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 · View as Markdown

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

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.

Model answer (4 marks)

Hydrogen combustion gives only H₂O, so no CO₂ or other carbon‑based greenhouse gases are released, unlike petrol combustion which emits CO₂, CO, unburnt hydrocarbons and particulates that worsen climate change and air quality.
A major obstacle is the storage and distribution of hydrogen: it has a very low density, requiring high‑pressure tanks or cryogenic liquid storage and specialised, costly infrastructure, which limits its widespread use as a transport fuel.

Examiner tips

  • Use the word ‘only’ to highlight the absence of CO₂ in hydrogen combustion; mention CO₂, CO, unburnt hydrocarbons for petrol. State the storage problem clearly – low density, high pressure or cryogenic. Keep answer within 4 marks, use concise sentences.

Common mistakes

  • Confusing hydrogen combustion with fuel cells – both produce water, but fuel cells are more efficient. Forgetting to mention the high pressure/cryogenic requirement. Failing to note that most hydrogen is currently fossil‑fuel derived, which reduces its environmental benefit.

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.

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