Phase diagram

Summary

A phase diagram is a map that shows which phase of a substance is stable for each value of the control variables. The usual control variables are temperature and pressure. Its regions are the phases, and its curves are where two phases coexist and a phase transition happens. Special points are the triple point, where three phases coexist, and the critical point, where a coexistence curve ends. The slopes of the curves are given by the Clausius–Clapeyron relation, and the Gibbs phase rule limits how many phases can meet.