## Wikipedia - Osmotic coefficient osmotic coefficient, $$\phi$$

https://doi.org/10.1351/goldbook.O04342
Quantity characterizing the @D01650@ of the @S05746@ from ideal behaviour referenced to @H02783@. The osmotic @C01124@ on a molality basis is defined by: $\phi =\frac{\mu _{\text{A}}^{*}- \mu _{\text{A}}}{R\ T\ M_{\text{A}}\ \sum _{\begin{array}{c} i \end{array}}m_{i}}$ and on an amount fraction basis by: $\phi =\frac{\mu _{\text{A}}^{*}- \mu _{\text{A}}}{R\ T\ \ln x_{\text{A}}}$ where $$\mu _{\text{A}}^{*}$$ and $$\mu _{\text{A}}$$ are the chemical potentials of the solvent as a pure substance and in solution, respectively, $$M_{\text{A}}$$ is its molar mass, $$x_{\text{A}}$$ its amount fraction, $$R$$ the @G02579@ and $$T$$ the temperaure. The latter osmotic @C01124@ is sometimes called the rational osmotic @C01124@.
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]