Surface molecular dynamics sensitive to reaction sites is now becoming better understood. Spatial and velocity distributions of desorbing products can yield the symmetry and the orientation of the reaction site when the products are repulsively desorbed. These distributions provide an approach by which previously inaccessible dynamics of surface elementary processes on individual reaction sites may be studied. The principles behind this approach and the typical experimental results generated are exemplified in the thermal oxidation process of carbon monoxide on platinum metals. This elementary process takes place mostly at oxygen adsorption sites on flat terraces and is observed on steps only under limited conditions.