Disproportionation & Electrode Potential (Edexcel A Level Chemistry)

• A disproportionation reaction is where one element in a chemical is simultaneously reduced and oxidised, e.g.

2Cu⁺ (aq) → Cu²⁺ (aq) + Cu (s)

• Standard electrode potentials can be used to explain disproportionation reactions

1. • 1. Cu²⁺ (aq) + e^– ⇌ Cu⁺ (aq)   E^θ = +0.15 V
     2. Cu⁺ (aq) + e^– ⇌ Cu (s)  E^θ = +0.52 V
   • The electrode potential value for equation 1 is more negative, therefore, this reaction will be the oxidation reaction and proceed to the left
   • The electrode potential value for equation 2 is more positive, therefore, this reaction will be the reduction reaction and proceed to the right
     • You now have:

Cu⁺ (aq) ⇌ Cu²⁺ (aq) + e^– 

    Cu⁺ (aq) + e^– ⇌ Cu (s)  

• • • Combining these two equations agrees that the overall equation is possible 

2Cu⁺ (aq) → Cu²⁺ (aq) + Cu (s)