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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 10 Issue 1 (2004) pp 5-9

Volume-Expansion Work: pdV or pextdV?

Sebastian G. Canagaratna

Department of Chemistry, Ohio Northern University, Ada, OH 45810,
Received August 4, 2004. Accepted October 31, 2004.

Published online: 16 December 2004

Abstract. Volume-expansion work involves a pressure term. The treatment of this pressure term in chemistry texts is not uniform and likely to be misleading. It is shown that the definition of volume-expansion work in mechanics leads to the choice of the surface pressure as the required pressure. To what extent this definition can be usefully applied to an irreversible expansion is also discussed. It is shown that a claim that the pressure in the theoretical expression for work cannot be the surface pressure is invalid. The implications of these results for teaching are also considered.

Key Words: In the Classroom; physical chemistry; thermodynamics; work; pressure; volume; PV=nRT

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Issue date: February 1, 2005

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