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Need clarification!


ChemSiddiqui
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Ok need help with a couple of questions;

 

I am doing past papers and there is this question which I have attempted on my own but am not sure if I did right.

 

A sample of hydrogen gas is held in a pressurised reaction vessel at 350 K and 2 bar claculate ;

(i). the mean speed c(bar) (ii). the collision frequency z

 

It also has given the sigma(H2) =0.27 nm^2

 

(i) I used the mean speed formula (8RT/pi*M)^1/2 to get 1924.83 m/s. The only thing I am not sure about is if I can use this formula(the confusing thing for me is the pressure of 2 bar, not standard pressure).

 

I can calculate z, once i know that i calculated the mean speed right. Can anyone tell me if i did?

 

Second question was to explain why catalyst doesn't alter the position of equillibrium for a chemical reaction.

 

What I think is that catalyst doesnt change the thermodyanmic constant, so that the free energy isnt affected. The relation b/w free energy and thermodynamic constant is ;

 

delta G =-RTlnK

 

again i am slightly confused because the pressure doesnt affect the thermodynamic constant also.

 

Any help please.

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not sure about the first question but the second answer is easy if you simplify your answer to qualitative:

 

a catalyst increases the rate of both the forward and reverse reactions

 

I could give the qualitative answer but its physical chemistry and I have to expalin it quantiatively, not that the question says so but becuase physical chemistry is about that after all isn't?

 

Actually with a bit of reading from a text book I didnt read before, I now know that even though pressure doesnt affect the K, but equillibrium composition does change.

 

thanks for the answer anyway!

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