Briefly explain the effect of addition of inert gas on Le-Chatelier's principle.

Explanation

Case I : At constant volume : If an inert gas like argon is added to the equilibrium mixture in a closed vessel, total pressure increases. However, total number of moles of gases also increases. As a result, partial pressure of any gas does not change. Equilibrium is not disturbed.
Case II : At constant pressure : If an inert gas is added at constant pressure (open vessel), volume of the system increases. System tries to increases the number of moles per unit volume, by increasing the total number of moles. As the number of moles increases in the backward reaction, equilibrium gets shifted to the left side.