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In the Classroom
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A Thermodynamic Analysis to Explain the Boiling-Point Isotope Effect for Molecular Hydrogen
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D. Blane Baker
Division of Natural Sciences, Ouachita Baptist University, Arkadelphia, AR 71998-0001
Byron K. Christmas
Department of Natural Sciences, University of Houston-Downtown, One Main Street, Houston, TX 77002-1001
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June 2000
Vol. 77 No. 6
p. 732
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| Abstract |
The analysis reported provides an explanation for the
boiling-point isotope effect observed for molecular
hydrogen isotopes (H2, D2, and
T2); that is, an explanation for the increase
in normal boiling point with increasing molecular mass.
The standard enthalpy of vaporization
 is
shown to depend on molecular mass, and
itself is related to temperature via a standard solution
to the Clausius-Clapeyron equation. Simplification of the
solution, at standard pressure, yields an expression for the normal boiling point that depends on molecular mass. An evaluation of the expression, using constants obtained from two of the boiling points in the series, allows a prediction of the third boiling point. As an example, the predicted boiling point of ditritium is 24.9 K, in close agreement with the observed value of 25.0 K.
See Letter re: this article.
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| More Information |
 Citation |
Baker, D. Blane; Christmas, Byron K. J. Chem. Educ. 2000 77 732.
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Keywords |
Isotopes; Molecular Properties / Structure; Phase Transitions / Diagrams; Physical Chemistry; Teaching/Learning Theory/Practice
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History |
Created:
Last Updated: |
April 25, 2000
April 15, 2005
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Link to Letter added (April 2004).
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