The q/T Paradox: Which "Contains More Heat", a Cup of Coffee at 95 °C or a Liter of Icewater?

Ed Vitz
Department of Physical Sciences, Kutztown University, Kutztown, PA 19530
Michael J. Schuman
Department of Chemistry, East Stroudsburg University, East Stroudsburg, PA 18301
James H. Maynard
Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53715
J. Chem. Educ., 2005, 82 (6), p 856
DOI: 10.1021/ed082p856
Publication Date (Web): June 1, 2005
History, Education, and Documentation

Abstract

The q/T paradox is that a liter of icewater at ~0°C contains much more energy than a cup (â¼240 cm3) of coffee at 95°C. In this demonstration, heat is removed from 10 cm3 of water at â¼95°C and 42 cm3 of water at â¼0°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.

Keywords (Audience):

First-Year Undergraduate / General

Keywords (Domain):

Demonstrations

Keywords (Feature):

JCE DigiDemos: Tested Demonstrations

Keywords (Subject):

Calorimetry / Thermochemistry
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  • Received: August 03, 2009

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