Chemical Reactions
Most textbooks present the following model for the chemical reactions of a lemon battery. When the cell is providing an electrical current through an external circuit, the metallic zinc at the surface of the zinc electrode is dissolving into the solution. Zinc atoms dissolve into the liquid electrolyte as electrically charged ions (Zn2+), leaving 2 negatively charged electrons (e-) behind in the metal:
- Zn → Zn2+ + 2e- .
This reaction is called oxidation. While zinc is entering the electrolyte, two positively charged hydrogen ions (H+) from the electrolyte combine with two electrons at the copper electrode's surface and form an uncharged hydrogen molecule (H2):
- 2H++ 2e- → H2 .
This reaction is called reduction. The electrons used from the copper to form the molecules of hydrogen are made up by an external wire or circuit that connects it to the zinc. The hydrogen molecules formed on the surface of the copper by the reduction reaction ultimately bubble away as hydrogen gas.
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