Thermodynamic properties of the KCl+H2O system

The thermodynamic properties of the KCl+H2O system were examined in order t o provide: (1) an improved equation for the osmotic coefficient as a functi on of molality and temperature for purposes of isopiestic measurements, (2) a determination of the thermodynamic properties of the standard-state solu tion process, and (3) a test of the accuracy of the enthalpy of solution va lues for KCl(cr), a calorimetric standard. New equations that describe the thermodynamic properties of the KCl+H2O system were obtained from previousl y published measurements for this system. The measured values included in t he fitted equations spanned the range of temperature from approximately 260 to 420 K for KCl(aq) and 1.5 K to 1033.7 K for KCl(cr). New equations and/ or values for the following properties are given in the present work: (1) t hermal properties of KCl(cr) from 0 K to the melting point, 1045 K, (2) the change in chemical potential for both KCI and H2O in KCl(aq) as a function of temperature, and molality, valid from 260 to 420 K, and (3) standard-st ate properties for the aqueous solution process. The effect of heat treatme nt on the determination of enthalpy of solution values was also examined. T his examination indicated that the MST recommendation of heating Standard R eference Material 1655, potassium chloride, at 800 K for a minimum of 4 h p rior to its use in calorimeter calibration, should probably not be followed . The heat treatment recommended by the NIST certificate appears, at this p oint, to have a higher probability of corrupting the sample than improving the accuracy of the measurement. (C) 1999 American Institute of Physics and American Chemical Society. [S0047-2689(99)00101-4].