The Heat Capacities and Entropies of Calcium and Barium Sulfates from 15 to 300deg;K. The Entropy and Free Energy of Sulfate Ion

摘要

The heat capacities of BaSO4and small precipitated crystals of CaSO4sngbnd;2H2O have been measured from 15 to 300deg;K. The heat capacity of large naturally occurring gypsum crystals was measured from 60 to 274deg;K. TheCpagainst logTplots of the molal heat capacities of the two samples of CaSO4sngbnd;2H2O differing in crystal surface by a factor of roughly 106show slight deviations from each other. We believe these variations to be outside the limits of experimental error. However, they do not produce a change in entropy at 298.1deg;K. Sdeg;298.1of CaSO4sngbnd;2H2O and BaSO4were determined to be 46.36 and 31.51 E.U. respectively with an accuracy of 0.05 percent. The final value of Sdeg;298.1of SO4mdash;mdash;from this series of measurements is 3.5 E.U. The free energy of formation of SO4mdash;mdash;has been calculated as mdash; 175,300 cal.