AQA GCSE Chemistry

Revision Notes

1.1.4 Half Equations & Ionic Equations

Higher Tier Only

Half Equations & Ionic Equations

Half Equations

  • Half equations and ionic equations are specific types of equations for showing some of the fine details going on in chemical reactions
  • Half equations are used to show what happens to the electrons in reactions where atoms, molecules or ions are gaining or losing electrons
  • They are called half equations, because they represent only half of what is happening in a reaction involving electron transfer
    • One species gains electrons
    • Another species loses electrons
  • Examples of half equations are:

Pb2+ + 2e Pb

2Br  Br2 + 2e

Ionic Equations

  • Ionic equations are used to indicate what happens to ions during reactions
  • They help to simplify complicated processes where many substances are present, but only certain ions are actually reacting with each other
  • For example, we can use ionic equations to show what happens when an acid neutralizes and an alkali:

HCl + NaOH  → NaCl + H2O

  • Written out as an ionic equation would be

H+ + OH→ H2O

  • This is because sodium and chloride ions were present at the beginning and also at the end of the reaction, so they are unchanged
  • Ions which are present but do not take part in reactions are called spectator ions

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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