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A Note on Dalton's Law: Myths, Facts, and Implementation

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William R. Smith

Faculty of Science, University of Ontario Institute of Technology, Oshawa, Ontario, Canada L1H 7K4

Ronald W. Missen

Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 3E5

J. Chem. Educ., 2005, 82 (8), p 1197

DOI: 10.1021/ed082p1197

Publication Date (Web): August 1, 2005

Abstract

The treatment of Dalton's law for gas mixtures commonly includes the improper designation "Dalton's law of partial pressures", rather than the correct "Dalton's law of additivity of (pure component) pressures". It also identifies the pure component pressure as the partial pressure, although these are only numerically equal for a mixture of ideal gases. The situation is clarified by examination of an appropriate statement of the law and definitions, eventually in operational form with reference to mixtures of nonideal gases. Several types of problems are described for which Dalton's law can be used for the approximate calculation of P(T, V, n) or V(T, P, n) of a mixture of nonideal gases. The problems vary depending on the way in which the PVT data for the pure components of the mixture are available, with consequently varying procedures for their solution. In some cases, solution of nonlinear equations is required, which is facilitated by use of metacomputing software. Recommendations are made about which parts of the material presented are suitable for inclusion at two levels of undergraduate instruction: general chemistry courses and physical chemistry and thermodynamics courses.