Raoult's law
Raoult's law concerns the vapour pressure of the solvent above a solution. This is always lower than the vapour pressure of the pure solvent, and the form of the law first proposed by François-Marie Raoult in 1887[1][2] was that the fractional lowering of the vapour pressure of the solvent is proportional to the amount fraction of solute.[note 1] A more general statement, which allows for the dissociation of the solute, is that the vapour pressure is proportional to the amount fraction of solvent.
Both of these statements hold only for dilute solutions, and a solution which obeys these simple forms of Raoult's law is termed an ideal solution. Limited non-ideal behaviour can be accounted for by taking fugacities instead of vapour pressures, and this approach is used to define the activity of the solvent in a solution.[3]
Notes and references
Notes
- ↑ As Raoult pointed out, this statement is only strictly true if the solute does not dissociate in solution. A formal treatment of the effects of dissociation was provided by van 't Hoff.
References
- ↑ Raoult, F.-M. Loi générale des tensions de vapeur des dissolvants. C. R. Hebd. Seances Acad. Sci. 1887, 104, 1430–33, <http://gallica.bnf.fr/ark:/12148/bpt6k30607.image.f1429.langEN>. English translation
- ↑ Raoult, F.-M. Remarques sur un calcul de M. Van t' Hoff relatif à la tension de vapeur des dissolutions. C. R. Hebd. Seances Acad. Sci. 1887, 105, 1857–59, <http://gallica.bnf.fr/ark:/12148/bpt6k3061j/f857.image.langEN>.
- ↑ Standard quantities in chemical thermodynamics. Fugacities, activities and equilibrium constants for pure and mixed phases (IUPAC Recommendations 1994). Pure Appl. Chem. 1994, 66 (3), 533–52. DOI: 10.1351/pac199466030533.
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