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  Home > JCE Print > Journal of Chemical Education > Issues > 2007  > July  >
In the Classroom
Mass-Elastic Band Thermodynamics: A Visual Teaching Aid at the Introductory Level
William C. Galley
Department of Chemistry, McGill University, Montreal, Quebec H3A 2K6, Canada
Cover
July 2007
Vol. 84 No. 7
p. 1147
Abstract
Five spontaneous isothermal processes arising from combinations of enthalpy and entropy changes can be presented in a visual manner to students being introduced to chemical thermodynamics. The five spontaneous processes illustrated are (a) purely energy changes and entropy changes in the system due to a falling mass and contracting ideal elastic band, respectively, and (b) three remaining processes derived from the coupling of a mass and elastic band together. The five spontaneous processes initially appear identical in that the basic components of each system are hidden from view. However, based on hypothetical measurements of q obtained first when each process occurs irreversibly (qirr) and then repeated performing maximum work, or reversibly (qrev), the systems and the processes occurring within them can be readily distinguished. The distinction arrived at from the values of q is readily confirmed when covers are removed revealing the inner workings of each system. The demonstration helps students appreciate how measured heat effects obtained under appropriate conditions are employed to obtain the changes in the thermodynamic parameters that are associated with the spontaneous events. Analogies can then be drawn between these mass-elastic band processes and common spontaneous molecular events such as chemical reactions and phase transitions.
More Information
*
Citation
Galley, William C. J. Chem. Educ. 2007, 84, 1147.
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Keywords
Analogies / Transfer; Calorimetry / Thermochemistry; Demonstrations; First-Year Undergraduate / General; Physical Chemistry; Second-Year Undergraduate; Thermodynamics
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History
Created:
Last Updated:
5/29/2007
6/7/2007
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