[wytw]

Hello everyone,

For the oxygen reduction in aqueous solution :
O₂(aq) + 2H⁺(aq) +2e  H₂O₂(aq)
(the correct state for H₂O₂ is liquid or aqueous ?)

My question is how to write the nernst equation ? Because in my case it is relevant to use the concentration of oxygen and not the partial pressure as in standard conditions, so how can I express the formal potential ? I didn't find any values for it...

Thanks for your help ! 

[Borek]

(the correct state for H₂O₂ is liquid or aqueous ?)

Why the doubt?

My question is how to write the nernst equation ? Because in my case it is relevant to use the concentration of oxygen and not the partial pressure as in standard conditions, so how can I express the formal potential ?

No idea what you are doing that excludes use of the partial pressure, but do you know Henry's law?

[wytw]

Thanks for replying !

Its about electrochemical experiments so the oxygen is dissolved in water and not considered as gaseous.

And yes I know Henry's law, so I know the concentrations, my question was more about writing the "correct" form of the Nernst equation in this case, owning this.

[Borek]

Gaseous oxygen is always in equilibrium with the dissolved one, so both versions - using concentration and the partial pressure - are correct and equivalent.

[wytw]

In resume ?
E=E⁰ - RT/2F ln([H₂O₂]/(c_O2/H_O2*[H⁺]²)
Where H is the Henry constant of oxygen expressed in term of molarity.

Thanks !