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  Home > JCE Print > Journal of Chemical Education > Issues > 2006  > July  >
In the Classroom
JCE DigiDemos: Tested Demonstrations
A Demonstration of the Continuous Phase (Second-Order) Transition of a Binary Liquid System in the Region around Its Critical Point
Michael R. Johnson
Department of Chemistry, Virginia Polytech Institute and State University, Blacksburg, VA 24061

checked by: Vladimir M. Petrusevski
Institute of Chemistry, Faculty of Natural Sciences and Mathematics, Sts. Cyril and Methodius University, Arhimedova 5, 1000 Skopje, Macedonia

Cover
July 2006
Vol. 83 No. 7
p. 1014
Abstract
In most general chemistry and introductory physical chemistry classes, critical point is defined as that temperature–pressure point on a phase diagram where the liquid–gas interface disappears, a phenomenon that generally occurs at relatively high temperatures or high pressures. Two examples are: water, with a critical point at 647 K (critical temperature: Tc) and 215 bar (critical pressure: Pc); and carbon dioxide, with a critical point of 304 K (Tc) and 73 bar (Pc). In colloid chemistry, there is another critical point, which occurs at a specific temperature and mole fraction in a specific binary liquid system where immiscible or partially miscible species become completely miscible. These phenomena of colloidal systems occur at atmospheric pressure and over a temperature range which, for some systems, includes room temperature (~300 K). The purpose of this demonstration is to show this critical-temperature phase-transition phenomenon for a specific binary liquid system, where Tc is ~300 K.
More Information
*  Citation
 Johnson, Michael R. J. Chem. Educ. 2006 83 1014.
*  Keywords
 Colloids; Demonstrations; Graduate Education / Research; Hands-On Learning / Manipulatives; Liquids; Phases / Phase Transitions / Diagrams; Physical Chemistry; Solutions / Solvents; Thermodynamics; Upper-Division Undergraduate
*  History
 Created:
Last Updated:		 5/26/2006
5/26/2006
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