# Explain why the use of hydrogen as a fuel is considered environmentally advantageous compared to the use of petrol (gasoline), and outline one significant challenge that currently limits the widespread adoption of hydrogen as a transport fuel.

> IB DP Chemistry Higher Level (2023 syllabus) — R1.3 Energy from fuels · Explain · 4 marks

> Hydrogen can be combusted in engines or used in fuel cells to power vehicles. It has been proposed as a clean alternative to petrol (gasoline), which is a complex mixture of hydrocarbons.

## Mark scheme (4 marks)

1. Combustion of hydrogen produces only water as a product, so no carbon dioxide (or other carbon-containing greenhouse gases) is released directly.
2. Petrol combustion releases carbon dioxide (a greenhouse gas) as well as other pollutants such as carbon monoxide, unburnt hydrocarbons, or particulates, contributing to climate change and air pollution.
3. A significant challenge is the storage and distribution of hydrogen: it has a very low density as a gas and must be stored under very high pressure or as a cryogenic liquid, requiring specialised, expensive infrastructure.
4. Most hydrogen is currently produced from fossil fuels (e.g., steam reforming of methane), which still releases CO₂, undermining the environmental benefit unless renewable energy sources are used to produce 'green' hydrogen.

## Related

- [Revision notes for IB DP Chemistry Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-use-of-hydrogen-8ac2061f) · Published by Druglandscape Ltd.