application/ and ondogie/ The Sign of Work: Endoworkic and Exoworkic Processes Bhairav D. Joshi
State University of New York Coiieoe at Geneseo
edited by: RON DELORENZO
Mlddle Georg~aCollege Cochran. Georgia 31014
Thus, during an exoworkic process, work flows out of the system and during an endoworkic process it flows into the svstem. Furthermore, w is negative for an exoworkic Drocess. q in my courses during the past five Gars. I am happy to re-
port that students now make fewer sign - errors in calculating.
In thermodynamics, the sign convention used for heat, q, is now well established. For exothermic processes, where heat is given off by the system, q is assigned a negatiue sign; for endothermic processes, where heat is absorbed by the system, it is assigned a positive sign. No such uniform convention has been adopted for the sign of work, w. Some textbooks use positive sign for w when work is done opposite convention for w.44 since both y and w are path dependent properties of a process, and since they also can be interconverted by suitahle means, it is desirable that the sign convention be the same for both of these quantities. In other words, heat absorbed by a system and work done on the system should have the same sign. Inasmuch as the sign convention for q is already well established, it makes sense to call, by analogy to heat, all processes where work is done by the system, exoworkic; and all processes where work is done on the system, endoworkic.
This feature presents a collection of descriptive applications and analogies designed to heip students understand some of the difficult ConCeptS frequentlyencountered in chemistry. Contributions that wrii produce a greater appreciation and knowledge of political, religious, economic, historical, and scientific aspects of life are encouraged.
q andlor w.
There are two important consequences of the sign convention described above. (a) The First Law of Thermodynamics now takes this form: AE=q+w
where A&' is the change in the internal energy of a system during the process. (h) The expression for p - u work, i.e., mechanical work, is now given by the expression w = -Jpdu,
so that expansion will be an exoworhic Drocess and comuression, an enduworkic process. The sign of non-mechanical work, if anv, must also be chosen in accordance with the convention described here. The definitions of thermodynamic properties other than work remain unaffected.
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Adamson, A. W., "A Textbook of Physical Chemistry." 2nd ed., Academic Press, Inc.. New York, 1979. Fenn. J. B., "Engines, Energy, and Entropy-A Thermodynamics Primer," W. H. Freeman and ComDanv. San Francisco, 1982. Castellan, G. W., "Physical hem&^," 3rd ed., Addison-Wesley Publishina Comoanv. ,~ ..Readina. -. MA. 1983. Atkins, P. W.. "Physical Chemistry,"2nd ed.. W. H. Freeman and Company. San Francisco. 1982. Berry, R. F.. Rice, S. A,, and Ross. J.. "Physical Chemistry," John Wiley & Sons, New York, 1980. Woore, W. J., "Basic Physical Chemistry," Prentice-Hall, Inc., Englewood Cliffs. NJ, 1983.
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Volume 60 Number 10 October 1983
895
