Why Does Chlorine Gas Form at the Anode in the Chlor-Alkali Process?

[shikobe]

Redox reaction...with a twist!

In the chlor-alkali process OH–(aq) and Cl2(g) are produced by the electrolysis of a saturated solution of sodium chloride. Explain why chlorine gas rather than oxygen gas forms at the anode.


The solution to the question has the word "Overpotential" and I tried googling the meaning and ended up confusing myself:S Could someone please explain to me how this thing works...?

Much Appreciated.

 

[Borek]

Oxygen electrode reactions are slow (no idea about explanation, that's just the way they are). To speed them up you can apply higher potential (overpotential). However, when you apply higher potential, it may happen other things start to react.

 

[shikobe]

Thx for your explanation, I think I understood that but could anybody explain why it happens that Oxygen has a much higher overpotential and could somebody clarify what overpotential means in the context of this question?

 

[Borek]

Overpotential means for the reaction to proceed you need to apply much higher potential than the one given by the Nernst equation. This difference (real minus Nernstian) is called overpotential.