An adiabatic calorimeter was used to measure enthalpies of solution into water of sodium chloride (similar to0.13 mol(.)kg(-1)) at nominal temperatures of 298.15 K, 303.15 K, and 308.15 K and of potassium sulfate (similar to0.039 mol(.)kg(-1)) at nominal temperatures of 298.15 K and 303.15 K. The results for sodium chloride were compared to a previous equation of state so as to validate the use of values from that equation of state for calibration of, or checks on the accuracy of, solution calorimeters. Thermodynamic properties from the literature for the potassium sulfate + water system and the present measurements were used to generate equations that represented the thermodynamic properties of this system from the freezing point of the aqueous solution to 500 K. The measured values included in the fitted equations spanned the range of temperature of approximately 271 K to 530 K for K2SO4(aq) and 13 K to 854 K for K2SO4(cr). New equations and/or values for the following properties are given in the present work: (1) thermal properties of K2SO4(cr) from 0 K to near the orthorhombic to hexagonal transition at 857 K, (2) the change in chemical potential for both K2SO4 and H2O in K2SO4(aq) as a function of temperature and molality, valid from 271 K to 500 K, from 0 mol(.)kg(-1) to the saturation molality, and to pressures of 40 MPa, and (3) standard-state properties for the aqueous solution process.