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Physical Chemistry

Cool goIITian

 Joined: 3 Sep 2008 Post: 71
5 Dec 2008 18:26:21 IST
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emf
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Eo (Fe3+|fe) = -x

Eo (Fe2+|fe) = -y

Then Eo (Fe3+|fe2+) =     z

We here use

-Fz =  -3F(-x)  - 2F(y)

Z= -3x + 2y

Why not this way

Z=-x + y   as we do in  finding value of Eo   cell

New kid on the Block

Joined: 4 Dec 2008
Posts: 26
5 Dec 2008 19:57:37 IST
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This is beacuse we cannot just add the emf values directly . We have to add the Gibbs Free Energy and then calculate standard potentials indirectly. This is beacuse the Gibbs Free Energy of the resulting rxn is equal to the sum of the Gibbs Free Energy  of the first two reactions. (By basic definition of enthalpy).

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Cool goIITian

Joined: 3 Sep 2008
Posts: 71
6 Dec 2008 11:29:19 IST
1 people liked this

then why we add in finding emf 0f cell as

emf=oxd. pot of oxidation half reaction + red. pot of reduction half reaction

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