Question

In a vessel ${N_2},{H_2}$ and $N{H_3}$ are at equilibrium, some helium gas is introduced into the vessel so that total pressure increases while temperature and volume remain constant. According to Le Chatlier’s principle, the dissociation of $N{H_3}$ :
(A) Increases
(B) Decreases
(C) Remains unchanged.
(D) Equilibrium is disturbed.

Answer 1

Hint : Le Chatlier’s principle is also known as equilibrium law. It depends upon the concentration, temperature and pressure of the system. It states that when any of the above quantities are changed, the system responds and restores a new equilibrium.

Complete step by step answer:
${N_2} + 3{H_2} \rightleftharpoons 2N{H_3}$
It is known as Haber-Bosch process. In this synthesis, a balance between temperature and pressure is found as low temperature and high pressure is maintained. According to the question, total pressure increases while temperature and volume remain constant.
So, by Le Chatlier’s principle, when total pressure increases, the dissociation of ammonia remains unchanged as there is no change in the volume. It will show change if the partial pressure of the system is changed.
Thus, option C. (remains unchanged) is the correct option of the given question.

Additional Information
-Increase in the concentration of reactants will shift the equilibrium towards the right side and decrease in the concentration of reactants will shift the equilibrium towards the left. This is supported by collision theory as well.
-Increase in pressure by decreasing the volume of the system shifts the equilibrium towards the side containing less number of moles. Formation of an additional number of moles is favored by decrease in pressure by increasing the volume of the system. But when the total number of moles on reactant and product side is equal in number in a gas-phase reaction, there is no effect of change in volume or pressure.
-To understand the effect of temperature, consider heat as one of the reactants for endothermic reactions and one of the products for exothermic reactions. For an endothermic reaction, lowering the temperature will shift the equilibrium to the left and increasing it will shift the equilibrium to the right. It will be reversed for an exothermic reaction.

Note:
Le Chatlier’s principle is applicable to pure solids and liquids. This principle is important because it helps us to shift the equilibrium to the side we want. An inert gas will have no effect on the equilibrium of the reaction according to this principle.