Which factor directly lowers the activation energy of a reaction?

• A. Adding a catalyst
• B. Increasing temperature
• C. Increasing concentration
• D. Increasing surface area

Answer: (A)

Direct lowering of the activation energy comes from providing an alternative reaction pathway with a lower energy barrier. A catalyst achieves this by stabilizing the transition state or forming different intermediates, so the energy required to reach the transition state is reduced. This changes the rate without altering the overall thermodynamics of the reaction.

Other factors change how often or how effectively molecules collide or how much energy those collisions have, but they don’t change the intrinsic energy barrier. Increasing temperature increases the fraction of molecules with enough energy to reach the barrier, speeding the reaction while keeping Ea the same. Increasing concentration or surface area raises collision frequency or the available reactive area, also increasing rate without altering Ea.