Thermodynamic State

the state in which a thermodynamic system exists. Thermodynamic states are characterized by a set of macroscopic properties, which determine the internal properties of a system in that state and the interaction of the system with external bodies. These properties include temperature, pressure, volume, electric polarization, and magnetization.

Among the thermodynamic state properties there exists a specific number of independent variables, equal to the number of thermodynamic degrees of freedom of the system; the remaining variables can be expressed in terms of the independent variables. Thus, in the equation of state for an ideal gas, pV = RT, two variables—for example, temperature T and volume V —are independent, and the third, the pressure of the gas p, can be found from T and V (R is the gas constant). In thermodynamics, a distinction is made between equilibrium states and nonequilibrium states; the latter are studied in the thermodynamics of irreversible processes.