Carbon Dioxide. The Heat Capacity and Vapor Pressure of the Solid. The Heat of Sublimation. Thermodynamic and Spectroscopic Values of the Entropy

An apparatus for low temperature calorimetric and vapor pressure measurements on condensed gases is described. The heat capacity of solid carbon dioxide has been measured from 15 to 195°K. The heat of vaporization at the sublimation point, 194.67°K, was found to be 6030 cal./mole. The vapor pressure has been measured and the observations are closely represented by the equation: Solid carbon dioxide, 154 — 196°K; log10 P(int. cm Hg) = — (1354.210/T)+8.69903+0.0015880T—4.5107×10—6T2. The entropy of carbon dioxide gas has been calculated from the calorimetric data and the third law of thermodynamics to be 51.11 cal./deg. per mole at 298.1°K. This value is in excellent agreement with the value 51.07 cal./deg. per mole obtained from band spectrum data.