osmotic coefficient, ϕ

https://doi.org/10.1351/goldbook.O04342
Quantity characterizing the deviation of the solvent from ideal behaviour referenced to Raoult's law. The osmotic coefficient on a molality basis is defined by: ϕ=μA∗−μAR T MA ∑imi and on an amount fraction basis by: ϕ=μA∗−μAR T ln⁡xA where μA∗ and μA are the chemical potentials of the solvent as a pure substance and in solution, respectively, MA is its molar mass, xA its amount fraction, R the gas constant and T the temperaure. The latter osmotic coefficient is sometimes called the rational osmotic coefficient.
Sources:
Green Book, 2nd ed., p. 51 [Terms] [Book]
PAC, 1994, 66, 533. (Standard quantities in chemical thermodynamics. Fugacities, activities and equilibrium constants for pure and mixed phases (IUPAC Recommendations 1994)) on page 546 [Terms] [Paper]
Citation: 'osmotic coefficient' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.O04342 RIS BibTex EndNote
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