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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 22 (2017) pp 108-111

Thermodynamics of Dissolution with Applications to Urea in Solvents Composed of Water and 2-Propanol

James E. House

Department of Chemistry, Illinois Wesleyan University, Bloomington, IL 61701,
Received March 22, 2017.Accepted June 7, 2017.

Published: 14 June 2017

Abstract. For a process to be spontaneously feasible, the corresponding value of ∆G must be negative. In the case of a dissolution process, the values for ∆H, ∆S, and ∆G can be determined from data obtained for the solubility as a function of temperature. In this work, the relationships between these parameters are shown in a graphical way. As a case study of the thermodynamics of dissolution, reported data for the solubility of urea in water and 2-propanol and mixtures of the two have been analyzed. In the original report, no thermodynamic values were derived from the data, but the analysis is described in this work to show the effects produced in mixed solvents. For these systems, it was found that the value of ∆H is rather insensitive to the nature of the solvent. The value for ∆S is essentially constant for dissolution of urea in water and 2:1 and 1:2 ratios of water to 2-propanol. However, for dissolution of urea in pure 2-propanol, the value of ∆S is much lower, which causes the value of ∆G to be positive. These observations are discussed in terms of intermolecular interactions between urea and the solvent systems.

Key Words: In the Classroom; physical chemistry; entropy; dissolution; urea; thermodynamics; mixed solvents; free energy; enthalpy

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