Critical Point Definition

Critical Point Definition

In a phase diagram, the critical point or critical state is the point at which two phases of a substance initially become indistinguishable from one another. The critical point is the end point of a phase equilibrium curve, defined by a critical pressure T_p and critical temperature P_c. At this point, there is no phase boundary.

Also Known As: critical state

Critical Point Examples

The liquid-vapor critical point is the most common example, which is at the end point of the pressure-vapor temperature curve distinguishing a substance's liquid and vapor. The meniscus between steam and water vanishes at temperatures above 374°C and pressures above 217.6 atm, forming what is known as a supercritical fluid.

There is also a liquid-liquid critical point in mixtures, which occurs at the critical solution temperature.