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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 18 (2013) pp 144-146
DOI 10.1007/s00897132488

A Kinetic Study of the Dehydration of Copper Sulfate Pentahydrate

Andrew L. Sonnenberger and James E. House*

Department of Chemistry, Illinois Wesleyan University, Bloomington, IL 61701,
Received March 16, 2013. Accepted May 18, 2013.

Published: 31 May 2013

Abstract. Chemical kinetics is taught at an elementary level in general chemistry and at a more advanced level in physical chemistry. However, an examination of undergraduate textbooks reveals that kinetic studies on reactions of solids are discussed very cursorily if at all in these courses even though there are numerous reactions of solids that are important from both an industrial and academic point of view. Consequently, some understanding of the differences between reactions in solids and those in gas or liquid phases is desirable. Copper sulfate pentahydrate, CuSO4•5H2O, is a commonly used example of a hydrated crystalline solid. As a result, it is frequently the object of calculations and experiments in chemistry courses. However, the dehydration of copper sulfate pentahydrate also provides a suitable example for kinetic studies and a discussion of some of the factors affecting reactions in solids. It is known that the loss of water occurs in three steps that involve the loss of 2, 2, and 1 molecules of water, respectively, and the results of kinetic studies on the first two steps are described in this work. In contrast to results presented in previous reports, it was found that for the first step as carried out in this study, the best fitting rate law was the two-dimensional contraction (R2) rate law in almost all runs. For most of the kinetic runs, the second step was found to obey an Avrami (nucleation) rate law with an index of 1.5 (A1.5). Activation parameters for the reactions were evaluated by means of the Arrhenius and Eyring equations, and the effects of some procedural variables were evaluated. These results are discussed to show some of the significant aspects of reactions in solids and to provide an example for heuristic purposes.

Key Words: Laboratories and Demonstrations; physical chemistry

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