A reaction in which free energy is released. (Contrast with endergonic reaction.)
A spontaneous chemical reaction - one that releases energy.
ex-er-GONE-ik re-AK-shun An energy-releasing chemical reaction. 116
An exergonic reaction is a chemical reaction where the variation of Gibbs free energy is negative IUPAC Gold Book definition http://www.iupac.org/goldbook/E02262.pdf#search='Exergonic%20reaction' Link. This tells us the direction that the reaction will follow.