Question

The most favourable condition for the manufacture of $N{H}_3$ is:

• A. high temperature and high pressure
• B. low temperature and low pressure
• C. high temperature and low pressure
• D. low temperature and high pressure

Answer 1

Answer: (D)

$N_2$ and $H_2$ combine to give ammonia as follows:
$\underset{1vol}{N_2(g)}+\underset{3vol}{3H_2(g)}\rightleftharpoons \underset{2vol}{2N{H}_3(g)}$
$\Delta H=-92.38kJmo{l}^{-1}$
This reaction is exothermic and is accompanied by decrease in volume.
So favourable conditions for forward reaction, according to Le-Chatelier's principle are :
(i) low temperature (ii) high pressure
(iii) excess of $N_2$ and $H_2$