Hypothetical Thermodynamic Properties: Vapor Pressures and Vaporization Enthalpies of the Even n-Alkanes from C40 to C76 at T ) 298.15 K by Correlation-Gas Chromatography. Are the Vaporization Enthalpies a Linear Function of Carbon Number?

The temperature dependence of gas chromatographic retention times of tetracontane to hexaheptacontane is reported. These data are used in combination with earlier work to evaluate the vaporization enthalpies and vapor pressures of these n-alkanes from T ) (298.15 to 540) K. The vapor pressure and vaporization enthalpy results obtained are compared with data calculated by the program PERT2 and Antoine constants estimated by Kudchadker and Zwolinski. The results are also compared with a model previously developed from empirical data which predicts that vaporization enthalpies measured at the boiling temperatures should approach a maximum value and then asymptotically approach zero as the chain length approaches infinity. Some curvature is indeed observed as the number of carbon atoms exceeds sixty.