Energy of activation is defined as?

• A. The total energy of the reactants
• B. The energy stored in ATP
• C. The energy released by a reaction
• D. The energy needed to cause molecules to react with one another

Answer: (D)

Activation energy is the energy barrier that must be overcome for reactants to reach the transition state and form products. It represents the minimum energy input needed to get the reaction started, i.e., the difference between the energy of the reactants and the high-energy activated complex along the reaction pathway. This is not the total energy of the reactants, nor the energy stored in ATP, nor the energy released by the reaction. Catalysts like enzymes lower this barrier, speeding up reactions by reducing the required energy input without changing the overall energy change of the process. Temperature can influence how many molecules have enough energy to reach that transition state.