How is Le Chatelier's principle used in the Haber Process for making ammonia?

1 Answer
Jun 13, 2018

An old story....


#1/2N_2(g) +3/2H_2(g) stackrel" catalysis "rightleftharpoons NH_3(g)+Delta#

Given that the reaction is exothermic we might assume that at lower temperatures the equilibrium would be shifted to the RIGHT. However at lower temperatures, i.e. room temperature and above, the reaction exhibits an exceptionally SLOW rate, which is unacceptable. Reactor temperatures of #400-500# #""^@C# give a good enuff rate.

Pressure increases would favour the right hand side of the equilibrium, in that a high concentration of reactants should drive the equilibrium to the right hand side as we face the page. And so high PRESSURE favours the forward reaction. I think commercial processes use approx. #200*atm#, which of course requires some pretty sturdy and robust reactors...

There should be many accounts of these considerations on the web. Here is a start.