Equation of State for Solid Carbon Dioxide Based on the Gibbs Free Energy

In this work a fundamental equation of state explicit in the Gibbs free energy was established, which was fitted to experimental data (heat capacity, molar volume, expansion coefficient, and compressibility) of solid carbon dioxide. Almost all of the data that the equation was fitted to are represented within the experimental uncertainty given by the authors. However, only very limited data for the thermodynamic properties of solid carbon dioxide are available. The new equation behaves physically reasonably within its range of validity. Sublimation and melting pressures of dry ice are predicted accurately using Gibbs energies calculated from the new dry ice equation and from the fundamental equation by Span and Wagner for the fluid phase (J. Phys. Chem. Data1996, 25, 1509–1596). The results agree with those of the reference equations for sublimation and melting pressure published by Span and Wagner mostly within the uncertainty given for these equations. The resulting sublimation and melting pressures are very sensitive to variations of the Gibbs energy. The use of another equation of state for the fluid phase has a significant impact on the calculated equilibrium pressures. It is shown that the equation for dry ice also might be used for the calculation of equilibria with dry ice in the solid phase and mixtures in the fluid phase.