Which factor does not change the position of equilibrium?

• A. Increasing concentration of a reactant
• B. Removing a product
• C. Adding a catalyst
• D. Changing temperature

Answer: (C)

The key concept is that a catalyst affects reaction rates, not the equilibrium composition. A catalyst lowers the activation energy for both the forward and reverse reactions, so both rate constants increase by roughly the same factor. Because the equilibrium constant K = k_forward/k_reverse stays the same at a given temperature, the ratio of product to reactant at equilibrium doesn’t change. In other words, the system reaches equilibrium faster, but the final position of the equilibrium remains unchanged.

Other factors do shift the position. Increasing the concentration of a reactant pushes the system toward more product to re-establish equilibrium. Removing product similarly drives the mixture to produce more product. Changing temperature alters the equilibrium constant itself (via thermodynamics), so the position shifts depending on whether the reaction is exothermic or endothermic.