Critical Point
The unique combination of temperature and pressure at which the liquid and gas phases of a substance become indistinguishable.
Formula / equation
(T_c, p_c)
Unit
K, Pa
In depth
At this point the densities of liquid and vapour converge, the meniscus vanishes and surface tension falls to zero. The phenomenon of critical opalescence — intense light scattering from density fluctuations — makes the transition visible. Beyond it lies the supercritical region.
Examples in the real world
Water's critical point is 374 °C and 218 atm; carbon dioxide's is a far more accessible 31 °C and 73 atm.