorine i don't how do i know that if chlorine gas is evolved and the initial gas will be what you can see when amino to react the black substance react with that concentrate a greenish yellow gas is the world proving that the given substance is chlorine and here amino acts as an oxidizing agent so it is being proved by this reaction but the given substance is mno2 because mno2 only reacts to that cl to give you a greenish colored gas that is chlorine no other substance you can survive so in this way we can prove it also that the substance remains chemically unchanged at the end of the reaction now next is what we find is that a catalyst does not alter the delta h of the reaction the change in enthalpy of the reaction catalyst does not alter the free energy of the reaction delta g of the particular reaction but it does not alter the delta g it does not alter the delta h of a particular reaction change in enthalpy neither the changing free energy we can say that a catalyst does not alter the equilibrium of the reaction yes because when i when a catalytic reaction is taking place it not only changes the what you can say the reaction the rate of reaction in the forward direction but also changes the rate of the reaction the backward direction listen carefully when in case of equilibrium reaction in case of reversible reaction a catalyst not only changes the rate of the forward direction but also it changes the rate of the backward direction so ultimately the rate remains the same due to which you find that that it does not alter the equilibrium of the reaction all right the equilibrium of the reaction remains the same because it all not only alters the rate of the forward but also it alters the rate of the backward due to which the reaction remains an equilibrium only all right reaction remains in equilibrium if you use a catalyst what you'll find that you'll you will be attaining you will be getting the equilibrium at a faster rate if you don't use a catalyst you will be finding out that equilibrium will be attained but it is lower right that that's the difference rate the differences okay so this way you came to know the what you can say about the catalyst now what i want to say one more thing to use that that catalyst are again two types homogeneous catalyst and heterogeneous catalysts homogeneous and heterogeneous now what you mean by homogeneous catalyst homogeneous catalyst means when the reactant product and the catalyst are in the same phase it is known as homogeneous catalysis when the reactant product and the catalyst are in the same phase phase means either it will be solid or liquid or gas it is always a homogeneous catalyst if the reactant product and the catalyst are in the different phase ok let us say the reactant is in the gaseous state and the catalyst in the solid state or the reactant is the solid state and the catalyst in the gaseous state in this way when the reactant product in the catalyst are in different phases they are known as it is known as heterogeneous catalysis and the reactant product in the catalyst in the same phase that is on as homogeneous catalyst and given example to you it is a common example you know that so2 gas plus o2 gas you know you have read it in the lower classes this reaction takes place in pt or vanadium pentoxide as a catalyst you can say that you can use it v2o5 or pt as a catalyst you can use it you get it what 2so3 gas 2so2 gas will give you 2so3 gas now this reaction also can be done the same reaction same reaction also can be done by taking nitric oxide gas as a catalyst all right nitric oxide gas is a catalyst i can carry out the same reactions you can say that so it is a heterogeneous catalyst because here this is solid this is a solid you can see whether it is p2 of pt or whether it is v2o5 its a solid and rest all our gaseous here all our gases see this this this this all our gases correct so its a homogeneous catalysis this is heterogeneous catalysis we can say that next is a catalyst but what it does is that it forms an intermediate product and the energy of the intermediate product if it is a positive catalyst it will be lowered for that purpose the rate of reaction becomes faster all right it does not participate in the reaction at the end of the reaction remains all right let me take this example only and explain you all right now here i told you so two plus o two imprints of no gives so3 now first step what happens is that no it's a catalyst it reacts with one of the reactant that is oxygen to form n o two all right this is your intermediate product two n o plus o two gives two n o two because that okay now no2 reacts with another reactant that is so2 another reaction see i'm writing an r1 r2 and this is your intermediate product to form what is that it is nothing but no plus so3 this is your product and this is your catalyst see here no2 here see n n one oxygen four three plus one four sulfur one see so what divided by you have taken nitric oxide as a catalyst you got back nitric oxide so what it does catalyst it lowers the activation energy the first efficiency is what it does it forms an intermediate product and the intermediate product is found at a less energy lower energy rate is being formed due to which the reaction becomes faster so in the second step what happens is that you get so2 and we get the product in this way the catalytic reactions is being carried out so to say okay this particular theory which i have said which is known as intermediate compound formation theory this theory is known as because this is an intermediate product an intermediate compound so this theory is known as intermediate compound formation or intermediate complex formation theory thank you