<P> An exothermic reaction is a chemical reaction that releases energy by light or heat . It is the opposite of an endothermic reaction . </P> <P> Expressed in a chemical equation: reactants → products + energy . Exothermic Reaction means "exo" meaning releases and "thermic" means heat . So the reaction in which there is release of heat with or without light is called exothermic reaction . </P> <P> An exothermic reaction is a chemical or physical reaction that releases heat . It gives net energy to its surroundings . That is, the energy needed to initiate the reaction is less than the energy released . </P> <P> When the medium in which the reaction is taking place gains heat, the reaction is exothermic . When using a calorimeter, the total amount of heat that flows into (or through) the calorimeter is the negative of the net change in energy of the system . </P>

When is heat released in a chemical reaction