Phase Diagram
A pressure–temperature plot showing which phase of a substance is thermodynamically stable under any given conditions.
Unit
Pa, K
In depth
Lines on the diagram mark conditions of two-phase equilibrium — fusion, vaporisation and sublimation curves — meeting at the triple point and terminating at the critical point. The slope of the fusion curve reveals whether the solid is denser than the liquid.
Examples in the real world
Water's fusion curve slopes backwards because ice is less dense than water, so pressure melts ice.