What is the effect of a catalyst on the activation energy and the reaction rate?

• A. It raises the activation energy and slows the rate.
• B. It leaves activation energy unchanged and has no effect on rate.
• C. It changes the equilibrium constant and increases rate.
• D. It lowers the activation energy and increases the rate.

Answer: (D)

A catalyst provides an alternate reaction pathway with a lower activation energy, making it easier for molecules to reach the transition state. Because the rate of a reaction depends on how many molecules have enough energy to get over the barrier, lowering the activation energy increases the rate constant (k) through the Arrhenius relationship, so the reaction proceeds faster at the same temperature. Catalysts don’t change the overall energetics of the reaction, so the equilibrium constant and the position of equilibrium stay the same; they simply accelerate both the forward and reverse directions until equilibrium is reached. In short, a catalyst lowers the activation energy and increases the rate.