Derive a single thermodynamic function which would allow the determination of a spontaneous reaction. Discuss why and how every substance possess free energy, but it is the changes in free energy, delta G, that are measured in chemical and physical reactions. The Gibbs fee energy formula is presented, viewed on a graph, and determined how each result on the graph determines whether the reaction will occur spontaneously or not. Spontaneous reactions are determined by whether G is less than zero, equal to zero, or greater than zero