Publishing House SB RAS:

Publishing House SB RAS:

Address of the Publishing House SB RAS:
Morskoy pr. 2, 630090 Novosibirsk, Russia



Advanced Search

Journal of Structural Chemistry

2009 year, number 6

CONCENTRATION, TEMPERATURE, AND ISOTOPY EFFECTS ON THE HEAT CAPACITY OF AQUEOUS UREA

V. P. Korolev
Keywords: urea, aqueous solutions, heat capacity
Pages: 1147-1154

Abstract

Relations for the apparent molar heat capacity φс of urea in an aqueous solution depending on the molality m and temperature were obtained. A transition to the relations φс(m,T) for D2O-(ND2)2CO and Т2O-(NТ2)2CO systems was effected by temperature scaling. At low temperatures, the isotherms of the molar heat capacity Cp(m) of the protium and deuterium systems have minima shifted to more dilute solutions at elevated temperatures. At m = 1, Cp of a solution does not depend on temperature in both systems. The dependences Cp(T) also have minima at constant concentrations. The temperature of the minimum heat capacity is most effectively lowered by small additions of urea. For m = 0.25, Tmin is 7.5 K lower than Tmin of pure water, and its heat capacity is 0.08 J/(mol K) higher. A transition from m = 1.5 to m = 2 lowers the temperature of the minimum heat capacity by 3.6 K; thus, the heat capacity of solutions differs by 0.02 J/(mol K) only.