In the conventional theory of complex reactions, overall reactions (ORs) are required to be determined in the first step to specify the stoichiometric matrix. In the present paper, a systematic and straightforward method is proposed for deriving reaction routes (RRs), ORs, and the basic RRs based on the theory of complex reactions. The intermediates are rearranged in a matrix herein named "the matrix of intermediates" which facilitates the combination of elementary reactions building the ORs, distinctively when the number of elementary reactions exceeds. The computer program developed in FORTRAN programming language could execute our suggested methodology automatically. A simple mathematical procedure is further introduced for obtaining explicit overall rate expressions of reactants/products molecules involved in various elementary reactions. The mechanism of n-butane catalytic cracking (CC) over HZSM-5 catalyst has been illustrated as a typical catalytic heterogeneous reaction due to its increasing significance. Both the utilization of the introduced methodology and the theory of complex reactions have been employed for the first time to investigate CC of n-butane over zeolites. (C) 2013 Elsevier Ltd. All rights reserved.