Gibbs Free Energy and the Spontaneity of Chemical Reactions

The change in Gibbs free energy associated with a chemical reaction is a useful indicator of whether the reaction will proceed spontaneously. Since the change in free energy is equal to the maximum useful work which can be accomplished by the reaction

then a negative ΔG associated with a reaction indicates that it can happen spontaneously. This is consistent with the usual chemistry convention of treating work done by the system as negative work. Most common reactins can be assessed for spontaneity under standard conditions by looking up the associated thermodynamic quantities for each of the reactants and products. For non-standard conditions one can make use of the the expression for ΔG in terms of the other thermodynamic potentials