Chapter 3 - Fundamentals of Nonequilibrium Thermodynamics

Abstract

Physical systems identified by permanently stable and reversible behavior are rare. Unstable phenomena result from inherent fluctuations of the respective state variables. Near a global equilibrium, the fluctuations do not disturb the equilibrium; the trend toward equilibrium is distinguished by asymptotically vanishing dissipative contributions. In contrast, nonequilibrium states can amplify the fluctuations, and any local disturbances can even move the whole system into an unstable or metastable state. 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. Such an approach is the formalism used in nonequilibrium thermodynamics to investigate physical, chemical, and biological systems with irreversible processes. In the 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. Onsager developed the basic equations of the nonequilibrium thermodynamics theory, and Casimir, Meixner, and Prigogine refined and developed the theory further. This chapter outlines the principles of nonequilibrium thermodynamics for systems not far from a 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.