The Thermodynamics of the Critical Point in One‐Component Systems

This review opens with a discussion of the classical description of critical points, and its extension. It is shown that the experimental results do not conform either to the original or to the extended description, although the latter has some features that are to be found both in real fluids and in model systems. However the essential similarity of the results for different fluids has led to the development of the so‐called scaling hypotheses These are empirical relations of simple form which describe the properties of all fluids by means of a suitably scaled equation for chemical potential as a function of density and temperature. They provide concise descriptions of the known singularities in the thermodynamic functions but tell us nothing of the molecular causes responsible for this behaviour. The final section is a brief account of some recent attempts to devise continuum models which have realistic critical points but for which the statistical mechanics is reasonably tractable.