The cracking reaction pathways and mechanisms of n-hexadecane with a rare earth Y (REY) catalyst were studied. Experiments at 500 degrees C indicated that the dominant reactions were isomerization and cracking to smaller paraffins and olefins. These results were described in terms of a kinetic model that was based on a novel mechanism-oriented lumping scheme that exploits the chemical similarities within reaction families of elementary steps. Thus, 13 reaction family matrices were able to describe all of the elementary steps. Formal application of these reaction matrices to the matrix representations of the reactants and derived products generated the model. The reaction family concept was further exploited to constrain the kinetics within each reaction family to follow a quantitative structure/reactivity Polanyi relationship. Ultimately, three Polanyi, relationship parameters, one catalyst-specific parameter and two coking/deactivation parameters, were determined by optimizing the model fit to the experimental data. The resulting model correlations were excellent, which suggests the optimized parameters contain fundamental structure/reactivity information.