I present a computational study of the reactivity between NH\sb3 and the Ga\sb5As\sb5 cluster. A single NH\sb3 molecule approaches several sites on the cluster and the system is relaxed to its local lowest energy configuration. In this study, gallium sites are found to lead to lower total energies, due to greater contributions to densities of states near the Fermi level. Two ammonia molecule are then allowed to react with the cluster in sequence, each approaching different sites. Interaction at one site is seen to reduce the reactivity at other sites. These results are discussed in light of experimental studies performed on these clusters.