The Eley-Rideal reactions of H atoms with Cl adsorbed on Au(111) surfaces are examined. Electronic structure calculations based on density functional theory are used to construct a model potential energy surface. Both quantum and quasiclassical methods are used to compute reaction cross sections and product state distributions. Steering of the incident H atom towards the adsorbed Cl leads to relatively large reaction cross sections of 2-3 Angstrom(2). The product HCl in this strongly exothermic reaction has over an eV of energy in vibrational motion, and a bit less than one eV each in rotation and translation. (C) 2003 American Institute of Physics.