Answer is: - delta G.
The change in Gibbs free energy (ΔG), at constant temperature and pressure, is: ΔG=ΔH−TΔS.
ΔH is the change in enthalpy.
ΔS is change in entropy.
T is temperature of the system.
When ΔG is negative, a reaction (occurs without the addition of external energy) will be spontaneous (exergonic).
