ABSTRACT
This chapter discusses the critical phenomena at the liquid-gas transition, with particular emphasis on the description given by the Van der Waals equation. The Van der Waals equation gives a qualitatively accurate account of the phase diagram of fluids, exhibits properties such as the law of corresponding states and gives a mean-field theory of the liquid gas critical point. The chapter provides a rapid review of the fundamental thermodynamics of fluids and phase equilibria. Two phases of matter with different symmetry must be separated by a line of transitions. This reflects the fact that one cannot continuously change symmetry; that is, a symmetry is either present or absent. A liquid and a solid are believed to be always separated by a line of transitions. The chapter describes the spatial correlations in a fluid near the critical point, again within the framework of mean field theory.
