Equilibrium

Abstract

This chapter begins with a description of thermodynamic equilibrium and its relationship to static equilibrium, defines a global equilibrium state as an idealized actual quasi-equilibrium state. Also a local equilibrium state is described together with the principle of local equilibrium, namely that in a thermodynamic process in which system properties vary in space and time the local equilibrium state equations remain valid. The chapter continues with a review of the mathematics of curves and surfaces needed later and describes a methodology for solving all subsequent thermodynamic problems. This methodology is modified in later chapters to include additional features, but the basic principle remains the same throughout. Finally there is an explanation of how the mechanical equation of state can be written as a differential equation in terms of its measurable first partial derivatives and then integrated to obtain the equation. This idea is then applied to obtain mechanical equations of state for liquids, vaporizable liquids, ideal gases, condensible gases, and mixtures, which includes mixtures of ideal gases such as air and moist air, and most importantly liquid-vapor phase equilibrium mixtures.