Enthalpy of formation of europium dichloride and thermodynamic properties of the +2 and +3 aqueous ions of europium

Abstract

Enthalpies of solution of anhydrous EuCl2 have been measured at 298.15 K in dilute hydrochloric acid solutions which were either oxygen-saturated or oxygen-free. Because of ambiguity in the oxidation of Eu2+(aq) by oxygen, enthalpies of oxidation of Eu2+(aq) have also been measured using bromine water and liquid bromine. Combined with other recent thermochemical measurements, the above experiments yield ΔHof(Eu2+, aq) = −(527.8 ± 5.4) kJ mol−1, ΔHof(Eu3+, aq) = −(604.8 ± 3.8) kJ mol−1, and ΔHof(EuCl2, c) = −(824.4 ± 5.9) kJ mol−1. The Eu(III, II) electrode potential has been measured in dilute chloride solutions, with the recommended result −(0.35 ± 0.03) V. These data have been combined to yield So(Eu2+, aq) = −(10 ± 12) J K−1 mol−1.