A semi-analytical method has been used to calculate the isothermal effectiveness factor q in a particle for a general kinetic expression of the power law type with external mass transport resistance. Taking this expression for q, it has been shown that it is possible to develop an approximate analytical description of ignition/extinction where reaction is of mth order. The results thus obtained are in reasonable agreement with those derived from numerical integration of the heat and mass balance equations for a spherical, nonisothermal particle. Based on this description, it is possible to use experimentally determined ignition conditions or observed kinetic data, together with the data on pore structure to derive the rate coefficients, provided that the reaction is controlled by a combination of pore diffusion and chemical kinetics. Such an investigation was performed using petroleum coke as a model. The instrinsic rates pi are given from apparent data, by: p,=2300exp( -164/(RT)); and from ignition: pi= 1237exp( -158/(RT)). The kinetic parameters, and the rate expression are in good agreement with the values obtained with the same material by independent methods in other laboratories.