Based on the data reported by Rossini et al. (9) analytical expressions have been developed for the calculation of enthalpies at zero pressure as functions of temperature for normal paraffins ranging from methane through octane. The coefficients of these equations have been found to correlate linearly with molecular weight, thus allowing the enthalpy relationships for hydrocarbons heavier than octane to be determined by extrapolation. The enthalpy of mixtures at zero pressure can then be obtained by combining the enthalpies of the individual components on an additive basis, weighted by the mole fractions

Corrections due to nonideal gaseous behavior have been developed in equation form from the work of Lydersen, Greenkorn, and Hougen (7) in terms of the reduced temperature TR and the critical compressibility factor zc of the substance. These corrections have been developed for both the saturated vapor and saturated liquid states and can be applied to the determination of the enthalpy of mixtures at these conditions. The results of this method have been compared with the experimental enthalpy data available for three ternary mixtures and were found to be in excellent agreement.