Self-consistent density functional calculations for the adsorption of O and CO on flat and stepped Au(111) surfaces are used to investigate effects which may increase the reactivity of Au. We find that the adsorption energy does not depend on the number of Au layers if there are more than two layers. Steps are found to bind considerably stronger than the (111) terraces, and an expansive strain has the same effect. On this basis we suggest that the unusually large catalytic activity of highly-dispersed Au particles may in part be due to high step densities on the small particles and/or strain effects due to the mismatch at the Au-support interface.