Question

Describe the favourable conditions for the manufacture of ammonia by habers process

Answer 1

If you look at the reaction of Ammonia;

N2(g) + 3H2(g) <==> 2NH3(g) + energy

its an exothermic reaction where volume or number of moles are decreasing, so according to Le Chatelier’s principle; the favorable conditions for ammonia production are:-

High Pressure (As number of moles are decreasing)

Low Temperature (As the reaction is exothermic)

But as you know the rate of a reaction increases as the temperature increases, so to increase the rate you have to increase the temperature but to maximize the yield you have to decrease the temperature (since the reaction is exothermic) thus to produce a good yield of ammonia you have to choose your operating temperature such that the rate and yield both are maximum.

Yield can also be increased with the help of two reactors, one operating at high temperature to increase the rate of the reaction and second reactor operating at lower temperature to shift the equilibrium of the reaction and for maximization of the yield of ammonia.

Regarding the catalyst, Fe/Mo is the catalyst used in the Haber’s process.

Since, the catalyst itself requires at-least a temperature of 400 degree C to be efficient, thus this minimum temperature should be maintained.