Haber Process!?

Hello just a bit confused about the haber process, increasing the pressure would increase the number of molecules of ammonia produced since its 4 reactant molecules producing just 2 product molecules so really by increasing the pressure you increase the number of molecules thus the higher the yield?

Thanks a lot just want to make sure

From John Wood

Reply 1

charco

Study Forum Helper

you are just really stating Le Chatelier's principle - a system at equilibrium will respond to a change of conditions in such a way as to oppose that change.

if you increase the pressure the system can release the pressure (ths opposing the increase) by moving to the side with the fewer number of gas moles - in this case to the side of the ammonia:
N2 + 3H2 <==> 2NH3

In mathematical terms this can be shown by considering the concentrations at equilibrium (or the partial presssures) - if you increase the pressure on the system by decreasing the volume then the concentrations in the equilibrium law expression with the higher powers (i.e. those with the highest stoichiometry in the balanced equation) will have more effect on the value of the equilibrium constant Kc and the concentrations have to change to re-establish the original value of Kc

In the Haber process equilibrium:

Kc = [NH3]^2/[N2]

^3

if the volume is decreased then the value of the denominator (bottom part of the fraction) will decrease by more than the value of the numerator (top part of the fraction)in the fraction - the system restores the value of Kc by producing more NH3 using up some of the denominator and increasing the numerator

Reply 2

geekypoo

N₂ + 3H₂ ----> 2NH₃

As the pressure increases, le chateliers principle If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.
If the temperature is increased the dynamic equilibrium will shift to decrease the temperature, So a high pressure with a low temperature will give the largest yeild, i think

Reply 3

charco

Study Forum Helper

note that in the case of a pressure change the value of Kc is not affected (just the concentrations) but in the case of a temperature change Kc has a different value!