Low-Temperature Heat Capacity and Related Thermodynamic Functions of Propylene Oxide

The heat capacity of propylene oxide has been determined from 11° to 300°K in an automatic low-temperature adiabatic calorimeter. The melting point of propylene oxide is 161.22°±0.05°K and the heat of melting is 1561.4±1.7 cal/mole. The absolute entropy at 298.15°K is 46.91±0.15 cal/mole·°K) which includes a residual entropy of R ln 2 for the entropy of mixing of the optical isomers. The third-law entropy of gaseous propylene oxide at 298.15°K is determined from the entropy of the liquid plus literature data on the heat of vaporization, vapor pressure, and the critical constants. This entropy value is in good agreement with the value determined from statistical thermodynamics using literature data on the fundamental vibrational assignment, the internal rotational barrier, and the entropy of mixing.