osmotic pressure, Π 

https://doi.org/10.1351/goldbook.O04344
Excess pressure required to maintain osmotic equilibrium between a solution and the pure solvent separated by a membrane permeable only to the solvent: Π=−R TVA ln⁡aA where VA, aA are the partial molar volume and activity of solvent A for an incompressible fluid. For ideal dilute solutions, Π=cB R T=ρB R TMB, where entities B are individually moving solute molecules, ions, etc., regardless of their nature, cB, ρB are the amount and mass concentration of the solutes, and MB is the mass average molar mass of the solutes. The amount is sometimes expressed in osmol (meaning a mole of osmotically active entities), but this usage and the corresponding term osmolarity are discouraged.
Sources:
Green Book, 2nd ed., p. 51 [Terms] [Book]
Green Book, 3rd ed., p. 59 [Terms] [Book]
Citation: 'osmotic pressure' 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.O04344 RIS BibTex EndNote
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Last revised: February 24, 2014