D S is positive, since the particles are becoming more dispersed. Therefore, to be spontaneous the D S system must be greater than the D S surroundings . The Third Law of Thermodynamics states that the entropy of a pure, perfectly ordered crystalline substance is 0 at zero Kelvin. Because free energy combines three state functions, H, S, and T, it is also a state function. Gibbs showed that a change tends to occur spontaneously only if the change in free energy, D G, is negative and the D S universe is positive.
Free energy is released in spontaneous reactions.