Cracking is the process by which longer chain hydrocarbons are split into shorter, more useful hydrocarbons.

Generally, cracking results in an alkane and an alkene.

Cracking produces shorter-chain hydrocarbons. These products are useful because:

1. They can be used as chemical feedstocks for the petrochemical industry.
2. They make more efficient fuels (than longer-chain hydrocarbons).

Thermal decomposition

Thermal decomposition involves the breaking down of molecules using heat.

Thermal cracking and catalytic cracking.

Thermal cracking uses very high temperatures (≈1,000°C) and high pressures (up to 70 atm).

Catalytic cracking uses lower temperature (≈450°C), lower pressure, and a zeolite catalyst.

Thermal cracking mainly produces alkenes.

Catalytic cracking mainly produces aromatic hydrocarbons.

1. Long chain alkanes are heated to very high temperatures (around 1,000°C) under high pressure (about 70 atm).
2. At these extreme conditions, the long chain alkanes break into smaller fragments.
3. The fragments recombine to form a mixture of shorter chain alkanes and alkenes.

Cracking is economically important because it converts less valuable, longer chain hydrocarbons into more valuable, shorter chain hydrocarbons. These products, such as alkenes and aromatic compounds, are essential chemical feedstocks for the petrochemical industry and are in high demand for manufacturing plastics, chemicals, and fuels.

1. Long chain alkanes are heated until they vaporise into a gas.
2. The gaseous alkanes are passed over a zeolite catalyst (hydrated aluminosilicate) at around 450°C.
3. This breaks the long chain alkanes into a shorter chain alkane and an alkene.

The products of cracking are an alkene and an alkane.

For example, decane can be cracked to give ethene and octane: C₁₀H₂₂ ➔ C₂H₄ + C₈H₁₈.