Question

You and a friend are studying for a chemistry exam. What if your friend says, “Adding an inert gas to a system of gaseous components at equilibrium never changes the equilibrium position”? How do you explain to your friend that this holds true for a system at constant volume but is not necessarily true for a system at constant pressure? When would it hold true for a system at constant pressure?

Short answer

You need to explain to your friend that addition of inert gas does not change the equilibrium only at constant volume but not at constant pressure.

Step-by-step solution

Addition of inert gas at constant volume

Addition of inert gas increases the total pressure at constant volume. But inert gas has no effect on concentrations and partial pressures of reactants and products. Hence, inert gas also has no effect on equilibrium constant. Therefore, addition of an inert gas to a system of gaseous components at equilibrium does not change the equilibrium position at constant volume condition.

Addition of inert gas at constant pressure

Addition of inert gas to the system at constant pressure increases the volume. Therefore, the no of moles per unit volume decreases.To nullify this condition, the equilibrium re-established itself to such a direction where the no of moles is higher. Therefore, addition of an inert gas to a system of gaseous components at equilibrium changes the equilibrium position at constant pressure condition.