3. Thermodynamic Equilibrium in Isolated and Isentropic Systems

In isolated systems, the condition of equilibrium following the release of an internal constraint is the maximum of the entropy function – according to Postulate 2. The condition of equilibrium in isentropic systems, the minimum of energy is derived from this principal using mathematical relations concerning the two functions. In the rest of the chapter, detailed treatment of thermal, mechanical and chemical equilibrium is given, both in isolated and isentropic (adiabatic) systems. In addition to the equilibrium condition that the corresponding intensive quantities are equal in the subsystems of the composite system, the calculation of the relevant quantities specifying the equilibrium state is also described. Detailed discussion of the intensive properties temperature and chemical potential is also presented with respect to equilibrium, and their change towards equilibrium.