GCSE Chemistry (AQA)

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Cracking

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Organic chemistry Carbon compounds as fuels and feedstock

Cracking

8:57 Hydrocarbons
Spec 4.7.1.4
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  • Hydrocarbons can be broken down into smaller, more useful molecules through a process called cracking.
  • Cracking can produce smaller molecules from larger hydrocarbons, such as breaking an eight-carbon atom hydrocarbon into molecules with six and two carbon atoms.
  • The molecules produced by cracking are generally more useful than the larger alkanes.
  • Cracking can be done by various methods, including catalytic cracking and steam cracking.
  • Catalytic cracking involves heating alkanes to a vapor and passing them over a hot catalyst, typically at around 550 degrees Celsius.
  • Steam cracking involves heating alkanes to a very high temperature without a catalyst, reaching about 800 degrees Celsius, and mixing with steam.
  • The products of cracking include alkanes and alkenes, with alkenes containing a double bond between two carbon atoms.
  • Alkenes are more reactive than alkanes and react with bromine water, which turns from brown to colorless in their presence.
  • The number of carbon and hydrogen atoms in the products of cracking will be the same as in the original alkane.
  • An example of a cracking equation: C6H14 can be cracked into C4H10 and C2H4.
  • Cracking is useful because there is a high demand for fuels with small molecules, which have lower boiling points, are less viscous, and are more flammable.
  • Alkenes produced from cracking are used to produce polymers and as starting materials for other chemicals.
  • Polymers, like polyethene, can be made by joining alkenes through polymerization.

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