APPARENT MOLAR HEAT-CAPACITIES AND VOLUMES OF LACL3(AQ), LA(CLO4)(3)(AQ), AND GD(CLO4)(3)(AQ) BETWEEN THE TEMPERATURES 283 K AND 338 K

The apparent molar heal capacities and volumes of LaCl3(aq), La(ClO4)( 3)(aq), and Gd(ClO4)(3)(aq) have been measured at the temperatures (28 3, 298, 313, 328 and 338) K and molalities from about 0.05 mol . kg(-1 ) to 0.7 mol . kg(-1) in a Picker flow microcalorimeter and a vibratin g tube densitometer. The results were analyzed by means of the Fitter equations to derive standard partial molar heat capacities and volumes and expressions for the excess properties. The revised Helgeson-Kirkh am-Flowers (HKF) model has been found to represent the temperature dep endence of the standard partial molar properties within the experiment al uncertainty. A modification to the non-electrostatic heat capacity function in the HKF model yields an improved fit to the experimental r esults for La(ClO4)(3) and Gd(ClO4)(3). (C) 1996 Academic Press Limite d