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Topic: Nernst equation  (Read 1693 times)

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Offline wytw

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Nernst equation
« on: October 23, 2016, 04:59:07 AM »
Hello everyone,

For the oxygen reduction in aqueous solution :
O2(aq) + 2H+(aq) +2e  ::equil:: 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 !  :)

Offline Borek

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Re: Nernst equation
« Reply #1 on: October 23, 2016, 01:55:06 PM »
(the correct state for H2O2 is liquid or aqueous ?)

Why the doubt?

Quote
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?
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Offline wytw

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Re: Nernst equation
« Reply #2 on: October 23, 2016, 04:45:14 PM »
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.


Offline Borek

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Re: Nernst equation
« Reply #3 on: October 23, 2016, 05:54:19 PM »
Gaseous oxygen is always in equilibrium with the dissolved one, so both versions - using concentration and the partial pressure - are correct and equivalent.
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Offline wytw

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Re: Nernst equation
« Reply #4 on: October 24, 2016, 10:10:18 AM »
In resume ?
E=E0 - RT/2F ln([H2O2]/(cO2/HO2*[H+]2)
Where H is the Henry constant of oxygen expressed in term of molarity.

Thanks !

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