The tendency of the molecules in a fluid, as a result of all forces acting on them, to leave a given site in the body; the escaping tendency of a fluid, as in diffusion, evaporation, etc. [L. fuga, flight]
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fu·gac·i·ty fyü-'gas-ət-ē n, pl -ties the vapor pressure of a vapor assumed to be an ideal gas obtained by correcting the determined vapor pressure and useful as a measure of the escaping tendency of a substance from a heterogeneous system
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fu·gac·i·ty (fu-gasґĭ-te) [L. fugacitas, from fugere to flee] a measure of the escaping tendency of a substance from one phase to another phase, or from one part of a phase to another part of the same phase. The logarithm of the fugacity is proportional to the chemical potential, measured by the correction for the deviation of the behavior of a gas from ideal.Medical dictionary. 2011.