ABSTRACT
Thermodynamic equilibrium of a system is defined when thermal, mechanical and mass exchange equilibrium are achieved. The equilibrium states are generally those that either maximize or minimize some thermodynamic function. The entropy is shown to be a maximum for isolated systems in equilibrium and is obtained from the second law of thermodynamics. The Helmholtz function is a minimum for fixed volume systems interacting isothermally with environment while the Gibbs-free energy is a minimum for systems in equilibrium in contact with pressure and temperature reservoirs. The direction of evolution towards equilibrium is discussed using these functions. In the case of thermal equilibrium, the temperatures are obtained to be the same while for mechanical equilibrium the pressures are equaled. When mass exchange takes place either at phase boundary or otherwise and the chemical potential remains the same at equilibrium. The chemical potential for a single component system equals the specific Gibbs function per mole of it. Multicomponent systems and the Gibbs Duhem equation linking changes in temperature, pressure and chemical potential are discussed.
