Exothermic Reaction Definition

An exothermic reaction is a chemical reaction that produces heat (has a negative ΔH). In other words, the activation energy needed to initiate the reaction is less than the energy it releases.

Examples of exothermic reactions include neutralization reactions, the Haber process, the thermite reaction, and combustion reactions.

The opposite of an exothermic reaction is an endothermic reaction. Endothermic reactions absorb more heat from their surroundings than they release. Exothermic and endothermic reactions are types of exergonic and endergonic reactions. In exergonic and endergonic reaction, the net energy (whether it be heat, light, or sound) is greater (exergonic) or less (endergonic) than the energy needed for the reaction to proceed.