Thermodynamic Properties of Aqueous (NH4)2SC4 to High Supersaturation as a Function of Temperature

Equilibrium water vapor pressures over supersaturated aqueous ammonium sulfate have been determined from 278.15 to 313.15 K using an electrodynamic balance. Partial molar enthalpies of water (L1, to ~25 mol kg-1) and partial molar heat capacities (J1, to ~8 mol kg-1) have been calculated from the measurements, together with enthalpies of solution, heat capacities, and boiling point elevations. The results have been used to parameterize a mole-fraction-based activity coefficient model. Equilibrium constants for the reaction (NH4)2SO4(cr) ⇄ 2NH4+(aq) + SO42-(aq) have been evaluated from 373.15 K to the eutectic point (5.00 mol kg-1, 254.21 K). The model satisfactorily represents water vapor pressures and saturation with respect to solid phases ice and ammonium sulfate from 253 to > 373.15 K and up to 8-10 mol kg-1, and water vapor pressures from 278.15 to 313.15 K and up to ~25 mol kg-1. © 1995, American Chemical Society. All rights reserved.