Generally defined in terms of changes in free energy: ΔF = ΔH – TΔS, where H = enthalpy, T = absolute temperature, S = entropy. In a mixture of reactants, if ΔF is less than 0 a reaction may take place spontaneously, whereas if ΔF is positive energy must be supplied to the system for a reaction to occur at all. In geochemistry, the sign and magnitude of ΔF are important. The sign indicates whether a given reaction can occur spontaneously, and the magnitude indicates how far the reaction can go before equilibrium is attained.
Subjects: Earth Sciences and Geography.