The standard enthalpy of formation of anhydrous, monohydrated, and dihydrated zirconium bis(monohydrogenphosphate)

Abstract

The enthalpies of solution of amorphous and crystalline Zr(HPO 4) 2 · H 2O, of Zr(HPO 4) 2, and Zr(HPO 4) 2 · 2H 2O have been measured calorimetrically and the standard enthalpies of formation derived. The results obtained are as follows: ΔH f o(s, 298.15 K)/kJ mol −1 Zr(HPO 4) 2 · H 2O(am) −3435.8 ± 4.2 Zr(HPO 4) 2 · H 2O(c) −3463.7 ± 4.1 Zr(HPO 4) 2(c) −3167.9 ± 4.1 Zr(HPO 4) 2 · 2H 2O(c) −3741.2 ± 4.1 In order to establish an unambiguous assessment of the degree of crystallinity of these exchangers, the ΔH o of other Zr(HPO 4) 2 · H 2O samples prepared by different techniques with various conditions have also been determined.