An [blank_start]exothermic[blank_end] reaction is a chemical reaction that [blank_start]releases[blank_end] energy by light or heat. It is the opposite of an [blank_start]endothermic[blank_end] reaction.. Expressed in a chemical equation: reactants → products + energy!
As exothermic reactions release [blank_start]heat[blank_end] energy, the product of the [blank_start]reaction[blank_end] is the heat, with whatever the heat is caused by being the reactant.
In [blank_start]reversible[blank_end] reactions, the reaction in one direction will be exothermic and the reaction in the other direction will be endothermic.