 Next factor we have effect of inert gas or addition of inert gas what happens okay so addition of inert gas we can have at constant volume and at constant pressure okay so first we will see at constant volume if you add inert gas then what happens okay so suppose we talk about the partial pressure of any component in a reaction it is equals to we can say NA the number of moles of A RT by B right RT by B and we can also write this equals to XA the mole fraction of A into the total pressure PT okay further you see if you add an inert gas inert gas suppose the number of moles is Ni and mole fraction is Xi okay so the partial pressure of A when you add inert gas into this then again we can write the mole fraction of A into total pressure okay and mole fraction we can write the number of moles of A by the total number of moles NT and A by NT into PT right and PT is equals to what we can write further you see and A by NT this NT includes the includes the moles of inert gas here right here if you write down XA is equals to NA by NT into PT this NT we do not have any what we say inert gas present okay so PT is equals to NA by NT and PT we can write total number of moles NT RT by B because B does not change total number of moles becomes NT so whatever here we have total number of moles the same number of moles we have here so hence what happens this number of moles number of moles gets cancelled and the partial pressure again becomes NA RT by B so what we can say the partial pressure of A in presence of inert gas or without inert gas is same only NA by NA RT by B NA RT by B if volume is constant right it means the partial pressure is not affected by the addition of inert gas right hence we can say the addition of inert gas at constant volume does not have any effect okay addition of inert gas the statement you write down the addition of inert gas at constant volume does not have any effect now you see what happens at constant pressure at constant pressure here we have again three possible cases the first one is when delta NG is equals to 0 where delta NG is equals to 0 the the suppose the reaction is A gives B the smallest one and taken and hence KP or KC for this reaction if I write down that is the concentration of B by concentration of A and which we can write number of moles of B divided by the volume number of moles of A divided by volume you see this is independent of the volume term and B by NA right it means once you add inert gas and pressure is constant right that does not affect the equilibrium constant KC because addition of inert gas at constant volume will change the volume right volume of the system because inert gas will also have some volume correct when since KC is independent of volume hence it is independent of addition of inert gas so we can say at this condition addition of inert gas won't affect the equilibrium condition okay delta NG is equals to 2nd case is what delta NG is greater than 0 reaction we can write A G gives B gas plus C gas okay KC for this reaction we can write number of moles of B number of moles of C number of moles of A into volume so as addition of inert gas you know volume increases volume increases so intake decreases to maintain the same value of KC similar thing we can discuss in pressure right so NV decreases V increases NA decreases NA decreases means forward reaction okay third case is what C when delta NG is less than 0 for example A gas plus B gas gives C gas so KC for this reaction is a number of moles of C by number of moles of A number of moles of B into B as volume increases addition of inert gas volume increases so what happens NC decreases to maintain KC and NC decreases means what backwards so this is the three condition of addition of inert gas constant pressure we have these three conditions possible at constant volume we do not have any effect of inert gas okay okay so our last thing we'll discuss here is the physical equilibrium physical equilibrium it is actually the application of leach athlete's principle first thing actually we have to discuss here the effect of pressure on boiling and melting point of water okay effect of pressure on boiling and melting point of water first you see H2O liquid converts into H2O vapor gas okay so my point is we are talking about the boiling point here liquid to vapor conversion we have so our discussion is all about what happens on the effect of pressure volume point increases or decreases okay so what happens you see as pressure increases then volume decreases right to maintain this volume decreases and which one has higher volume gaseous system or liquid system you know liquid system has lesser volume and gas H2O gas has higher volume gases molecules has higher volume than liquid and then solid right hence when pressure decreases sorry increases volume decreases this means the reaction has tendency to go towards the lesser volume and hence once what we can say since liquid system has lesser volume so backwards shift is there backwards pressure increases volume decreases liquid has lesser volume than gas then reaction goes in backward direction correct now backward shift is there it means what in this particular reaction it is it does not have any meaning backward or forward shift why because you can write down the reaction at this also H2O gas gives H2O liquid so liquid to gas conversion we cannot say it is always backward because for this reaction it will be forward for this reaction it will be backward right so it depends what reaction is written so we are not talking about in terms of backward and forward shift here I have just written this with respect to this reaction if you write this one then it is forward shift okay so keep that in mind so we won't discuss here in terms of backward and forward shift we discuss here what happens on boiling point if pressure increases so how do we understand that like I said here if you increase the pressure more water forms because it is going in this direction so more water forms in means means what the conversion of liquid into vapor is not easier then vapor into liquid right pressure increases and more water is forming it means liquid to vapor conversion is difficult vapor to liquid conversion easier that's why this is going backward and more amount of water is forming it means what we can say that the boiling point of water increases because when boiling point increases then only this conversion becomes difficult if it decreases if it decreases it means this to this conversion is easier that is what happening so what happens as pressure increases boiling point increases as pressure decreases boiling point of water decreases okay you can also understand this fact by one particular example you must have heard about that at higher altitude cooking becomes difficult right so why is that difficult because we know at higher altitude the pressure is less atmospheric pressure is less okay and the boiling point defines when the vapor pressure of the system is equals to the atmospheric pressure then only the vapor starts escaping into the atmosphere when it is equal to the atmospheric pressure the moment the vapor pressure of water becomes equals to the atmospheric pressure right that time only the equilibrium is maintained and that pressure is vapor pressure exerted by the water molecule is the vapor pressure of water molecule and then only evaporation and boiling takes place okay so when this pressure is less at lesser temperature only the pressure becomes equal if it is more then you have to provide more heat so that more vapor forms and more pressure will be there from the vapor side okay so that is that is what happens higher altitude pressure decreases pressure decreases then boiling point also decreases pressure increases boiling point decreases lower altitude pressure increases boiling point increases okay so don't remember this backward and forward shift remember what pressure increases so boiling point increases decreases then boiling point decreases now the last thing we will discuss here is the melting point melting point of water so suppose we have H2O solid which is ice converts into H2O liquid which is water okay now ice has low density we all know water ice is the only solid which has lower density than liquid okay low density and high density higher density the lower this is higher right so density means what mass by volume so as pressure increases what happens volume decreases volume decreases means density density increases means what happens as you increase the pressure the reaction goes towards the molecule which has more density increases means with increase in pressure we have forward shift again I am telling you the same thing don't remember forward or backward shift here also forward shift it means what more water forms more H2O liquid forms this means the melting is easier here it means the melting point decreases right so as pressure increases melting point decreases as pressure decreases melting point increases this you must remember this is the only case where this relation we have any other solid if you take solid and suppose diamond and graphite you take right so in that case it will be reverse okay because solid ice is the only solid we have which has lower density than its liquid that is water right so volume point increases with pressure melting point decreases with pressure okay this is it for Lee-Chantelier's principle okay we have also discussed the physical equilibrium these two points is very important as far as any competitive exam like Jay mains need or any other exam if you consider these two points are very important not given in all the books I would arrest you to memorize these two things okay if you understand it's fine otherwise I have explained the concept of this okay you can understand it easily but if you can mug up these two points that will help you in exam okay thank you