Thermodynamic Equilibrium

Abstract

THE modern analytical method in chemical thermodynamics, although in many respects vastly superior to the old method of the isothermal reversible cycle, is unfortunately marred by the absence from standard text-books of a concise and exact statement of the chemical condition of equilibrium. In its place we are offered a number of restricted conditions from which a choice must be made. One of these, for example, is the familiar but not always true statement that for an infinitesimal change at constant temperature and pressure of a system in reversible equilibrium, the change of the Gibbs's free energy is zero (dG_T,P = 0). Since, however, a single condition of equilibrium which is valid for any infinitesimal change may easily be obtained and is, in fact, one of the most important generalizations of thermodynamics, it seems worth while to place it on record.