A simple chemical cell (electrochemical cell) generates a voltage when two different metals are connected in an electrolyte solution.
- The two metals act as electrodes.
- The electrolyte (e.g. dilute acid or salt solution) allows ions to move between the electrodes.
- The more reactive metal loses electrons more readily — it acts as the negative electrode (anode in a cell).
- Electrons flow through the external circuit from the more reactive metal to the less reactive metal.
Key rule: The greater the difference in reactivity between the two metals, the larger the voltage produced.
Examples
| Pair of metals | Relative reactivity difference | Relative voltage |
|---|---|---|
| Zinc / Copper | Large | Higher |
| Iron / Copper | Medium | Medium |
| Tin / Copper | Small | Lower |
| Copper / Copper | None (same metal) | Zero |
Quick Check: A cell uses magnesium and zinc electrodes. A second cell uses iron and copper electrodes. Which cell produces a larger voltage, and why?
The magnesium/zinc cell. Magnesium is much more reactive than zinc, giving a larger reactivity difference — and therefore a larger voltage — than the iron/copper pair.
This deep dive covers Simple Chemical Cells within Fuel Cells for GCSE Chemistry. Revise Fuel Cells in Energy Changes for GCSE Chemistry with 5 exam-style questions and 6 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 3 of 13 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Fuel Cells
A simple electrochemical cell is made by placing two different metal electrodes into an electrolyte. Which statement correctly describes what affects the voltage produced?
Compare a non-rechargeable alkaline battery with a rechargeable lithium-ion battery. Give one advantage and one disadvantage of the rechargeable battery.