Heats of Reaction from Hartree—Fock Energies of Closed-Shell Molecules

If correlation energy were conserved in chemical reactions having only closed‐shell reactants and products, then molecular Hartree—Fock energies could be employed to compute standard heats of reaction. This possibility is here explored by the computation of theoretical heats of reaction for all gas‐phase reactions of molecules for which Hartree—Fock energies are available. For the formation of two moles of HF, the theoretical and experimental heats of reaction differ by 16 kcal. The sum of the correlation energies of H2 and F2 is apparently greater than in two HF molecules. For five other reactions examined, the theoretical and experimental heats of reaction differed by 11 kcal or less. Conversely, thermochemical data are combined with known Hartree—Fock energies to predict the Hartree—Fock energies of methane, water, and ammonia. It is concluded that the theoretical prediction of standard heats of reaction to an accuracy of 2 kcal/mole will require a semiquantitative prediction of the change in correlati...

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