We investigate the roughening of the reaction front in a monomer-monomer surface reaction and determine its fractal dimension. The poisoning kinetics are also investigated. We find that the roughness of the interface obeys a power law, sigma similar to t(beta), and that the reaction rate also obeys a power law, R similar to t(alpha-1). We conjecture that the relation alpha=2 beta holds for these exponents and find this conjecture is very well supported by our simulation results.