 Okay, third factor is effect of pressure, effect of pressure, okay. So effect of pressure for this, we cannot generalize of one particular relation of pressure and the direction of the reaction, okay. But this effect depends upon the type of reaction you have, okay. Means we can have basically three types of reaction. The first type of reaction we have where delta Ng is equals to 0. This is one type of reaction. Another type is what? When delta Ng is greater than 0 or less than 0, okay. So any of these things possible, correct. So delta Ng is equals to 0, one by one we will discuss all those. So what you can write? Suppose the reaction we have A gas plus this reaction, delta Ng is greater than 0. So what is the equilibrium of equilibrium relation? Kp is equals to partial pressure of C, partial pressure of D into partial pressure of D, okay. And we know partial pressure is equals to mole fraction into total pressure. So further we can write this as, and you see this Pt will get cancelled. And the expression of Kp, if you see it will be mole fraction of C into D A into P. This is the mole fraction relation. You see this Kp is independent of pressure term here, right, there is no pressure term present. So in this type of reaction where delta Ng is equals to 0, pressure does not have any effect on the equilibrium, okay. So pressure won't change the equilibrium state of this type of reaction, okay. Another one, B, delta Ng is greater than 0, okay. Suppose the reaction is A gas gives B gas and C gas, this is the reaction we have, delta Ng greater than 0. Now similarly we can write down the equation of Kp is equals to X of B into X of C divided by X of A into Pp, like this you can write, okay. So there is a pressure term present here. So what happens as Pt increases, as Pt increases, okay, Kp won't change, right, because we know equilibrium constant depends only upon temperature. This Kp won't change means the ratio of this is constant. If you change the pressure also, then also this ratio coming out to be constant so that the Kp won't change. Now this ratio to be constant what happens as Pt increases, then we can say what two things possible, XB decreases and XC decreases or we can also say that XA increases, what possibility we have, okay. If numerator increases, then denominator has to increase to maintain the ratio. If numerator decreases, denominator has to decrease to again maintain the ratio, okay. Now when this XA increases, when this thing is possible, XA is what, mole fraction of A, right. So mole fraction of A increases when the reaction will go in forward, sorry, backward direction, then only the number of moles of A increases and hence XA increases. So in this condition what we can write as Pt increases, backward shift is there, right and here as Pt decreases, then forward shift, forward shift is there, okay. XA has to decrease and XA will decrease when the reaction goes in forward direction, right. So this is the relation of pressure and the direction of the reaction forward or backward, okay. We can also understand one more thing here directly we can do, okay that we will see after the discussion of the third point here and whenever delta Ng is equals to 0, pressure would not have any effect, this you must remember, the third factor is what, when delta Ng is less than 0, C, when delta Ng is less than 0, suppose the reaction is A gas plus B gas and this gives C gas, delta Ng is less than 0, right. So that expression for Kp for this equation is XC divided by XA into XB into 1 by Pt, if you write down you will get this only. So here what happens as Pt increases, as Pt increases XC has to increase to maintain the ratio and XC increases it means what, forward shift, Pt decreases, XC has to decrease it means backward shift, backward shift, right. So forward and backward, so like this mathematically you can understand that what is the effect of pressure in this kind of reaction, okay. Directly also you can do you just see the reaction, right. Suppose if pressure is increasing, we know pressure and number of moles are directly proportional, so when pressure increases you have to decrease the number of moles so that the equilibrium is maintained, right. So pressure decreases, pressure increases, number of moles you have to decrease. Pressure decreases, number of moles you have to increase, means as pressure increases the reaction shift in that direction where we have the lesser number of moles. For example, in this reaction you see as you are increasing the pressure, so product side we have two moles of the gaseous product and one mole of the gaseous reactor. So, as pressure increases backward shift is there, reaction goes towards the lesser number of moles. So, pressure increases backward shift, pull down what pressure decreases forward shift ok. So, this is done this also you can discuss number of moles, here you see pressure if you increase correct, reaction goes towards lesser number of moles that is product forward pressure increases forward pressure you decrease reaction goes towards more number of moles backward right to backward means backward product is there ok. So, like this you can do this questions directly in the exam ok. Fourth factor we have effect of catalyst, first of all you see catalyst does not take part in the reaction, catalyst does not take part in the reaction, so what does it do it just increases it just increases or decreases the rate of forward or backward reaction it just increases or decreases the rate of forward or backward reaction. So, what we can say in presence of catalyst we can achieve the equilibrium in a lesser time or more time means we can slow down the reaction or we can increase the rate of the reaction we can have the reaction which is going like processing with a very high rate depending upon the nature of the catalyst. So, catalyst actually does not take part in the reaction it just affect the rate of the reaction rate of the reaction when I say it means both forward reaction and backward reaction. So, it affects the rate of the reaction two types of catalyst we have negative and positive catalyst in general in our syllabus we have positive catalyst only if they have not mentioned negative catalyst and only catalyst if they have given it means we have to understand or take positive catalyst correct. So, positive catalyst what happens it increases the rate of the reaction whether it is forward or backward it increases the rate of the reaction. So, it is positive catalyst increases the rate of the reaction and negative catalyst if it is there it slows down the reaction and decreases the rate of forward and backward reaction. When I say positive catalyst it increases the rate of forward and backward reaction. So, if I explain this with a graph suppose the reaction goes like this it is the reactant and it is the product the energy of reactant and product. Now, you see this reactant forms the activated complex and then it converts into product it can be endothermic isothermic anything possible. So, this graph is without catalyst normal thing now when you add a positive catalyst into this then the reaction goes like this in presence of a positive catalyst it goes like this. So, this graph the blue one is with positive catalyst and the red one is with negative catalyst sorry the white one is with negative catalyst. So, this yellow one is without catalyst so, what happens here corresponding to this the energy is what here we have activation energy. So, positive catalyst what happens it decreases the activation energy for forward reaction and as well as the activation energy for backward reaction. So, positive catalyst decreases ea activation energy for forward and backward reaction and hence the reaction goes with a faster rate the energy value is not that great. So, all these molecules will cross this energy value easily because the activation energy decreases and hence the reaction rate is fast. So, and hence the equilibrium achieved in a lesser time negative catalyst is just opposite it increases the activation energy for forward and backward reaction and that is why the reaction slows down. So, what happens here it increases the activation energy for forward and backward reaction and the reaction slows down that is the effect of catalyst we have it does not effect the initial and final condition you see the reaction with or without catalyst the initial and final condition is same only right where is the whatever concentration we have in this reaction without catalyst the same concentration at equilibrium we have in presence of catalyst with catalyst whether it is negative or positive ok. So, what we can you know summarize about this particular this particular fact effect is the presence of catalyst does not alter the initial and final condition of a reaction ok means initial final condition means the concentration of those reactant and product is same with or without catalyst that will not change. So, what it does it decreases or increases the activation energy of a reaction and hence it affects the rate of forward and backward reaction ok. So, in presence of positive catalyst the reaction goes with a faster rate and achieve equilibrium in a lesser time right with negative catalyst the reaction slows down forward and backward both and equilibrium achieve in more time right time requires more here for to achieve the equilibrium of this kind of reaction ok that is very important always remember catalyst does not take part in any reaction ok.