WordNet
n. a chemical reaction accompanied by the evolution of heat
Wikipedia
An exothermic reaction is a chemical reaction that releases energy by light or heat. It is the opposite of an endothermic reaction.
Expressed in a chemical equation: reactants → products + energy
Usage examples of "exothermic reaction".
The airscrew was driven by an engine powered by a chemical exothermic reaction—.
A rise in the victim's body temperature triggers the bursting of the sacs, and the chemicals in turn undergo a violently exothermic reaction with each other—.
A rise in the victim's body temperature triggers the bursting of the sacs, and the chemicals in turn undergo a violently exothermic reaction with each other -- killing the parasite, damaging the host's surrounding tissues, and stimulating more nearby parasites to go off.