New methods for estimating the heats of formation, heat capacities, and entropies of liquids and gases

Using group additivity values to estimate Delta(vap)H degrees(298) and the Kistiakowsky equation to estimate both Delta(vap)S degrees(T-b) and Delta(vap)H degrees(T-b) at the boiling point (T-b), it is shown how an average value of Delta(vap)C(p)degrees can be obtained which can then be used to calculate values of Delta(vap)S degrees(298). This latter can then be used in conjunction with S degrees(g,298) to calculate S degrees(l,298). Alternatively, where values of S degrees(l,298) are available but not SO(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 degrees(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 Delta(vap)H degrees(298) and Delta(vap)S degrees(298) are. Here the largest deviation is 1.9 cal/(mol K). Calculated values of C(p)degrees(l,298) are much less accurate, +/-3 cal/(mol K) with a maximum deviation of 9.0 cal/(mol K). It is also shown that the best average value of C(p)degrees to use in calculating changes in Delta H degrees and Delta S degrees in a specified temperature interval, T-1 to T-2, is the arithmetic mean of the initial and final values, [C(p)degrees(T-1) + C(p)degrees(T-2)]/2. Changes are recommended in some of the group values for calculating Delta(vap)H degrees(298) and also in the group O-(C)(2) for calculating gas-phase entropies of ethers and for N-(C)(2)(H) for calculating entropies of secondary amines.