Enthalpy of dissolution of the complex Zn(Leu)SO₄·l/2H₂O (s)

Abstract

Molar enthalpies of dissolution of [ZnSO₄·7H₂O (s) and Leu(s)] mixture [<i>n</i> (ZnSO₄·7H₂O) : <i>n</i> (Leu) = 1 : 1] and the complex Zn(Leu)SO₄·l/2H₂O (s) in 100 cm^-3 of 2 mol·dm^-3 HCl at (298.15 ± 0.001) K have been determined to be Δ_d<i>H</i>^o_m.1 = -(84.943 ± 0.090) kJ-mol^-1 and Δ_d<i>H</i>^o_m.3 = (55.967 ± 0.060) kJ-mol^-1, respectively, using an isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the complex Zn(Leu)SO₄·l/2H₂O (s) has been found to be Δ_f<i>H</i>⁰_m Zn(Leu)SO₄·l/2H₂O ,s, 298.15 K) =-(1998.155 ± 0.965) J·mol^-1, on the basis of experimental values of enthalpies of dissolution with some auxiliary thermodynamic data through a designed Hess thermochemical cycle. The constant-volume combustion energy of the complex Zn(Leu)SO₄·l/2H₂O (s) has been measured to be

Δc<i>E / </i>J.g^-1 = -(9971.85 ± 11.27) by a precision rotating bomb combustion calorimeter at 298.15 K. The standard molar enthalpy of combustion and formation of the compound have been calculated to be Δ_c<i>H</i>⁰_m =-(3007.889 ± 3.399) kJ.mol^-1 and Δ_f<i>H</i>⁰_m Zn(Leu)SO₄·l/2H₂O (s)=-(2001.251 ± 3.503) J·mol^-1. The relative deviation of results obtained from the two calorimetric methods agree with each other and is within ± 0.2%.