All chemical reactions, even exothermic reactions, need a certain amount of energy to get started. This energy is called activation energy. For example, activation energy is needed to start a car. Turning the key causes a spark that activates the burning of gasoline in the engine.
Answer: Activation energy is the energy required to start a chemical reaction. Some reactions proceed immediately when the reactants are brought together, but for many others, placing the reactants in close proximity is not enough.
