A property of solutions of equations simulating certain chemical reactions about

We consider the effect of vanishing on an open subset of the domain of a non-trivial solution of a nonlinear equation of "reaction-diffusion" type. Such problem can simulate some of the chemical reactions that occur in the body of the grain of permeable catalyst. We obtain estimates of the size of that part of the domain in which the solution can be non-zero in terms of the distance from the point to the boundary. Explicit formulas for the constants involved in the estimations are given. The results may be useful in the construction of a numerical algorithm for solving the problem.