دورية أكاديمية
Expansion Work without the External Pressure and Thermodynamics in Terms of Quasistatic Irreversible Processes
| العنوان: | Expansion Work without the External Pressure and Thermodynamics in Terms of Quasistatic Irreversible Processes |
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| اللغة: | English |
| المؤلفون: | Schmidt-Rohr, Klaus |
| المصدر: | Journal of Chemical Education. Mar 2014 91(3):402-409. |
| الإتاحة: | Division of Chemical Education, Inc and ACS Publications Division of the American Chemical Society. 1155 Sixteenth Street NW, Washington, DC 20036. Tel: 800-227-5558; Tel: 202-872-4600; e-mail: eic@jce.acs.org; Web site: http://pubs.acs.org/jchemeduc |
| Peer Reviewed: | Y |
| Page Count: | 8 |
| تاريخ النشر: | 2014 |
| نوع الوثيقة: | Journal Articles Reports - Descriptive |
| Education Level: | Higher Education Postsecondary Education |
| Descriptors: | Science Instruction, Chemistry, Thermodynamics, Equations (Mathematics), Scientific Concepts, College Science, Misconceptions, Teaching Methods |
| DOI: | 10.1021/ed3008704 |
| تدمد: | 0021-9584 |
| مستخلص: | We demonstrate that the formula for irreversible expansion work in most chemical thermodynamics textbooks does not apply during the expansion process. Instead of the "external pressure" P[subscript ext], the pressure P[subscript sys,mb] on the piston or other moving boundary (hence the subscript mb), which is nearly equal to the system pressure P[subscript sys], should be used in the integral over volume. This formula only requires that P[subscript sys](V) and T are well defined, that is, a system of uniform P and T ("uPT") undergoing a "uPT process", which may be irreversible. An instructive example is an expanding gas accelerating a bullet horizontally and performing work without a conventional external pressure. We emphasize that dw = -P[subscript sys,mb] dV ˜ -P[subscript sys] dV is the only useful formula for infinitesimal PV work during a uPT process. The quasistatic approximation P[subscript sys,mb] = P [subscript sys] and dw = -P[subscript sys] dV is usually excellent and enables analyses of irreversible uPT processes, for example, in heat engines; friction in the surroundings and a large piston mass improve the approximation. Slow chemical reactions at constant T and P are quasistatic, and many equations in advanced chemical thermodynamics apply specifically to uPT or quasistatic processes. We show that the equality dS = dq[subscript irr]/T applies in irreversible quasistatic processes without composition change. In short, with well-defined P and T at constant composition, the simple equations for reversible processes are usually excellent approximations even when the process is irreversible. |
| Abstractor: | As Provided |
| Entry Date: | 2014 |
| رقم الأكسشن: | EJ1031159 |
| قاعدة البيانات: | ERIC |
Find this issue from the American Chemical Society | تدمد: | 0021-9584 |
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| DOI: | 10.1021/ed3008704 |