Thermodynamic Properties of Thionyl Fluoride from 13deg;K to Its Boiling Point. Entropy from Molecular and Spectroscopic Data

摘要

The heat capacity of thionyl fluoride has been measured from 12deg; to 230deg;K for a sample of 99.976 mole purity as determined by the meltinghyphen;point method. The heat of fusion was 1505.9 cal/mole at the solidmdash;liquidmdash;vapor equilibrium temperature of 143.25deg;K. The heat of vaporization at the normal boiling point of 228.84deg;K was 5091 cal/mole. The vapor pressure of the liquid to the normal boiling point has been measured, and the data are represented bylog10Pmmequals;24.41879ndash;1719.074sol;Tminus;5.94452thinsp;log10Twhich was obtained by minimizing the square of the residuals of the pressure.The density of the liquid is represented byd(g/cc)=2.389ndash;0.003398T.The entropy of thionyl fluoride gas in the standard state at the normal boiling point calculated from the experimental data is 63.56 cal/(molemiddot;deg;K). A spectroscopic entropy of 63.28 cal/(molemiddot;deg;K) is calculated from the product of the moments of inertia,IAIBIC=1.6562times;10minus;114g3middot;cm6from microwave data and the following frequency assignment:v1(aprime;)=1336 cmminus;1;v2(aprime;)=808 cmminus;1;v3(aprime;)=530 cmminus;1;v4(aprime;)=378 cmminus;1;v5(aPrime;)=748 cmminus;1; andv6(aPrime;)=396 cmminus;1. The discrepancy between the two entropies is accountable in terms of the experimental uncertainty and therefore, the molecular parameters and frequency assignment are confirmed.