Which statement correctly describes how Kc behaves with temperature and concentrations?

• A. Kc is constant at a given temperature and does not depend on concentrations.
• B. Kc decreases with added products.
• C. Kc increases with added reactants.
• D. Kc is constant at a given temperature and does not depend on concentrations.

Answer: (D)

At a given temperature, the equilibrium constant Kc has a fixed value for a reaction. It comes from the definition Kc = [products]^stoichiometric powers / [reactants]^stoichiometric powers when the system is at equilibrium. This value depends only on temperature, not on how much of reactants or products are present. If you add more reactants, the system shifts to produce more products to re-establish the same ratio, and if you add more products, it shifts toward reactants until the ratio matches the same Kc. Only changing the temperature changes the numerical value of Kc.