Computational Chemistry Comparison and Benchmark DataBase Release 22 (May 2022) Standard Reference Database 101 National Institute of Standards and Technology
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Species with well-known enthalpies of formation

For example, if we wanted to calculate the enthalpy of formation of CH₃Cl we could use an atomization reaction:
CH₃Cl = C + 3 H + Cl
or we could use an isogyric reaction:
CH₃Cl + H₂O = H₂CO + HCl + H₂
While the experimental uncertainties in the enthalpies of formation of the products are very similar for both reactions, the calculated reaction enthalpy is expected to be closer to experiment for the second, isogyric, reaction.

The following list suggests, for each element, some species with well defined enthalpies of formation.

Enthalpies in kJ mol^-1