| Abstract
| - Various highly accurate ab initio composite methods of Gaussian-n (G1, G2, G3), their variations (G2(MP2), G3(MP2), G3//B3LYP, G3(MP2)//B3LYP), and complete basis set (CBS-Q, CBS-Q//B3LYP) seriesof models were applied to compute reaction enthalpies of the ground-state reaction of CO2 with Mg. Allmodel chemistries predict highly endothermic reactions, with ΔH298 = 63.6−69.7 kcal mol-1. The differencebetween the calculated reaction enthalpies and the experimental value, evaluated with recommendedexperimental standard enthalpies of formation for products and reactants, is more than 20 kcal mol-1 for allmethods. This difference originates in the incorrect experimental enthalpy of formation of gaseous MgOgiven in thermochemical databases. When the theoretical formation enthalpy for MgO calculated by aparticular method is used, the deviation is reduced to 1.3 kcal mol-1. The performance of the methodologiesused to calculate the heat of this particular reaction and the enthalpy of formation of MgO are discussed.
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