Cracking of n-heptane in HZSM-5 zeolite is studied through generalized gradient approximation mediated single point calculations at the BLYP-DZVP level on the extremal points of a corresponding quantum molecular dynamics simulation carried out at 800 K using the same level of theory. The global reactivity descriptors like electronegativity, hardness and electrophilicity are important in understanding the reaction mechanism in terms of the stabilities and reactivities of various species involved. Different centers become reactive towards electrophilic and nucleophilic attacks during the process of hydrocarbon cleavage and local reactivity descriptors adequately take care of that. © 2005 Elsevier B.V. All rights reserved.