Ethalpies of Solution of Sodium Chloride and Potassium Sulfate in Water. Thermodynamic Properties of the Potassium sulfate + Water System

摘要

An adiabatic calorimeter was used to measure enthalpies of solution into water of sodium chloride (approx 0.13 mol kg~(-1) at nominal temperatures of 298.15K, 303.15K, and 308.15K and of potassium sulfate (approx 0.039 mol kg~(-1))at nominal temperatures of 298.15K and 303.15K. The results for sodium chloride were compared to aprevious equation of the state so as to validate the use of values from that equatiohn 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 K_2SO_4(aq) and 13 K to 854K for K_2SO_4(cr). New equations and/or values for the following properties are given in the present work: (1) thermal properties of K_2SO_4 (cr) from 0k to near the orthorhombic to hexagonal transition at 857 K, (2) the change in chemical potential for both K_2SO_4 and H_2O in K_2SO_4 (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 pressure of 40 MPa, and (3) standard-state properties for the aqueous solution process.