What is activation energy?

• A. The energy released during the reaction.
• B. The minimum energy required for particles to react.
• C. The energy of the products.
• D. The energy of the solvent.

Answer: (B)

Activation energy is the minimum energy that colliding particles must have for a reaction to occur. It represents the energy barrier that must be overcome to reach the transition state between reactants and products. If particles collide with energy below this barrier, they don’t react; with enough energy, bonds can break and new bonds form to make products. This energy barrier is not the energy released during the reaction—that energy change is the overall enthalpy change. It’s also not the energy of the products or the solvent. Temperature can increase the number of particles with enough energy to overcome the barrier, and a catalyst provides an alternative pathway with a lower barrier, speeding up the reaction.