Exergonically

Exergonically is an adverb used to describe processes or reactions that proceed in an exergonic manner, meaning they release free energy as they occur. In thermodynamics, an exergonic process has a negative change in Gibbs free energy (ΔG < 0) under constant temperature and pressure, indicating that the process is thermodynamically spontaneous in the direction written. Exergonic does not, by itself, imply anything about the speed of the reaction.

A key distinction is between exergonic and exothermic. Exergonic refers to the sign of the Gibbs free energy change, whereas exothermic refers to the sign of the enthalpy change (ΔH). Since ΔG = ΔH − TΔS, a negative ΔG can arise from a negative ΔH (enthalpy-driven) or from a sufficiently large positive entropy change (ΔS > 0) at the given temperature. Therefore, an exergonic process can be exothermic, endothermic, or thermoneutral with respect to heat release.

Kinetics matter for practical behavior: exergonic reactions can be slow if they face high activation barriers, and they may be accelerated by catalysts or enzymes. In biology, exergonic reactions commonly provide energy to drive endergonic processes, often through energy carriers like ATP.

Examples include the hydrolysis of ATP, the oxidation of glucose, and many redox reactions that release free energy. Understanding exergonicity helps explain why certain reaction directions are favored and how energy flow is managed in chemical and biochemical systems.

See also: Gibbs free energy, endergonic reactions, exothermic reactions, metabolism.