When the mixture of gases leaving the catalyst chamber is cooled, only ammonia becomes a liquid and it can be removed easily. Unchanged nitrogen and hydrogen are recycled. High pressure favours a good yield of ammonia, so the pressure chosen is the highest that is economically practical. The reaction is exothermic in the forward direction, so high temperature reduces the yield of ammonia in the equilibrium mixture, but increases the rate at which equilibrium is reached. The temperature chosen is a compromise between these two factors.
Ammonia is used in the manufacture of fertilisers and of nitric acid.