Final answer:
Adding a catalyst to a reaction in a closed system speeds up the attainment of equilibrium but does not change the equilibrium position, concentrations, or the equilibrium constant.
Step-by-step explanation:
When a catalyst is added to a reaction in a closed system, it does not affect the equilibrium position of the reaction. Such an addition will speed up the rate at which equilibrium is reached, by lowering the activation energy for both the forward and reverse reactions. This acceleration occurs because a catalyst provides an alternative pathway for the reaction with a lower activation energy. However, the catalyst does not change the equilibrium concentrations or the equilibrium constant, because it does not favor one side of the reaction over the other. Therefore, while the time to reach equilibrium may decrease, the composition of the equilibrium mixture remains unchanged.
Le Châtelier's principle explains how a system at equilibrium responds to disturbances (changes in concentration, pressure, volume, and temperature), but adding a catalyst is not considered a disturbance because it alters neither the equilibrium composition nor the equilibrium constant (K). In industrial processes like the synthesis of ammonia, catalysts are often used to increase production rates without changing the chemistry of the equilibrium itself.