Chapter 3 - Fundamentals of Nonequilibrium Thermodynamics

Abstract

The first attempts to develop nonequilibrium thermodynamics theory occurred after the first observations of some coupled phenomena of thermal diffusion and thermoelectric. This chapter outlines the principles of nonequilibrium thermodynamics for systems not far from global equilibrium. In this region, the transport and rate equations are expressed in linear forms, and the Onsager reciprocal relations are valid. Therefore, sometimes this region is called the linear or Onsager region and the formulations are based on linear nonequilibrium thermodynamics theory. In this region, instead of thermodynamic potentials and entropy, a new property called entropy production appears. The formulation of linear nonequilibrium thermodynamics has proven to be valid and useful for a wide range of transport and rate processes of physical, chemical, and biological systems. Near global equilibrium, the fluctuations decay in time asymptotically toward the equilibrium. In contrast, nonequilibrium states can amplify the fluctuations, and any local disturbances can even move the whole system into an unstable or metastable state. This feature is an important indication of the qualitative difference between equilibrium and nonequilibrium states. Kinetic and statistical models often require more detailed information than is available to describe nonequilibrium systems. Therefore, it may be advantageous to have a phenomenological approach with thermodynamic principles to describe natural processes. In formalism, the Gibbs equation is a key relation since it combines the first and second laws of thermodynamics. The Gibbs relation, combined with the general balance equations based on the local thermodynamic equilibrium, determines the rate of entropy production that helps in analyzing the level of energy dissipation during a process, and in describing coupled phenomena.