While the molecular fragment reference basis sets still conserve the stoichiometry, they also conserve the bond types in the molecule, which leads to differences between the reference fragments in the products and reactants. Consequently, these approaches do not necessarily conserve the surface reaction enthalpies of a mechanism at the DFT values. Instead, they conserve surface reaction enthalpies of alternative reactions that maximize error cancellation for a given electronic structure method . Fig. shows the enthalpy diagram with ∆ f H from experiments, ATcT, and the isodesmic reactions. Since the enthalpies of the gas-phase species are directly from the ATcT, we match the reaction enthalpy exactly, which is identical to the adsorption reaction approach in Section 4.3.2. The DFT energy of the empty slab is also no longer needed. The reaction enthalpies now vary considerably in comparison to the previous methods. The dissociation of ethane to ethyl changed from endothermic to exothermic and the subsequent dissociation step is even more exothermic. Furthermore, the formation of *OH is also exother- mic, while the endothermicity for the dissociation of CO * 2 increased significantly. Assuming the experimentally measured adsorption enthalpies are more accurate than DFT, it follows that the free energy pathway constructed from the CBH expansion approach should also be more accurate. However, it is only possible to calculate ∆ f H using the CBH approach in cases where the experimental (or other highly accurate) reaction enthalpies of the requisite reference species are known.