The standard molar enthalpies of formation of UTeO5 and UTe3O9

The molar enthalpies of solution of UTeO5, UTe3O9, TeO2, and UO3 in HCl (aq , c = 11 mol . dm(-3)) have been measured by using an isoperibol calorimete r From these results and other auxiliary data, the standard molar enthalpie s of formation Delta(f)H(m)(o)(298.15 K) of UTeO5(cr) and UTe3O9(cr) have b een calculated to be -(1606.3 +/- 3.5) kJ . mol(-1) and -(2287.2 +/- 9.5) k J . mol(-1), respectively. These values of enthalpies of formation of UTeO5 and UTe3O9 are consistent with the second-law enthalpies of formation of t hese compounds derived from their vapour pressures determined in this labor atory by a transpiration technique. (C) 1999 Academic Press.