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In the Classroom
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Tested Demonstrations
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The q/T Paradox: Which "Contains More Heat", a Cup of Coffee at 95°C or a Liter of Icewater?
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Ed Vitz
Department of Physical Sciences, Kutztown University, Kutztown, PA 19530
Michael J. Schuman
Department of Chemistry, East Stroudsburg University, East Stroudsburg, PA 18301
checked by James H. Maynard
Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53715
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June 2005
Vol. 82 No. 6
p. 856
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| Abstract |
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The q/T paradox is that a liter of icewater at ~0°C contains much more energy than a cup (~240 cm3) of coffee at 95°C. In this demonstration, heat is removed from 10 cm3 of water at ~95°C and 42 cm3 of water at ~0°C by adding each to a measured sample of liquid nitrogen. The heat removed from the water boils the N2(l), and the quantity of liquid nitrogen that is evaporated by boiling is determined. The quantity of heat that was absorbed is calculated from the heat of vaporization of liquid nitrogen and found to be about 10,000 J in the case of the hot water and 25,000 J in the case of the icewater. Calculations of the energy content of water, taking into account the variability of the heat capacity, are provided.
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| Supplement |
All experimental data and analysis are available in an Excel spreadsheet.
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 Contents |
JCE2005p0856W.xls (Microsoft Excel)
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| Download |
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| More Information |
Citation |
Vitz, Ed; Schuman, Michael J. J. Chem. Educ. 2005 82 856.
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Keywords |
Calorimetry / Thermochemistry; Demonstrations; First-Year Undergraduate / General; Heat Capacity; High School / Introductory Chemistry; Phases / Phase Transitions / Diagrams; Physical Chemistry; Thermodynamics
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History |
Created:
Last Updated: |
April 27, 2005
May 6, 2005
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| Home > JCE Print > Journal of Chemical Education > Issues >
2005
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856
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