Explain why hydrogen-oxygen fuel cells are considered more advantageous than petrol engines for powering vehicles.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Engineers are designing a new fleet of buses for a city. They must choose between buses powered by petrol engines and buses powered by hydrogen-oxygen fuel cells.
Model answer (4 marks)
Fuel cells produce only water vapour as the exhaust, so they emit no harmful gases such as CO₂ or CO.
Petrol engines release CO₂, a greenhouse gas that contributes to global warming and climate change.
In a fuel cell the chemical energy of hydrogen is converted directly into electrical energy, giving a higher overall efficiency than the combustion process in petrol engines.
Hydrogen can be produced from renewable sources, and a fuel cell can run continuously as long as hydrogen and oxygen are supplied.
Petrol engines release CO₂, a greenhouse gas that contributes to global warming and climate change.
In a fuel cell the chemical energy of hydrogen is converted directly into electrical energy, giving a higher overall efficiency than the combustion process in petrol engines.
Hydrogen can be produced from renewable sources, and a fuel cell can run continuously as long as hydrogen and oxygen are supplied.
Examiner tips
- Use the exact phrases from the mark scheme – e.g. "water vapour", "no CO₂", "direct conversion", "renewable hydrogen".
- Show the comparison clearly: list the advantages in separate points to hit each mark.
Common mistakes
- Writing that fuel cells produce CO₂ or other pollutants.
- Failing to mention the renewable source of hydrogen or the continuous operation of the cell.
Mark scheme (4 marks)
- Fuel cells produce water (vapour) as the only product / no harmful exhaust emissions / no carbon dioxide or carbon monoxide produced
- Petrol engines release/produce carbon dioxide which contributes to global warming / climate change / greenhouse effect
- Fuel cells convert chemical energy directly into electrical energy / more efficient energy conversion than petrol engines
- Hydrogen can be produced from renewable sources / fuel cells operate continuously as long as hydrogen and oxygen are supplied
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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