Ethene (C₂H₄) can be produced by two different industrial methods: the cracking of ethane (from crude oil) and the dehydration of ethanol (from fermentation of glucose). Evaluate which method of producing ethene is more sustainable, giving reasons for your answer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Ethene is one of the most important industrial chemicals in the world, used to make poly(ethene) and many other products. Global demand for ethene continues to rise.
Model answer (5 marks)
1. Cracking of ethane uses crude oil, a non‑renewable, finite fossil‑fuel resource.
2. Fermentation of glucose (from plants) uses a renewable feedstock.
3. Cracking requires very high temperatures (≈800 °C) and therefore consumes large amounts of energy, making it energy‑intensive.
4. Dehydration of ethanol is essentially carbon‑neutral: the CO₂ released was originally absorbed by the plants during photosynthesis.
5. Therefore, the dehydration of ethanol is the more sustainable method because it uses a renewable raw material and is carbon‑neutral, whereas cracking relies on a finite resource and high energy input.
2. Fermentation of glucose (from plants) uses a renewable feedstock.
3. Cracking requires very high temperatures (≈800 °C) and therefore consumes large amounts of energy, making it energy‑intensive.
4. Dehydration of ethanol is essentially carbon‑neutral: the CO₂ released was originally absorbed by the plants during photosynthesis.
5. Therefore, the dehydration of ethanol is the more sustainable method because it uses a renewable raw material and is carbon‑neutral, whereas cracking relies on a finite resource and high energy input.
Examiner tips
- Use the exact terms from the mark scheme (non‑renewable, renewable, energy‑intensive, carbon‑neutral).
- Structure answer with numbered points matching the scheme.
- Give a clear conclusion that links the reasons to sustainability.
Common mistakes
- Confusing the energy source for the dehydration step; it is not a major energy consumer.
- Failing to mention the renewable nature of the glucose feedstock.
Mark scheme (5 marks)
- Cracking of ethane uses crude oil / a non-renewable / finite / fossil fuel resource
- Fermentation uses glucose from plants / a renewable feedstock (so dehydration of ethanol is more sustainable in terms of raw materials)
- Cracking requires high temperatures (and therefore uses large amounts of energy / is energy intensive), making it less sustainable
- Fermentation / dehydration of ethanol produces ethene that is effectively carbon neutral / does not add net CO₂ to the atmosphere because plants absorbed CO₂ when growing
- Reasoned conclusion stating that dehydration of ethanol / the plant-based route is more sustainable, with a linked reason (e.g. renewable feedstock / carbon neutral / long-term availability)
Key terms in this question
cracking · dehydration · fermentation
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Evaluate" question →
- Decode the mark scheme abbreviations →
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