“…As the diffusion-reaction equations describing the system are nonlinear, it is difficult to solve them and their general solutions remain unknown (except of very special cases). Thus, to simplify the calculations one usually uses various approximations, such as the quasistationary approximation [1,2,3], the scaling method [1,4,5,6,7], or the perturbation one [9,10]. Using these methods, there were derived characteristic functions of the system which include: the time evolution of the reaction front x f (t), the width of the reaction zone W R (t) or the width of the depletion zone W Dep (t) [1,2,4,5,6] which all appear to be the power functions of time f (t) = Kt γ .…”