H₂O-NH₄Cl system: Is there a thermodynamic response to the nucleation point?

Abstract

According to literature data (J. Phys. Chem. A, 115, 3393–3460 (2011)), NH₄Cl concentrations in nanoobjects such as aerosol droplets can be as high as 28m, which corresponds to a 60 % solution (nucleation concentration). At this concentration, the heat of dissolution of the salt is shown to be temperature independent (the heat capacity of dissolution is zero). This means that the entropy of dissolution is also temperature independent. Relative partial enthalpies are determined for the components of the H₂O-NH₄Cl system over the entire range of compositions at 248–373 K. The excess enthalpy of the 60 % solution has extreme values of 810 J/mol, 261 J/mol, −184 J/mol, and −553 J/mol at 273 K, 298 K, 323 K, and 348 K, respectively. At 312 K, H ^E ≈ 0. At 298 K, the excess heat capacity and volume show negative nonidealities with a minimum at 60 % for C ^E _P (−19.7 J/(mol·K)) and 57% for V ^E (−0.44 cm³/mol). The composition dependence of the specific heat capacity (in relation to a unit of weight) has a minimum at an equimolar salt:water ratio.