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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 9 Issue 1 (2003) pp 32-38

Study of a Reversible Gas Phase Reaction: An Integrated Physical Chemistry Project

João Pedro Malhado, Miguel Tavares, and Mário N. Berberan-Santos*

Centro de Química-Física Molecular, Instituto Superior Técnico, 1049-001 Lisboa, Portugal,
Received July 25, 2003. Accepted October 16, 2003.

Published online: 26 November 2003

Abstract. The reversible gas phase reaction dinitrogen tetroxide to nitrogen dioxide is very suitable for an integrated physical chemistry project incorporating thermodynamics, statistical mechanics, spectroscopy, and kinetics. Furthermore, nitrogen oxides are molecules of current interest given their important role in atmospheric chemistry. Only relatively common equipment and chemicals are required for the experiment. It consists of the synthesis of NO2 and of the study of the UV–vis electronic absorption spectrum of the NO2/N2O4 gas mixture as a function of temperature. From the analysis of the spectra, the absorption spectra of the pure constituents are obtained as well as the temperature dependence of the equilibrium constant of the reaction. From this dependence, the enthalpy and the entropy of the reaction are obtained. The values are analyzed and compared with statistical mechanical calculations. The kinetics of the reaction is also discussed.

Key Words: Laboratories and Demonstrations; physical chemistry; thermodynamics; statistical mechanics; spectroscopy; kinetics

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Updated 9/8/2004 change on page 36 DrH0=57.2 kJ mol–1 from DrS0=57.2 kJ mol–1

Issue date: February 1, 2004

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