AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
The overall reaction in a hydrogen fuel cell involves the oxidation of…
Full specification wording
Fuel cells: The overall reaction in a hydrogen fuel cell involves the oxidation of hydrogen to produce water.
The overall chemical change in a hydrogen fuel cell is the oxidation of hydrogen to form water.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 3 of 5
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The overall chemical change in a hydrogen fuel cell is the oxidation of hydrogen to form water. Hydrogen is oxidised at one electrode and oxygen is reduced at the other, and the overall equation is 2H₂ + O₂ → 2H₂O. This means the only chemical product is water, which is why hydrogen fuel cells are described as producing no carbon dioxide at the point of use. The reaction releases energy electrochemically, producing a potential difference rather than heat alone. For example, in a hydrogen fuel cell vehicle, hydrogen from the tank and oxygen from the air combine to form water vapour, while electricity drives the motor. You should be able to state the overall reaction and identify hydrogen as the substance oxidised.
What earns the marks
- The overall reaction in a hydrogen fuel cell is hydrogen plus oxygen forming water.
- Hydrogen is oxidised in the overall reaction.
- The balanced overall equation is 2H₂ + O₂ → 2H₂O.
- Water is the only chemical product of the overall reaction.
- The reaction produces a potential difference as well as water.
Common mistakes and how to put them right
Writing the product as hydrogen peroxide instead of water.
Put it right by stating that the overall product is water, H₂O.
Forgetting to balance the equation.
Put it right by writing 2H₂ + O₂ → 2H₂O.
Saying that hydrogen is reduced.
Put it right by stating that hydrogen is oxidised and oxygen is reduced.
Exam tips
- Learn the balanced overall equation 2H₂ + O₂ → 2H₂O and use it when asked for the overall reaction.
- State clearly that hydrogen is oxidised and water is produced.
- If asked about environmental benefit, mention that the only product is water, avoiding claims beyond the specification.
Try the lesson
The start of the Fuel cells: The overall reaction in a hydrogen fuel cell involves the oxidation of hydrogen to produce water. lesson, made from checked teaching notes for this specification point.
Have a go first
What is the product of the overall reaction in a hydrogen fuel cell?
Listen
The overall chemical change in a hydrogen fuel cell is the oxidation of hydrogen to form water. Hydrogen is oxidised at one electrode and oxygen is reduced at the other, and the overall equation is 2H₂ + O₂ → 2H₂O. This means the only chemical product is water, which is why hydrogen fuel cells are described as producing no carbon dioxide at the point of use. The reaction releases energy electrochemically, producing a potential difference rather than heat alone. For example, in a hydrogen fuel cell vehicle, hydrogen from the tank and oxygen from the air combine to form water vapour, while electricity drives the motor. You should be able to state the overall reaction and identify hydrogen as the substance oxidised. A strong answer earns marks for these points. The overall reaction in a hydrogen fuel cell is hydrogen plus oxygen forming water. Hydrogen is oxidised in the overall reaction. The balanced overall equation is 2H₂ + O₂ → 2H₂O. Water is the only chemical product of the overall reaction. A common slip: Writing the product as hydrogen peroxide instead of water. Instead, stating that the overall product is water, H₂O. Exam tip: Learn the balanced overall equation 2H₂ + O₂ → 2H₂O and use it when asked for the overall reaction.
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Key words
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Hydrogen oxidation
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Water as a product
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Overall cell reaction
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See every definition
- Hydrogen oxidation
- In a hydrogen fuel cell, hydrogen is oxidised at one electrode while oxygen is reduced at the other.
- Water as a product
- The only chemical product of the overall reaction is water, which is why hydrogen fuel cells are described as producing no carbon dioxide at the point of use.
- Overall cell reaction
- The overall chemical change is hydrogen plus oxygen forming water, with the balanced equation 2H₂ + O₂ → 2H₂O.
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