What drives an endothermic (disfavored by positive delta H) reaction forward? the answer is an increase in entropy (positive delta S). Entropy increases when the number of freely moving particles increases. Total entropy is the sum of the entropy of the system and of its surroundings. You can substitute delta H over T for entropy of the surroundings, and if you multiply both sides by negative T, you get Gibbs' Free energy, delta G
