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),ΔsHm,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 △s ⊙Hm=-29.18 kJ·mol^-1 in pure water and △s Hm=-25.79 kJ·mol^-1 in aqueous sulfuric acid were obtained,respectively.According to calculation,the molality of VO^2+ was larger in VOSO4-H2SO4 mixed solution than that in water.
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