Entropy analyses as a function of the extent of reaction are presented for a number of physicochemical processes, including vaporization of a liquid, dimerization of nitrogen dioxide, and the autoionization of water. Graphs of the total entropy change versus the extent of reaction give a visual representation of chemical equilibrium and the second law of thermodynamics. The mathematical relationship between the total entropy change for the system under standard-state conditions and the equilibrium constant is derived exclusively from entropy analysis. (Contains 16 notes, 2 figures and 3 tables.)