# 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

> 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.

## 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

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](https://www.gradenine.co.uk/learn)
- [How to answer "Evaluate" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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