An
exergonic process is one in which there is a positive flow of energy from the system to the surroundings. This is in contrast with an
endergonic process. Constant pressure, constant temperature reactions are exergonic
if and only if the
Gibbs free energy change is negative (∆
G < 0). "Exergonic" (from the prefix exo-, derived for the Greek word ἔξω
exō, "outside" and the suffix -ergonic, derived from the Greek word ἔργον
ergon, "
work") means "releasing energy in the form of work". In thermodynamics, work is defined as the energy moving from the
system (the internal region) to the
surroundings (the external region) during a given process.