A Gibbs free energy equation of state (EoS) for phase I of solid methane has been developed with an original functional form. The EoS has a validity range from 21 to 300 K and up to 5000 MPa. The EoS parameters have been regressed on the literature data of molar volume, isothermal compressibility, thermal expansion, and isobaric and isochoric heat capacity. To the knowledge of the authors, this EoS is the most complete published model for phase I of solid methane in terms of the number of data of different thermodynamic properties used for the regression of the parameters and extension of the temperature and pressure validity range. The EoS represents the thermodynamic data within their estimated experimental uncertainty, and it maintains a physically correct behavior when extrapolated to high temperatures and pressures. The developed EoS for solid methane has been coupled with the reference equation of state for the fluid phases developed by Setzmann and Wagner in 1991 for calculating the melting and sublimation curves, and the predictions are in good agreement with the available data.

The functional form developed in Stringari Stringari J. Chem. Eng. Data20216611571171 has been applied for obtaining a Gibbs free energy equation of state (EoS) for phase I of solid benzene. The EoS has a validity range from 15 K up to the temperature and pressure of the solid II–solid I–liquid triple point, that is, 488.3 K and 1164.6 MPa. The EoS parameters have been regressed on literature data of molar volume, isothermal compressibility, thermal expansion, and isobaric and isochoric heat capacities. The average absolute deviation between the EoS and the primary data is 6.8% for isothermal compressibility, 5.5% for isobaric thermal expansion, 0.9% for molar volume, 2.7% for isobaric heat capacity, and 4.9% for isochoric heat capacity. The EoS maintains a physically correct behavior in the whole range of temperature and pressure of existence of phase I of solid benzene. The developed EoS for solid benzene has been coupled with the reference equation of state for the fluid phases developed by Thol Thol High Temp.-High Press2012418197 for calculating the melting and sublimation curves. Predictions of sublimation pressures are in excellent agreement with the recommended values of Ružička Ružička J. Chem. Thermodynamics2014684047 and those of melting temperatures matches very well the values obtained from the auxiliary melting equation in the validity limits of the EoS of Thol Thol High Temp.-High Press2012418197.

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