What is the effect of a catalyst on a reaction rate diagram?

• A. It raises the activation energy and slows the reaction.
• B. It lowers activation energy; the reaction reaches the transition state faster.
• C. It changes the products formed.
• D. It increases the overall energy of the system.

Answer: (B)

A catalyst works by providing an alternative pathway with a lower activation energy, so the reactants reach the transition state more readily and the reaction proceeds faster. On a reaction rate diagram, this shows as a lower energy peak for the catalyzed path, while the final energy of the products remains the same as in the uncatalyzed path. This means the overall energy change of the reaction is unchanged, but the barrier to start is smaller, speeding up the rate. The other ideas would imply changing the products or adding energy to the system, which a catalyst does not do.