Subject:
Note that the diagram has three general areas corresponding to the three states of
matter––solid, liquid, and gas. The line from A to C represents the solid’s change in vapor
pressure with changing temperature, for the sublimation equilibrium. The A-to-D line represents
the variation in the melting point with varying pressure. The A-to-B line represents
the variation of a liquid’s vapor pressure with varying pressure. The B point shown on this
phase diagram is called the critical point of the substance, the point beyond which the gas
and liquid phases are indistinguishable from each other. At or beyond this critical point, no
matter how much pressure is applied, the gas cannot be condensed into a liquid. Point A is
