Activation energy is defined as which of the following?

• A. The energy released when products form.
• B. The energy difference between products and reactants.
• C. The minimum energy required for reactants to reach the transition state.
• D. The energy required to break all bonds in the reactants.

Answer: (C)

Activation energy is the energy barrier that must be overcome to push reactants to the transition state, the high-energy moment along the reaction path where old bonds are breaking and new bonds are forming. It represents the minimum energy needed for the reaction to proceed from reactants toward products. This energy is not the energy released when products form (the overall energy change of the reaction) and it’s not simply the energy difference between reactants and products. It also isn’t the energy to break all bonds in the reactants; bond-breaking energies can vary and the barrier depends on the specific reaction path. Temperature helps by providing more molecules with enough energy to get over this barrier, and catalysts lower it by stabilizing the transition state.