A city plans to replace its fleet of diesel buses with buses powered by hydrogen-oxygen fuel cells. Explain why this change would reduce the environmental impact of the city's public transport system.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Hydrogen‑oxygen fuel cells produce only water as a product, so the bus emits no harmful gases.
Diesel engines release CO₂, a greenhouse gas that drives climate change.
Diesel combustion also emits SO₂, NOx, particulates and CO, which deteriorate air quality and harm health.
Fuel cells are more efficient than diesel engines, wasting less fuel as heat, so less fuel is required for the same distance, further reducing emissions and resource use.
Diesel engines release CO₂, a greenhouse gas that drives climate change.
Diesel combustion also emits SO₂, NOx, particulates and CO, which deteriorate air quality and harm health.
Fuel cells are more efficient than diesel engines, wasting less fuel as heat, so less fuel is required for the same distance, further reducing emissions and resource use.
Examiner tips
- Use the exact phrases "produce only water" and "no harmful emissions" to hit the first point. Mention CO₂ and the pollutants SO₂, NOx, particulates and CO for the second and third points. Show the efficiency advantage to cover the fourth point. Keep each point short and to the point to fit the 4‑mark limit.
Common mistakes
- Writing that fuel cells emit CO₂ or other gases. Forgetting to mention the pollutants from diesel. Using vague terms like "cleaner" without specifying water or CO₂.
Mark scheme (4 marks)
- Hydrogen-oxygen fuel cells produce only water as a product / no harmful emissions from the fuel cell
- Diesel combustion produces carbon dioxide / CO2, which is a greenhouse gas contributing to climate change / global warming
- Diesel combustion produces pollutants such as sulfur dioxide / nitrogen oxides / particulates / soot / carbon monoxide, which harm air quality / health
- Fuel cells are more efficient than diesel engines / less fuel is wasted as heat, so less fuel is needed for the same journey, reducing overall resource use / emissions
Key terms in this question
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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