4.18: Explain Why Cracking is Necessary, in Terms of the Balance Between Supply and Demand for Different Fractions

LONG - CHAIN HYDROCARBONS: Molecule with large number of hydrocarbon molecules

SHORT - CHAIN HYDROCARBONS: Molecule with small number of hydrocarbon molecules

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WHY CRACKING IS NECESSARY:

• Although each fraction obtained from the fractional distillation of crude oil is useful, more long-chain hydrocarbons are produced than needed
• However, less short-chain hydrocarbons are produced than needed (e.g gasoline fraction) as there is a higher demand for short-chain hydrocarbons to be used as polymers for plastic, gasoline, and petrol for cars
• Hence, cracking is necessary to provide for the insufficient supply of short-chain hydrocarbons

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Example: Cracking of Decame ( C10H22 ) to produce Octane ( C8H18 ) and Ethene

( C2H4 ) :

C10H22 (g)    →    C8H18 (g)    +    C2H4 (g)

Octane : Octane produced can be used to make Petrol

Ethene : Ethene can be used to make Poly (Ethene) - a type of plastic