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Defining the Heats of Reactions Using the Concept of ‘Extent of Reaction’

Connecting Thermochemistry Taught in General Chemistry with Advanced Physical Chemistry

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Abstract

The conventional way heats of reactions are introduced in a general chemistry course presents ambiguities that are not addressed much later until the students take an advanced physical chemistry course. To avoid this confusion, it is much more convenient to use the idea of the ‘extent of a reaction’ to define the heats of reactions, starting right from a course on general chemistry. This article presents the derivation of how the heats of reactions may be defined based on the extent of a reaction, highlighting along the way some common but tricky assumptions made which are usually not highlighted in textbooks/or by instructors, even in an advanced physical chemistry course.

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Suggested Reading

  1. An excellent introduction to the concept of the extent of reaction — G D Peckham, The extent of reaction: Some nuts and bolts, J. Chem. Educ., 78, pp.508–509, 2001.

  2. Donald McQuarrie, John D. Simon, Molecular Thermodynamics, University Science Book, Sausalito, California, USA, 1997.

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  3. Peter Atkins, Julio de Paula, Atkins’ Physical Chemistry, Oxford University Book, Oxford, UK, 2014.

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  4. Ira N. Levine, Physical Chemistry, McGraw-Hill, New York, USA, 2009.

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  5. Robert J. Silbey, Robert A. Alberty, and Moungi G. Bawendi, Physical Chemistry, John Wiley & Sons, Inc. Hoboken, USA, 2005.

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Acknowledgements

The author acknowledges one of his students, V. C. Thamarai Valli, for asking a question in her CHM121 course. This article is a consequence of her question. He also acknowledges the anonymous referee for the wonderful suggestion of including the idea of ξ in this work, and suggesting that we explicitly point out the current problematic definitions used in popular textbooks.

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Authors and Affiliations

  1. Department of Chemistry, Indian Institute of Science Education and Research, Tirupati, Andhra Pradesh, 517 507, India

    Raghunath O. Ramabhadran

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  1. Raghunath O. Ramabhadran
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Correspondence to Raghunath O. Ramabhadran.

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Raghunath O. Ramabhadran is an Assistannt Professor at IISER Tirupati. His research interests include computational astrochemistry, development of new methods in computational thermochemistry, and scientific pedagogy.

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Ramabhadran, R.O. Defining the Heats of Reactions Using the Concept of ‘Extent of Reaction’. Reson 27, 753–767 (2022). https://doi.org/10.1007/s12045-022-1370-x

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  • DOI: https://doi.org/10.1007/s12045-022-1370-x

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