Paper detail

Low-temperature data for carbon dioxide

We investigate the empirical data for the vapor pressure (154$ \leq$$T$$\leq$196 K) and heat capacity (15.52$ \leq$$T$$\leq$189.78 K) of the solid carbon dioxide. The approach is both theoretical and numerical, using a computer algebra system (CAS). From the latter point of view, we have adopted a cubic piecewise polynomial representation for the heat capacity and reached an excellent agreement between the available empirical data and the evaluated one. Furthermore, we have obtained values for the vapor pressure and heat of sublimation at temperatures below 195 right down to 0 K. The key prerequisites are the: 1) Determination of the heat of sublimation of 26250 J$\cdot$mol\textsuperscript{-1} at vanishing temperature and 2) Elaboration of a `linearized' vapor pressure equation that includes all the relevant properties of the gaseous and solid phases. It is shown that: 1) The empirical vapor pressure equation derived by Giauque & Egan remains valid below the assumed lower limit of 154 K (similar argument holds for Antoine's equation), 2) The heat of sublimation reaches its maximum value of 27211 J$\cdot$mol\textsuperscript{-1} at 58.829 K and 3) The vapor behaves as a (polyatomic) ideal gas for temperatures below 150 K.