Redox Reaction in Terms of Change of Oxidation Number

Oxidation and Reduction in Term of Changes of Oxidation State

Oxidation involves an increase in oxidation state
Reduction involves a decrease in oxidation state
  1. Another way to determine oxidation and reduction is to see the change of the oxidation state after a reaction.
  2. An atom is said to be oxidised when its oxidation state increases.
  3. An atom is said to be reduced when its oxidation state decreases.


  1. The magnesium’s oxidation state has increased by 2, from 0 to +2. Therefore, it has been oxidised.
  2. The hydrogen’s oxidation state has decreased by 1, from +1 to 0. Therefore it has been reduced.
  3. The chlorine is in the same oxidation state on both sides of the equation – it hasn’t been oxidised nor reduced.


There is no change of oxidation state for all elements. This isn’t a redox reaction.


  1. In this example, we can see that the oxidation state of chlorine has increased and also decreased.
  2. Chlorine is oxidised and reduced, at the same time.
  3. This is a good example of a disproportionation reaction. A disproportionation reaction is one in which a single substance is both oxidised and reduced.

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