Catalytic cracking and steam cracking are two processes used to break down long-chain hydrocarbons. Describe both processes and explain why cracking is important to the petrochemical industry.

Catalytic cracking involves heating long‑chain hydrocarbons until they vapourise, then passing the vapour over a hot powdered aluminium oxide catalyst, which breaks the C–C bonds to give smaller alkanes and alkenes. Steam cracking mixes the hydrocarbon vapour with steam and heats it to a very high temperature, causing thermal cleavage of the chains to produce mainly alkenes and short‑chain alkanes. Cracking is important because the smaller molecules are useful as fuels and, especially the alkenes, serve as key feedstocks for the petrochemical industry to manufacture polymers and other chemicals.