Critical Point | Phase Change - Britannica

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critical point phase change Ask Anything Homework Help Also known as: critical region, critical state Written and fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors History Britannica AI Ask Anything Table of Contents Table of Contents Ask Anything

critical point, in physics, the set of conditions under which a liquid and its vapour become identical (see phase diagram). For each substance, the conditions defining the critical point are the critical temperature, the critical pressure, and the critical density.

Related Topics: triple point critical temperature critical pressure supercritical fluid state (Show more) See all related content

This is best understood by observing a simple experiment. If a closed vessel is filled with a pure substance, partly liquid and partly vapour, so that the average density equals the critical density, the critical conditions can be achieved. As the temperature is raised, the vapour pressure increases, and the gas phase becomes denser. The liquid expands and becomes less dense until, at the critical point, the densities of liquid and vapour become equal, eliminating the boundary between the two phases. If the average density at the start is too low, all the liquid will evaporate before the critical temperature is reached. If the initial average density is too high, the liquid will expand to fill the container.