Question

Which statement(s) about $N_2+3H_2\rightleftharpoons 2N{H}_3$; $\Delta H=-ve$ is/are correct?

• A. At $200$ , the yield of $N{H}_3$ is about 88%
• B. At $500$ , the yield of $N{H}_3$ is about 15%
• C. Reaction occurs at slower rate to attain equilibrium at $200$
• D. Reaction occurs at faster rate to attain equilibrium at $500$
• E. The favourable conditions to get $N{H}_3$ in Haber process are low pressure and high temperature

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A At $200$ , the yield of $N{H}_3$ is about 88%
B At $500$ , the yield of $N{H}_3$ is about 15%
C Reaction occurs at slower rate to attain equilibrium at $200$
D Reaction occurs at faster rate to attain equilibrium at $500$

Option (A),(B),(C),(D) are correct.

$\left(E\right)$ : The favourable conditions to get NH3 in Haber process are high pressure and low temperature.The formation of ammonia is an exothermic reaction with considerable release of heat. The reaction is a reversible reaction, that is, it can proceed both in forward direction (ammonia synthesis) and backward direction (ammonia decomposition). The reaction is accompanied by decrease in volume because there is a decrease in number of moles of gas from 2 to 1.

By Le Chateliers Principle
(i) increasing the pressure causes the equilibrium to shift to the right resulting in a higher yield of ammonia since there is a pressure drop accompanying the transformation.
(ii) decreasing the temperature also causes the equilibrium position to move to the right again resulting in a higher yield of ammonia since the reaction is exothermic (releases heat).