critical pressure(redirected from critical pressures)
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critical pressure[′krid·ə·kəl ′presh·ər]
the pressure of a substance or mixture of substances in the critical state. At pressures less than the critical pressure, the system may dissociate into two equilibrium phases, a liquid and a gas. At the critical pressure the physical distinction between the liquid and gas is lost, and the substance undergoes transition to a single-phase state. Thus, the critical pressure may also be defined as the limiting (highest) saturated vapor pressure under conditions of existence of the liquid and vapor phases.
The critical pressure is a physicochemical constant of the substance. (For values of the critical pressure pc of a number of substances, see Table 1 in CRITICAL POINT.) The critical state of mixtures differs in the dependence of the critical pressure on the composition and thus exists not at a single critical point but on a curve on which all points are characterized by critical values of pressure, temperature, and concentration.