Thermodynamic Explanation
Consider the system at the point it has reached equilibrium. The condition for this is that the chemical potential of the solvent (since only it is free to flow toward equilibrium) on both sides of the membrane is equal. The compartment containing the pure solvent has a chemical potential of . On the other side, the compartment containing the solute has an additional contribution from the solute (factored as the mole fraction of the solvent, < 1) but there also appears an addition in pressure. The balance is therefore:
where denotes the external pressure, the solvent, the mole fraction of the solvent and the osmotic pressure exerted by the solutes. The addition of solute decreases the chemical potential (an entropic effect), while the pressure increases the chemical potential, and thus a balance is reached. Note that the presence of the solute decreases the potential due to being smaller than 1.
Read more about this topic: Osmotic Pressure
Famous quotes containing the word explanation:
“To develop an empiricist account of science is to depict it as involving a search for truth only about the empirical world, about what is actual and observable.... It must involve throughout a resolute rejection of the demand for an explanation of the regularities in the observable course of nature, by means of truths concerning a reality beyond what is actual and observable, as a demand which plays no role in the scientific enterprise.”
—Bas Van Fraassen (b. 1941)