condition or state of a thermodynamic system, the properties of which do not change with time and that can be changed to another condition only at the expense of effects on other systems. For a thermodynamic equilibrium system with given energy, the entropy is greater than that of any other state with the same energy. For a thermodynamic equilibrium state with given pressure and temperature, the Gibbs free energy is smaller than that of any other state with the same pressure and temperature.