Half Equation
Contents
Key Stage 4
Meaning
A half equation is a type of symbol equation which shows how individual ions gain or lose electrons at an electrode during electrolysis.
About Half Equations
- In half equations only one ion is considered at a time, or the changes at one electrode.
- Half equations use the letter 'e' to represent electrons.
- Half equations can be taken from balanced symbol equations.
- The total charge on each side of a half equation must add to zero.
- The number of each element must be the same on both sides of a half equation.
Examples
Balanced Symbol Equation | 2Li_{2}O(l) → 4Li(l) + O_{2}(g) | CuCl_{2}(aq) → Cu(s) + Cl_{2}(g) | 2H_{2}O(l) → 2H_{2}(g) + O_{2}(g) |
Half Equation at cathode | Li^{+} + e^{-} → Li | Cu^{+2}(aq) + 2e^{-} → Cu(s) | 2H^{+}(aq) + 2e^{-} → H_{2}(g) |
Half Equation at anode | 2O^{-2} → O_{2} + 4e^{-} | 2Cl^{-}(aq) → Cl_{2}(g) + 2e^{-} | 4OH^{-} → 2H_{2}O(l) + O_{2}(g) + 4e^{-} |
References
AQA
- Half equations, pages 104, 289-91, GCSE Chemistry, Hodder, AQA
- Half equations, pages 142-144, GCSE Combined Science Trilogy; Chemistry, CGP, AQA
- Half equations, pages 167-169, GCSE Chemistry, CGP, AQA
- Half equations, pages 206, 255-7, GCSE Combined Science Trilogy 1, Hodder, AQA
- Half equations, pages 59, 65, GCSE Chemistry; The Revision Guide, CGP, AQA
- Half-equations, pages 87, 104-105, 107, 108, 123, GCSE Chemistry; Third Edition, Oxford University Press, AQA
Edexcel
- Half equations, pages 110-112, GCSE Combined Science; The Revision Guide, CGP, Edexcel
- Half equations, pages 134, 135, GCSE Chemistry, CGP, Edexcel
- Half equations, pages 210, 225, 231, GCSE Combined Science, Pearson Edexcel
- Half equations, pages 48-50, GCSE Chemistry; The Revision Guide, CGP, Edexcel
- Half equations, pages 66, 81, 87, GCSE Chemistry, Pearson, Edexcel