In equilibrium + – + H The equilibrium constant may change when — Chemical Equilibrium Chemistry Question

💡 Solution & Explanation

# Solution: Factors Affecting Equilibrium Constant For the equilibrium: $CH_3COOH + H_2O \rightleftharpoons CH_3COO^- + H_3O^+$ The equilibrium constant is defined as: $$K_a = \frac{[CH_3COO^-][H_3O^+]}{[CH_3COOH][H_2O]}$$ **Key principle:** The equilibrium constant $K_a$ is a **temperature-dependent quantity only**. **What DOES change $K_a$:** - **Temperature** — Increasing or decreasing temperature shifts the position of equilibrium and changes $K_a$ value itself (Le Chatelier's principle applies to $K$, not just concentrations) **What DOES NOT change $K_a$:** - **Concentration changes** — Adding more reactants or products shifts equilibrium position but $K_a$ remains constant - **Pressure/Volume changes** — For this weak acid dissociation (roughly equal moles of gas), pressure changes don't affect $K_a$ - **Catalyst addition** — Catalysts speed up forward and reverse reactions equally; equilibrium position and $K_a$ remain unchanged - **Addition of spectator ions** — Changes ionic strength slightly but doesn't fundamentally alter $K_a$ for weak acid dissociation **Conclusion:** The equilibrium constant changes **only when temperature changes** (option D).