ABSTRACT
This chapter builds on the concept of chemical potential to develop free-energy expressions for systems undergoing physical transformations. The simplest form of physical transformation is one in which a single component converts from one distinct phase to another. The condition required for coexistence of multiple phases is that their chemical potentials must be identical. Chemical potential and its derivative molar quantities provide a means to quantitatively analyze changes of phase, and to predict phase properties under various conditions. The chapter uses equilibrium thermodynamics to analyze phase transitions and phase stability. It analyzes simple systems where a single chemical component can partition reversibly into different types of bulk materials with distinct properties. The chapter discusses the effects of having multiple components on phase equilibria and develops Gibbs' phase rule as a means to connect the number of components with the number of phases.
