The total amount of energy which is either used up or released during a chemical reaction. Gibbs free energy (delta G) = (delta H) - t (delta S): where (delta H) is the change in enthalpy, calculated by adding up the amount of energy released or used up to break or form chemical bonds during the reaction; t is the temperature at which the reaction took place; and (delta S) is the change in entropy, or amount of disorder, that occurs in the molecules involved during the reaction.