How is gibbs free energy related to enthalpy and entropy?
Gibbs free energy combines enthalpy and entropy into a single value.
Gibbs free energy is the energy associated with a chemical reaction that can do useful work. It equals the enthalpy minus the product of the temperature and entropy of the system.
G = H – TS
At constant temperature
ΔG = ΔH – TΔS
ΔG predicts the direction of a chemical reaction. If ΔG is negative, then the reaction is spontaneous. If ΔG is positive, then the reaction is non-spontaneous.
When ΔG is less than zero, there is a thermodynamic driving force for the reaction or process in the forward direction (as written). When ΔG is positive, then reactants are favored instead. When ΔG=0 the system is at equilibrium.