The previously reported dependence of the dissociative sticking probability of oxygen on the Ag(110) surface has been modeled as a random walk between selective adsorption and desorption sites on the surface. Chemisorbed oxygen molecules are allowed to move on an anisotropic surface between boundaries representing the Ag-O added rows and surface steps. Molecules that encounter the added rows are forced to desorb from the surface, while molecules reaching a step react, forming Ag-O units, and become permanently bound. Although simple, the model describes the form and magnitude of the sticking probability as a function of the surface atomic oxygen coverage with only limited and physically reasonable fitting parameters.