Via the formation process of the adsorbed intermediates formyl (HCO) and hydroxy-carbene (COH), the thermodynamics of the hydrogen-assisted CO dissociation on Fe(310) is investigated by means of first-principles total-energy calculations. A comparison with direct CO dissociation in the presence of coadsorbed atomic hydrogen leads to the conclusion that the direct process is the only thermodynamically viable route for CO dissociation on Fe(310), with strongly endothermic formation energies for both intermediates, HCO and COH. (C) 2012 Elsevier B.V. All rights reserved.