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  Home > JCE Print > Journal of Chemical Education > Issues > 1998  > July  >
In the Laboratory
The Determination of the Heat Capacities of Liquids with Time Resolved Thermal Lens Calorimetry: A More Accurate Procedure
Kurt Seidman and Amy Payne
Randolph-Macon Woman's College, Department of Chemistry, Lynchburg, VA 24503
Cover
July 1998
Vol. 75 No. 7
p. 897
Abstract
The application of thermal lens calorimetry to the determination of the heat capacities of liquids has been reported in the literature. The accuracy is poor; a 60% error was reported for the heat capacity of methanol. This article describes a modified procedure that dramatically improves the accuracy of the method. A set of standard solutions was prepared from solvents of known heat capacity and the dye indophenol blue. The concentration of the dye in each solvent was adjusted to produce a solution with the same absorbance at 632nm, the wavelength of the laser used to perform the studies. These standards were used to produce a calibration line that allows one to systematically adjust the lens to sample distance and the size of the aperture in the diaphragm through which the laser beam passes. These adjustments are based upon the size of the thermal bloom produced as the laser beam passes through a sample. Standards were prepared from acetone, benzene, carbon tetrachloride, ethanol and methanol at three different absorbances. The calibration lines were used to determine the heat capacities of chloroform and toluene at each absorbance. The average relative errors for the heat capacities of chloroform and toluene were 3.0% and 2.6%, respectively.
More Information
*  Citation
 Seidman, Kurt; Payne, Amy. J. Chem. Educ. 1998 75 897.
*  Keywords
 Laboratory Instruction, Physical Chemistry, Calorimetry, Laser Spectroscopy, Thermodynamics
*  History
 Created:
Last Updated:		 June 22, 1999
June 24, 2005
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