Question

Mention the condition required to maximize the yield of ammonia.

Answer 1

Hint: To answer this question, recall the concept of preparation of ammonia. Consider the conditions required for Haber’s process which affect the equilibrium of this reaction.

Complete step by step answer:
Ammonia is prepared using Haber’s process:
$N_2\left(\text{g}\right)+3H_2\left(\text{g}\right)\stackrel{Fe}{\to }2N{H}_3\left(\text{g}\right)$
The conditions which maximize the yield of ammonia are:
1.Using Le Chatelier’s principle, as the above reaction is exothermic, low temperature will shift the equilibrium to the right leading to a greater yield of ammonia. A temperature of $${450}^{\circ }C$$ will maximise the preparation of ammonia.
2.As there is a decrease in gaseous moles, high pressure on the reaction at equilibrium favours the shift of the equilibrium to the right. A pressure of 200 atm will maximise the preparation of ammonia.
3.To increase the rate of reaction, a catalyst is used and quickly attain equilibrium.
4.The reactants nitrogen and hydrogen gas should be pure to increase the yield of ammonia.

Note:
The change in concentration, pressure, catalyst, inert gas addition, etc. do not affect equilibrium constant. According to Le Chatelier's principle the temperature, concentration, pressure, catalyst, inert gas addition can lead to a shift in equilibrium position only. We know that activation energy is the minimum energy required to start a chemical reaction. Collisions of particles lead to reactions. Only particles that collide sufficiently, can react. Now comes the important point. From the kinetics of a reaction, we know that the rate of a reaction increases with increase in temperature due to more energy and more collisions. But the extent of increase in this rate depends on the “energy of activation” of the reaction which is different for both - the forward and the backward reaction. So, a given increase in temperature leads to an increase in the rate of forward and backward reactions to different extents. So, we can conclude that the value of the equilibrium constant changes with temperature.