The thermochemical data for the ideal gases of this appendix are taken directly from the Third Edition of the JANAF Thermochemical Tables, as tabulated by Chase et al. (1985). The twelve atoms and molecules selected are frequently cited in papers dealing with the chemistry and physics of flames and plasmas. For the sake of brevity, the plethora of possible hydrocarbons are not included in this appendix, but many of them can, of course, be found in the complete JANAF tables, which are available in the reference section of most science and engineering libraries.

The ordered listing of the twelve chosen gases is as follows: H ₂, H, O ₂, O, H ₂O, OH, CO, CO ₂, N ₂, N, NO, and NO ₂. Each table describes the formation of one mole of the subject species from its elements in their natural physical state at 298.15 K and 1 bar. The reader should refer to the original JANAF tables for a listing of the quantum mechanical and spectroscopic data used to effect the statistical mechanical calculations for each species. The reference state for all of these compounds is the hypothetical ideal gas at a temperature of 298.15 K ( T _r) and a pressure of 1 bar (0.1 MPa). The logarithm of the equilibrium constant is to the base 10. By definition, both the enthalpy and Gibbs free energy of formation are identically zero for any ideal gas reference compound, such as H