IB Chemistry SL

Revision Notes

9.1.5 Half Equations

Half Equations

  • Oxidation numbers can be used to balance chemical equations
  • Go through these steps to balance a redox equation:
    1. Write the unbalanced equation and identify the atoms which change in ox. no.
    2. Deduce the ox.no. changes
    3. Balance the ox.no. changes
    4. Balance the charges
    5. Balance the atoms

Worked Example

Manganate(VII) ions (MnO4) react with Fe2+ ions in the presence of acid (H+) to form Mn2+ ions, Fe3+ ions and water

Write the overall redox equation for the reaction

Answer:

Step 1: Write the unbalanced equation and identify the atoms which change in ox. no.

Electrochemistry Step 1 Writing overall redox reactions, downloadable AS & A Level Chemistry revision notes

Step 2: Deduce the ox.no. changes

Electrochemistry Step 2 Writing overall redox reactions, downloadable AS & A Level Chemistry revision notes

Step 3: Balance the ox.no. changes

Electrochemistry Step 3 Writing overall redox reactions, downloadable AS & A Level Chemistry revision notes

Step 4: Balance the charges

Electrochemistry Step 4 Writing overall redox reactions, downloadable AS & A Level Chemistry revision notes

Step 5: Balance the atoms

Electrochemistry Step 5 Writing overall redox reactions, downloadable AS & A Level Chemistry revision notes

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