Describ chemistry of manufacture of ammonia by Haber's process and discuss conditions for good yield of ammonia.

Explanation

Ammonia is manufactured from `N_2` and `H_2` by the Haber process. The reversible reaction involved in the process is as follows.
`N_2 (g) + 3H_2 (g) hArr 2NH_3 (g) , Delta_(tau) H^@ =- 92.2 KJ "mol"^(-1)`
In accordance with Le Chatelier.s principle, the conditions for maximum yield of `NH_3` are,
(i) High pressure : About 200 atm. This is because the forward reaction proceeds with a decrease in volume.
(ii) Optimum temperature : About 700 K. A lower temperature, will no doubt increase the yield of `NH_3`, but it will also decrease the rate of reaction. As such a much longer time will be needed to attain equilibrium.
(iii) Catalyst : As the temperature used is not high, a catalyst (iron oxide + `K_2 O + Al_2 O_3)` is used to increase the rate of reaction, so that equilibrium is attained in a shorter time.
The flow chart for the process is given below.