Ethene is an important organic compound produced during the cracking of crude oil fractions. Describe what is meant by cracking and explain why ethene is a more useful product than the large hydrocarbon molecules from which it is made.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Cracking is the process of breaking down large hydrocarbon molecules into smaller ones.
Cracking requires high temperature (and often a catalyst or steam).
Ethene is an alkene, containing a carbon–carbon double bond.
Because of this double bond, ethene is more reactive and can undergo addition reactions.
Ethene is used to make polymers and plastics (addition polymerisation) and is also used as a fuel, making it more useful than the large hydrocarbon fractions from which it is produced.
Cracking requires high temperature (and often a catalyst or steam).
Ethene is an alkene, containing a carbon–carbon double bond.
Because of this double bond, ethene is more reactive and can undergo addition reactions.
Ethene is used to make polymers and plastics (addition polymerisation) and is also used as a fuel, making it more useful than the large hydrocarbon fractions from which it is produced.
Examiner tips
- Use the term "cracking" and mention high temperature or catalyst. State that ethene is an alkene with a C=C bond. Explain its reactivity and addition polymerisation. Mention its industrial uses (plastics, fuel).
Common mistakes
- Confusing cracking with distillation. Forgetting to mention the double bond. Saying ethene is useful only because it is a gas, not its reactivity.
Mark scheme (5 marks)
- Cracking involves breaking down large hydrocarbon molecules into smaller ones
- Cracking requires high temperature (and a catalyst or steam)
- Ethene is an alkene / contains a carbon-carbon double bond
- Ethene is more reactive / can undergo addition reactions (due to the double bond)
- Ethene is used to make polymers / plastics (addition polymerisation) OR used as a fuel / in greater demand than large fractions
Key terms in this question
Related
- All WJEC A-Level Chemistry (Wales) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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