Temperature Dependent Thermodynamic Model of the System H+−NH4+−Na+−SO42−−NO3−−Cl−−H2O

Abstract

A thermodynamic model of the system H(+)-NH₄(+)-Na(+)-SO₄²⁻-NO₃⁻-Cl⁻-H₂O is parametrized and used to represent activity coefficients, equilibrium partial pressures of H₂O, HNO₃, HCl, H₂SO₄, and NH₃, and saturation with respect to 26 solid phases (NaCl(s), NaCl·2H₂O(s), Na₂SO₄(s), Na₂SO₄·10H₂O(s), NaNO₃·Na₂SO₄·H₂O(s), Na₃H(SO₄)₂(s), NaHSO₄(s), NaHSO₄·H₂O(s), NaNH₄SO₄·2H₂O(s), NaNO₃(s), NH₄Cl(s), NH₄NO₃(s), (NH₄)₂SO₄(s), (NH₄)₃H(SO₄)₂(s), NH₄HSO₄(s), (NH₄)₂SO₄·2NH₄NO₃(s), (NH₄)₂SO₄·3NH₄NO₃(s), H₂SO₄·H₂O(s), H₂SO₄·2H₂O(s), H₂SO₄·3H₂O(s), H₂SO₄·4H₂O(s), H₂SO₄·6.5H₂O(s), HNO₃·H₂O(s), HNO₃·2H₂O(s), HNO₃·3H₂O(s), and HCl·3H₂O(s)). The enthalpy of formation of the complex salts NaNH₄SO₄·2H₂O(s) and Na₂SO₄·NaNO₃·H₂O(s) is calculated. The model is valid for temperatures < or approximately 263.15 up to 330 K and concentrations from infinite dilution to saturation with respect to the solid phases. For H₂SO₄-H₂O solutions the degree of dissociation of the HSO₄⁻ ion is represented near the experimental uncertainty over wide temperature and concentration ranges. The parametrization of the model for the subsystems H(+)-NH₄(+)-NO₃⁻-SO₄²⁻-H₂O and H(+)-NO₃⁻-SO₄²⁻-Cl⁻-H₂O relies on previous studies (Clegg, S. L. et al. J. Phys. Chem. A 1998, 102, 2137-2154; Carslaw, K. S. et al. J. Phys. Chem. 1995, 99, 11557-11574), which are only partly adjusted to new data. For these systems the model is applicable to temperatures below 200 K, dependent upon liquid-phase composition, and for the former system also to supersaturated solutions. Values for the model parameters are determined from literature data for the vapor pressure, osmotic coefficient, emf, degree of dissociation of HSO₄⁻, and the dissociation constant of NH₃ as well as measurements of calorimetric properties of aqueous solutions like enthalpy of dilution, enthalpy of solution, enthalpy of mixing, and heat capacity. The high accuracy of the model is demonstrated by comparisons with experimentally determined mean activity coefficients of HCl in HCl-Na₂SO₄-H₂O solutions, solubility measurements for the quaternary systems H(+)-Na(+)-Cl⁻-SO₄²⁻-H₂O, Na(+)-NH₄(+)-Cl⁻-SO₄²⁻-H₂O, and Na(+)-NH₄(+)-NO₃⁻-SO₄²⁻-H₂O as well as vapor pressure measurements of HNO₃, HCl, H₂SO₄, and NH₃.