Question

In which of the following reactions, the equilibrium remains unaffected in addition to a small amount of argon at constant volume?
A) \[{{H}_{2(g)}}+{{I}_{2(g)}}\rightleftharpoons 2H{{I}_{(g)}}\]
B) \[PC{{l}_{5(g)}}\rightleftharpoons PC{{l}_{3(g)}}+C{{l}_{2(g)}}\]
C) \[{{N}_{2(g)}}+3{{H}_{2(g)}}\rightleftharpoons 2N{{H}_{3(g)}}\]
D) The equilibrium will remain unaffected in all the three cases.

Answer 1

Hint: We know that argon is an inert gas and it doesn’t react, but it can act as a catalyst for many reactions. And it can change activation energy. But in a reversible reaction a catalyst changes the activation energy of both the forward and reverse reactions by the same amount. So, it does not affect the ratio of their rate constant.

Complete-step- by- step answer:
A. The noble gases often do not react with many substances and were historically referred to as the inert gases. An inert gas is a gas that has extremely low reactivity with other substances.
B. Inert gases are used generally to avoid unwanted chemical reactions degrading a sample. These undesirable chemical reactions are often oxidation and hydrolysis reactions with the oxygen and moisture in the air.
C. If we add an inert gas then it can affect the equilibrium constant value because it can change the activation energy of the reaction and which affect the equilibrium constant.
D. When a small amount of argon is added at constant volume, the equilibrium of all the three reactions will remain unaffected as there is no change in the number of moles of either reactants or products.

So from the above explanation we can say that option “D” is the correct option.

Note: If we add at constant pressure volume increases on adding inert gas therefore the equilibrium will shift in forward direction. So, the effect of inert gas addition is different at constant pressure and constant volume.