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  Home > JCE Print > Journal of Chemical Education > Issues > 1997  > March  >
Chemical Education Today
Letters
An Exceptional Theoretical Process
Rubin Battino
Wright State University, Dayton, OH 45435

Scott E. Wood
Illinois Institute of Technology, Chicago, IL 60616

Cover
March 1997
Vol. 74 No. 3
p. 256

Full Text
The article by Belandria (1) has so many problems that we hardly know where to start. Neither the "exceptional" process nor the conditions are sufficiently rigorously defined to do a proper analysis. Thus, we are forced to start from scratch and define the changes of state which occur and the nature of the systems and their surroundings so that we can do meaningful calculations.

Consider one mole of an ideal monatomic gas of constant Cv of 12.47 J mol-1 K-1 confined to an adiabatic container sealed by a frictionless weightless piston. This is container A and TAi = 1500 K, VAi = 123.086 L, and PAi = 101.33 kPa.

Container A is connected to container B by a rigid adiabatic wall. Container B is also adiabatic and rigid and initially contains one mole of an ideal monatomic gas. TBi = 373 K, PBi = 101.33 kPa, and VBi = 30.607 L.

Replace the wall between A and B with a massless rigid diathermic partition. Now, reversibly and isothermally compress the gas in A until the temperature in B reaches 1500 K. The pressure in B is now 407.49 kPa. The heat absorbed by gas B (from A) is given by Delta U = nCv Delta T = 14,054 J. Since all of the walls (except the separating partition) are adiabatic, then the 14,054 J must come from A. A simple calculation shows that VAf = 39.883 L and PAf = 312.68 kPa derived from the work done on A to produce 14,054 J.

The entropy change in A is Delta SA = {14,054/1500 = -9.37 J mol-1 K-1. The entropy change in Bi is obtained from Delta SB = nCvln(TBf /TBi) = 17.35 J mol-1 K-1. The entropy change of the universe is Delta Suniv = Delta SA + Delta SB = +7.98 J mol-1 K-1 for the work done on compressing the gas in A plus heating the gas in B.

Please note that the only way the compression in A may occur isothermally is via a reversible process. This is the minimum work of compression. And, entropy changes must be calculated along reversible paths. If you assume the final state for A indicated by the author then 17,289 J are generated. Continuing, if you assume the author's final state for B, then 14,054 J are absorbed. What happens to the excess heat? The author's numbers are incompatible. There are no surprises here and no exceptions to the laws of thermodynamics.

Literature Cited

1. Belandria, J. I. J. Chem. Educ. 1995, 72, 116-118.

More Information
*  Citation
Battino, Rubin; Wood, Scott E. J. Chem. Educ. 1997 74 256.
*  Keywords
*  History
Created:
Last Updated:
July 29, 1999
June 23, 2005
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