A shipping company is considering switching its large cargo vessels from using heavy fuel oil to using hydrogen gas as a fuel. Evaluate the use of hydrogen as a fuel for the cargo vessels compared to heavy fuel oil.

OCR A-Level Chemistry B: Salters (H433) — DF Developing fuels · Evaluate · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Heavy fuel oil is a hydrocarbon fuel obtained from crude oil. It releases large amounts of energy when burned but produces several products of combustion. Hydrogen can be produced by electrolysis of water and burns to produce only one product.

Model answer (5 marks)

1. Hydrogen combustion gives only H₂O, so no CO₂ is released, avoiding greenhouse‑gas emissions.
2. Burning heavy fuel oil emits CO₂, SO₂, CO and particulates, contributing to pollution and climate change.
3. Hydrogen can be produced by electrolysis of water, making it a renewable fuel that does not deplete fossil‑fuel reserves.
4. Electrolysis requires large amounts of electricity; if this electricity comes from fossil fuels, the overall carbon footprint may still be high.
5. Hydrogen is a gas, highly flammable and difficult to store and transport safely, making it a practical disadvantage for large cargo vessels.

Examiner tips

  • Use the exact terminology (e.g. CO₂, SO₂, electrolysis).
  • Show a clear comparison: advantages first, then disadvantages.
  • Keep each point brief but complete – 1 mark each.

Common mistakes

  • Confusing hydrogen combustion with heavy fuel oil combustion.
  • Ignoring the energy source for electrolysis.

Mark scheme (5 marks)

  1. Hydrogen combustion produces only water (and no carbon dioxide), so it does not contribute to the greenhouse effect / global warming
  2. Heavy fuel oil produces carbon dioxide (and other pollutants such as carbon monoxide / sulfur dioxide / particulates) when burned, which contributes to pollution / climate change
  3. Hydrogen can be produced from water by electrolysis, so it can be renewable / does not deplete crude oil reserves, unlike heavy fuel oil which is a non-renewable fossil fuel
  4. Electrolysis requires a large amount of electrical energy, so hydrogen production may still cause pollution / carbon emissions if the electricity comes from fossil fuels
  5. Hydrogen is difficult / expensive to store and transport safely because it is a gas and highly flammable, which is a practical disadvantage for use in cargo vessels

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