Well, this inspired me to review the Wikipedia article on cracking. While we normally think of hydrocarbons as inert, did you know that methane has been protonated to produce CH5(+)? It even has an NMR. If this is true, then how might an acid react with a hydrocarbon (at high temperature)? If there was branching in the feed hydrocarbon, how might that affect the cracking process? How might catalyzed cracking differ from thermal cracking? (No, I don't KNOW anything about cracking. I'm only thinking hypothetically.)