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Thermodynamics of Air: Reinterpreting the Method of Clement and Desormes
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Abstract
The well-known Clement-Desormes method for heat capacity ratio employs a large bottle of air, an oil manometer, and a rubber pressurizing bulb. The air sample at slightly elevated pressure undergoes a rapid adiabatic expansion followed by isochoric warming back to room temperature. The usual calculation of the ratio is sidestepped in favor of a new interpretation which recognizes that for air, the work done in the rapid expansion must equal the heat absorbed when the gas returns to room temperature.
These quantitites and the accurately known differences between the PVT states permit a direct determination of the heat capacity Cv.
Students are exposed to the concept of irreversible work, path independence of DeltaE, and experimentally use the equation DeltaE = Q + W. Since air is diatomic and closely obeys the ideal gas law, the heat capacities and various partial differential coefficients can be calculated and compared with experimental results.
Keywords (Audience):
Upper-Division UndergraduateKeywords (Domain):
Physical ChemistryKeywords (Pedagogy):
Hands-On Learning / ManipulativesKeywords (Subject):
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- Received: August 03, 2009
ACS
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