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A Simplified Method for Measuring the Entropy Change of Urea Dissolution. An Experiment for the Introductory Chemistry Lab

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Charles A. Liberko and Stephanie Terry

Department of Chemistry, Cornell College, Mount Vernon, IA 52314-1098

J. Chem. Educ., 2001, 78 (8), p 1087

DOI: 10.1021/ed078p1087

Publication Date (Web): August 1, 2001

Section:

History, Education, and Documentation

Abstract

The enthalpy change, equilibrium constant, Gibbs free energy change, and entropy change of the dissolution of urea in water were determined in a guided-inquiry lab experiment. Introductory-level students were able to obtain quite satisfactory thermodynamic values for the dissolution of urea using minimal equipment and a very simple procedure. The enthalpy change of dissolution was determined with a simple coffee-cup calorimeter. Students then directly determined the concentration of a saturated solution of urea simply by measuring the amount of urea used and the total volume of the solution as prepared in a graduated cylinder. The equilibrium expression for the dissolution of urea can be simplified to K = [urea]. With the enthalpy change and the equilibrium constant determined experimentally, the free energy change and enthalpy change for the process are readily calculated.

Keywords (Audience):

First-Year Undergraduate / General

Keywords (Domain):

Laboratory Instruction

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Thermodynamics

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