In kinetics, what is activation energy, and how does a catalyst affect the reaction energy profile?

• A. Activation energy is the energy released by the products; a catalyst increases energy release.
• B. Activation energy is the energy difference between reactants and products; a catalyst raises the energy barrier.
• C. Activation energy is the minimum energy needed for the reaction to proceed; a catalyst provides an alternative pathway with lower activation energy.
• D. Activation energy is the energy stored in the chemical bonds; a catalyst consumes energy to proceed.

Answer: (C)

Activation energy is the minimum energy reactants must have to reach the transition state and start the reaction. On a reaction energy profile, it’s the height of the barrier you must get over to form products. The energy difference between reactants and products is the overall energy change of the reaction, not the activation energy.

A catalyst provides an alternate pathway with a lower activation energy, typically by stabilizing transition states or forming intermediates. This lowers the peak on the energy diagram, so the reaction can proceed more quickly without changing the overall energy change. The catalyst isn’t consumed and doesn’t alter how much energy is released or absorbed by the products; it just makes it easier to reach the transition state, speeding up both forward and reverse reactions under the same conditions.