Activation energy is defined as...

• A. Higher Ea slows the rate, while catalysts lower Ea and increase rate.
• B. Higher Ea speeds up the reaction regardless of temperature.
• C. Activation energy has no effect on rate.
• D. Ea determines the reaction mechanism only.

Answer: (A)

Activation energy is the energy barrier that must be overcome for reactants to be transformed into products. At a given temperature, only collisions where the particles have energy at least this high will lead to a reaction. When the barrier is higher, fewer collisions have enough energy, so the reaction rate slows. A catalyst lowers that barrier by offering an alternative pathway with a smaller energy hurdle, which means more collisions become effective and the rate increases. This relationship is captured by the Arrhenius equation, where increasing Ea reduces the rate constant exponentially at a given temperature.

The other statements aren’t correct because activation energy does affect the rate, and higher barriers slow it, not speed it up. Saying it has no effect on rate is false, and claiming Ea only determines the mechanism ignores how Ea governs the energy accessible for reactions and how catalysts can change the pathway.