Cracking
Contents
Key Stage 4
Meaning
Cracking is a Thermal Decomposition process in which large hydrocarbon molecules are broken into smaller hydrocarbon molecules.
About Cracking
- Cracking is often done because Crude Oil contains more large hydrocarbon molecules than can be used and not enough short hydrocarbon molecules than are needed.
- When Crude Oil fractions are cracked the long alkanes are broken down into smaller alkanes and alkenes.
- Cracking is done at very high temperatures (500°C) and uses either a catalyst to aid the reaction or steam.
- When an alkane is cracked into smaller pieces there are not enough Hydrogen [[atom]s to produce two saturated hydrocarbons. One of the hydrocarbons must be unsaturated and therefor will have a double bond.
Examples
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| If butane were cracked. | An alkane and an alkene are produced. | |||
Cracking a hydrocarbon can produce many possible products:
Hexadecane → Decane + Hexene
- <chem>C16H34 -> C10H22 + C6H12</chem>
Hexadecane → Decane + Butene + Ethene
- <chem>C16H34 -> C10H22 + C4H8 + C2H4</chem>
Decane → Pentane + Pentene
- <chem>C10H34 -> C5H12 + C5H10</chem>
Decane → Hexane + Butene
- <chem>C10H34 -> C6H14 + C4H8</chem>
References
AQA
- Cracking (of hydrocarbons), page 149, GCSE Combined Science; The Revision Guide, CGP, AQA
- Cracking (of hydrocarbons), page 226, 227, GCSE Chemistry, CGP, AQA
- Cracking (of hydrocarbons), page 77, GCSE Chemistry; The Revision Guide, CGP, AQA
- Cracking (of hydrocarbons), pages 194, 195, GCSE Combined Science Trilogy; Chemistry, CGP, AQA
- Cracking, pages 147-8, GCSE Combined Science Trilogy 2, Hodder, AQA
- Cracking, pages 154-55, GCSE Chemistry; Third Edition, Oxford University Press, AQA
- Cracking, pages 176-7, GCSE Chemistry, Hodder, AQA
- Cracking, steam, page 236, GCSE Chemistry; Student Book, Collins, AQA
- Cracking; catalytic, page 236-7, GCSE Chemistry; Student Book, Collins, AQA
Edexcel
- Cracking, page 140, GCSE Combined Science; The Revision Guide, CGP, Edexcel
- Cracking, page 274, GCSE Combined Science, Pearson Edexcel
- Cracking, page 90, GCSE Chemistry; The Revision Guide, CGP, Edexcel
- Cracking, pages 160, 190, GCSE Chemistry, Pearson, Edexcel
- Cracking, pages 262, 263, GCSE Chemistry, CGP, Edexcel