Thermodynamics of aqueous uranyl ion: Apparent and partial molar heat capacities and volumes of aqueous uranyl perchlorate from 10 to 55°C

Abstract

Apparent molar heat capacities and volumes of aqueous solutions containing UO2(ClO4)2 in dilute (≈0.06 molal) HClO4 have been determined from 10 to 55°C. These results have been analyzed using Young's rule to obtain apparent molar volumes and heat capacities for the solute UO2(ClO42). The temperature dependences of the conventional standard-state heat capacity and volume functions for UO22+ (aq) are well represented by the following equations: V̄°/cm(30 mo1P-1) −80.94 + 0.6091 T - 0.001063T2 andC̄/p0/(J K−1 mol−1) = 350.5 — 0.8722T — 5308/T —90) that are valid from 10 to 55°C. These results differ substantially from results of earlier measurements employing different uranyl salts. These differences are likely due to the presence of ion-paired or hydrolyzed U (VI) species in the earlier studies.