An exergonic process is one which there is a positive flow of energy from the system to the surroundings.
"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".
All physical and chemical systems in the universe follow the second law of thermodynamics and proceed in a downhill, i.e., exergonic, direction.
Thus, left to itself, any physical or chemical system will proceed, according to the second law of thermodynamics, in a direction that tends to lower the free energy of the system, and thus to expend energy in the form of work.
The Gibbs free energy is calculated with the Gibbs–Helmholtz equation: where: A chemical reaction progresses spontaneously only when the Gibbs free energy decreases, in that case the ΔG is negative.