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Raoult's Law, Water Activity and Moisture Availability in Solutions
Author(s) -
CAURIE M.
Publication year - 1983
Publication title -
journal of food science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 150
eISSN - 1750-3841
pISSN - 0022-1147
DOI - 10.1111/j.1365-2621.1983.tb10812.x
Subject(s) - mole fraction , chemistry , thermodynamics , vapor pressure , activity coefficient , mass fraction , fraction (chemistry) , solvent , chromatography , organic chemistry , aqueous solution , physics
A rationalization of Raoult's law has led to the conclusion that water activity (a w ) is a joint solution property of vapor pressure, solute and solvent concentrations. It is shown from this that a w is not a measure of the absolute value of the mole fraction of water as indicated by Raoult's law but a measure of only a fraction of the mole fraction of water remaining free in solution available and unbound to solute molecules. The law is shown to overestimate this water activity (a w ) at all dilutions by an amount equal to the product of the mole fraction of solute and the lowered relative vapor pressure the solute generates in solution.