Which quantity remains constant for a given temperature: Kc or Q?

Which quantity remains constant for a given temperature: Kc or Q?

• A. Kc
• B. Q
• C. Both
• D. Neither

Answer: (A)

At a fixed temperature, the equilibrium constant Kc is constant for a given reaction because it depends only on temperature and the reaction’s stoichiometry, describing the ratio of product activities to reactant activities at equilibrium. The reaction quotient Q uses the actual, momentary concentrations and can vary as the system moves toward equilibrium. As concentrations change, Q changes until the system reaches equilibrium, where Q equals Kc. If the temperature changes, Kc would change as well. So, for a given temperature, Kc remains constant.

At a fixed temperature, the equilibrium constant Kc is constant for a given reaction because it depends only on temperature and the reaction’s stoichiometry, describing the ratio of product activities to reactant activities at equilibrium. The reaction quotient Q uses the actual, momentary concentrations and can vary as the system moves toward equilibrium. As concentrations change, Q changes until the system reaches equilibrium, where Q equals Kc. If the temperature changes, Kc would change as well. So, for a given temperature, Kc remains constant.