What effect does a catalyst have on activation energy and reaction rate?

• A. A catalyst changes the overall energy of the reactants and products.
• B. A catalyst slows the reaction by raising activation energy.
• C. A catalyst shifts the equilibrium position of a reaction.
• D. A catalyst lowers the activation energy barrier, increasing reaction rate without changing the final equilibrium.

Answer: (D)

A catalyst works by changing the pathway the reaction follows, lowering the activation energy needed to reach the transition state. With a lower energy barrier, more molecules have enough energy to react at a given temperature, so the reaction rate increases. Crucially, this does not change the overall energy difference between reactants and products, so the final thermodynamic outcome is the same. In reversible reactions, both forward and reverse reactions speed up, leaving the equilibrium composition unchanged. So the best description is that a catalyst lowers the activation energy barrier, increasing the reaction rate without changing the final equilibrium.