This report describes a combined experimental and theoretical approach to the problem of designing surface alloys with specific chemical properties. Au-Ni(111) surface alloys were prepared and the distribution of active sites was determined by atomically resolved STM as a function of Au coverage. Using density functional theory the difference in activation energy for methane over the various sites was determined. The activity of the surface could be predicted directly by combining this information with the distribution of sites. Subsequent measurements of the activity proved this method to be quantitative and demonstrated that surface alloys with specific activity can be synthesized.