Dissolution of potassium chloride as a test process for isothermal calorimeters operated in the milli-Watt range

Abstract

A test and calibration method for isothermal calorimeters equipped with a device for liquid injection and mixing is described. The procedure was developed with special reference to calorimeters operated with heat flow values in the milli-watt range. The investigated reaction was the dissolution of potassium chloride in water at 298 K in the concentration range 56–80 water molecules per KCl entity or molalities of 0.7−1 mol kg−1. The solution enthalpies (ΔsolH) were assessed after electrical calibration and correction for side effects obtained from separate blank measurements. The obtained values were corrected to the state of infinite dilution (ΔsolH∞) at each experimental molality by use of literature values of the relative apparent enthalpy of dilution. The obtained result was 229.6 ± 1.0 J g−1 (n = 16). The solution enthalpy (ΔsolH) as a function of molality in the experimental concentration interval was fitted by a 1-order polynomial resulting in a slope of -12.3 J g−1 mol−1 kg and intercept of 240.5 J g−1. The results are suggested as reference values for validation of calorimeters calibrated electrically or for the purpose of calibration.