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Article

Understanding the Clausius–Clapeyron Equation by Employing an Easily Adaptable Pressure Cooker

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Monica Galleano , Alberto Boveris and Susana Puntarulo

Physical Chemistry, School of Pharmacy and Biochemistry, University of Buenos Aires, C1113AAD, Buenos Aires, Argentina

J. Chem. Educ., 2008, 85 (2), p 276

DOI: 10.1021/ed085p276

Publication Date (Web): February 1, 2008

Section:

History, Education, and Documentation

Abstract

This article describes a simple and inexpensive laboratory exercise developed to understand the effect of pressure on phase equilibrium as described by the Clausius–Clapeyron equation. The only piece of equipment required is a pressure cooker adapted with a pressure gauge and a thermometer in the lid, allowing the measurement of the pressure and the temperature of the chamber containing the water heated until vaporization. By increasing the weight of the piece covering the valve, the pressure is raised allowing the equilibrium vapor–liquid to be established at higher boiling temperature. Through this procedure, Clausius–Clapeyron equation can be verified and Δ_vapH of water can be estimated. Additionally, a condition (a determined weight) can be selected where the pressure reaches 202 kPa with a boiling temperature of 121 °C. Thus, an ordinary pressure cooker works as an autoclave and a complete sterilization cycle can be performed analyzing each step thermodynamically. Moreover, basic related concepts such as gases features and possible ways of expressing pressure can be discussed by the instructors upon development of the lab exercise. This activity provides a useful tool to enrich a core concept, usually given as a lecture, with an experiment directly connected to real-life and biomedical applications.