New Methods for Estimating the Heats of Formation, Heat Capacities, and Entropies of Liquids and Gases

Using group additivity values to estimate ΔvapH°(298) and the Kistiakowsky equation to estimate both ΔvapS°(Tb) and ΔvapH°(Tb) at the boiling point (Tb), it is shown how an average value of ΔvapCp° can be obtained which can then be used to calculate values of ΔvapS°(298). This latter can then be used in conjunction with S°(g,298) to calculate S°(l,298). Alternatively, where values of S°(l,298) are available but not S°(g,298) the latter can be calculated. The method applies to regular liquids, even those with relatively large dipoles but not to H-bonded liquids. The accuracy of estimated values of S°(l,298) are 0.45 ± 0.16 cal/(mol K) with a maximum deviation of 1.0 cal/(mol K) for an assortment of 14 selected compounds and 0.3 ± 0.12 for another 17 liquids for which groups are not available but ΔvapH°(298) and ΔvapS°(298) are. Here the largest deviation is 1.9 cal/(mol K). Calculated values of Cp°(l,298) are much less accurate, ±3 cal/(mol K) with a maximum deviation of 9.0 cal/(mol K). It is also shown t...