How is La Chatelier's principle useful in the chemistry industry? What is the effect of temperature on the equilibrium constant?

1 Answer
Jun 15, 2017

Consider dinitrogen fixation.........


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

This is probably the most important chemical reaction on the planet. Without such a process, there would be NO nitrogenous fertilizer with which to grow food.......The problem with this reaction is that we have to overcome very strong #N-=N# and #H-H# bonds, and catalysis, usually closely guarded industrial secrets, can enable some small yield of #NH_3(g)#.

Now the only thing this reaction has got going for it is that the product gas, #NH_3(g)#, is CONDENSABLE, while the reactant gases, are relatively incondensable. And we could use Le Chatelier's principle to exploit these properties.

And thus if we use a cold finger to CONDENSE the ammonia, the liquid ammonia is removed from the equilibrium, and the equilibrium re-establishes itself by moving to the right as we face the page.........Good turnovers of product can be achieved thereby. Does Le Chatelier's principle apply with respect to this aspect of the reaction?

And note with regard to the given reaction, the exothermic nature of the reaction would suggest that lower temperatures would be favourable. Unfortunately, at these lower temperatures, the reaction would have an unacceptably low rate. Modern processes trade off the temperature with acceptable yields, and are able to achieve high turnovers.