Cracking

This lesson covers cracking of hydrocarbons as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand why cracking is carried out, the conditions for thermal and catalytic cracking, and the types of products formed.

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Why Is Cracking Needed?

Fractional distillation of crude oil produces fractions in fixed proportions. However, the demand for different fractions does not match the supply:

• There is high demand for short-chain hydrocarbons (petrol, gases) and alkenes (for making plastics).
• There is a surplus of long-chain hydrocarbons (heavy fuel oil, bitumen) that are less useful as fuels.

Cracking solves this problem by breaking long-chain hydrocarbons into shorter, more useful molecules.

What Cracking Produces

Cracking always produces:

• Shorter alkanes — used as fuels
• Alkenes — used to make polymers (plastics) and other chemicals

The general idea:

long-chain alkane → shorter alkane + alkene(s)

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Types of Cracking

There are two main types of cracking required by the specification:

1. Catalytic Cracking