Chapter 1 - Systems in Thermodynamics of Nonequilibrium Processes

Abstract

The evolution of thermodynamically nonequilibrium systems occurs with respective changes in thermodynamic parameters of the whole system or of its parts. Hence, nonequilibrium states are inherent in the nonequilibrium systems, while the relevant parameters and features of those states can be functions of time and/or space. The nonequilibrium state occurs at the macroscopic level. However, at the microscopic level, fast processes of thermal relaxation run into each microscopic (physically small) part of the system. These processes bring this physically small part of the system to a state that is thermodynamically stable, the relaxation being much faster than the other nonequilibrium processes under consideration. The simplest case of a genuine nonequilibrium system is one with uniform and time-constant temperature and pressure. The thermodynamic force is a pivotal concept in thermodynamics of nonequilibrium processes because of its relationship to the concept of driving force of a particular irreversible process. Evidently, thermodynamic forces arise in spatially inhomogeneous systems with, for example, temperature-, concentration-, or pressure-inhomogeneity. In spatially uniform homogeneous systems, such forces arise either in the presence of chemically reactive components that have not reached thermodynamic equilibrium via respective chemical transformations or at the thermodynamic possibility of some phase transformations.