Enthalpies of solution for VOSO4·2.76H2O(s) in water and in aqueous H2SO4

The molal enthalpies of solution of VOSO4·2.76H2O(s) with various molalities in water and in aqueous sulfuric acid (0.5 mol·kg-1), δmHm, were measured by a solution-reaction isoperibol calorimeter at 298.15 K. The value of -δsHm in aqueous sulfuric acid was lower than that in water, which shows that energy state of VOSO4 in aqueous H2SO4 was higher than that in pure water. An improved Archer's method was put forward in terms of ionic association equilibrium of VOSO4 and second dissociation equilibrium of H2SO4. Using the improved method, the standard molal enthalpies of solution δsHm Θ=-29.18 kJ·mol-1 in pure water and δsHm Θ=-25.79 kJ·mol-1 in aqueous sulfuric acid were obtained, respectively. According to calculation, the molality of VO2+ was larger in VOSO4-H2SO4 mixed solution than that in water.