An Approach to Reaction Thermodynamics through Enthalpies, Entropies, and Free Energies of Atomization

Ronald J. Gillespie
Department of Chemistry, McMaster University, Hamilton, ON L8S 4M1, Canada
James N. Spencer and Richard S. Moog
Department of Chemistry, Franklin and Marshall College, Lancaster, PA 17604-3003
J. Chem. Educ., 1996, 73 (7), p 631
DOI: 10.1021/ed073p631
Publication Date (Web): July 1, 1996

Abstract

An alternative to the conventional method of calculating enthalpies of reaction is presented, using enthalpies of atomization in place of enthalpies of formation. This allows the student to see directly that the reaction enthalpies are determined by the difference in bond strengths in the reactants and products. This approach also unifies the model used for considering enthalpies, entropies, and free energies of reaction by calculating all three of these quantities with reference to the same "conceptual intermediate"--the totally atomized state, rather than the stable state of aggregation under standard conditions. This concept--the decomposition of a compound to its constituent gaseous atoms--can be used to discuss not only the thermodynamic parameters but also equilibrium and stoichiometry.

Keywords (Audience):

High School / Introductory Chemistry

Keywords (Feature):

Demystifying Introductory Chemistry

Keywords (Subject):

Calorimetry / Thermochemistry
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  • Received: August 03, 2009

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