Equations of State and Phase Diagrams

Abstract

Equations of state (for example, the ideal gas equation) contain three (or more) variables and should therefore be graphically represented by three (or more!)-dimensional diagrams. Three-dimensional diagrams and models are quite common for single-phase systems, but multiphase systems are usually displayed in projection or simply sketched. Here, we present a three-dimensional phase diagram based on authentic experimental data for a unary system, carbon dioxide, with its solid, liquid and vapor phases. Such an authentic diagram appears not to have been presented before, and may improve the understanding of phase relationships.