A chemical cell is made from two different metal electrodes connected by an electrolyte. Explain why the voltage produced by a chemical cell eventually drops to zero, and explain why a hydrogen-oxygen fuel cell does not have this limitation.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
A chemical cell produces a voltage until one of the reactants (the metals or the electrolyte) is used up.
The reaction in a chemical cell is not continuous – it cannot be replenished, so the cell cannot be re‑charged or replaced.
A fuel cell is continuously supplied with hydrogen (fuel) and oxygen.
Therefore the hydrogen‑oxygen fuel cell continues to produce a voltage as long as hydrogen and oxygen are supplied and the reactants are not used up.
The reaction in a chemical cell is not continuous – it cannot be replenished, so the cell cannot be re‑charged or replaced.
A fuel cell is continuously supplied with hydrogen (fuel) and oxygen.
Therefore the hydrogen‑oxygen fuel cell continues to produce a voltage as long as hydrogen and oxygen are supplied and the reactants are not used up.
Examiner tips
- Use the word ‘until’ to link the drop in voltage to reactant depletion.
- Mention that the cell cannot be re‑charged – it is a one‑time reaction.
- State that a fuel cell is supplied continuously with fuel and oxidiser.
- Show the contrast: continuous supply vs. finite reactants.
Common mistakes
- Confusing the cell with a battery and implying it can be re‑charged.
- Failing to mention that the electrolyte is also consumed.
- Lacking the key point that a fuel cell is continuously fed with hydrogen and oxygen.
Mark scheme (4 marks)
- A chemical cell produces a voltage until one of the reactants (metals/electrolyte) is used up
- The reaction in a chemical cell is not continuous / cannot be replenished (cell is not recharged/replaced)
- A fuel cell is continuously supplied with hydrogen (fuel) and oxygen
- So the hydrogen-oxygen fuel cell continues to produce a voltage as long as hydrogen and oxygen are supplied / reactants are not used up
Key terms in this question
chemical cell · fuel cell · hydrogen-oxygen fuel cell · electrolyte · voltage
Related
- All Edexcel GCSE Chemistry (1CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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