Which of the following defines activation energy?

• A. The energy released when new bonds form
• B. The energy required to start a reaction
• C. The energy stored in reactants
• D. The energy of the surrounding environment

Answer: (B)

Activation energy is the minimum amount of energy the reacting molecules must acquire to reach the transition state and start converting into products. It’s like a barrier that has to be overcome for a reaction to proceed. This energy isn’t the energy that gets released later when new bonds form, and it isn’t simply the energy stored in the reactants or the energy of the surroundings—the barrier sits in the reacting system itself. In many cases, a catalyst lowers this barrier, allowing the reaction to proceed with less energy input. So the energy required to start a reaction is activation energy.