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# Electrode Potentials (EHell) (probably obvious) watch

1. Okay So!

In the Negative one we have:
V(2+)
V(3+)

In the positive:
VO(2+)
VO2(+) + H(+)

The data table :

V(3+) + e(-)---------------------------> V(2+)................. -.26V
VO(2+) +2H(+) +e(-) ------------------> V(3+) + H2O....... +.34V
O2 + 4H(+) + 4e(-) -------------------->2H2O ................ +0.68V
VO2(+) + 2H(+) + e(-)----------------->VO2(+) + H20........ +1.00V

Okay, so the markscheme says that the Ecell value is +1.26, Now while I know where this came from, my question is why?
Does the reaction to give the highest positive value always occur over other possible reactions.
Or are the other reactions actually infact not possible?
2. I'll even give rep! =D
3. What its not even being viewed...
Easy rep people come on!!
= /
4. (Original post by Fatal_Microbes)
What its not even being viewed...
Easy rep people come on!!
= /
who gives a flying **** about rep???

All you have to do is find two half reactinos (electrode potentials) that differ by the amount stated.

i.e. V(3+) + e(-)---------------------------> V(2+)................. -.26V
VO2(+) + 2H(+) + e(-)----------------->VO2(+) + H20........ +1.00V
5. (Original post by charco)
who gives a flying **** about rep???

All you have to do is find two half reactinos (electrode potentials) that differ by the amount stated.

i.e. V(3+) + e(-)---------------------------> V(2+)................. -.26V
VO2(+) + 2H(+) + e(-)----------------->VO2(+) + H20........ +1.00V

I was being sarcastic and trying to bump.

If you could tell me why the bottom reaction takes place?

I know that thats where the 1.26 comes from.
As thats 1.00-(-0.26)

My question is why does this
VO2(+) + 2H(+) + e(-)----------------->VO2(+) + H20........ +1.00V

Take place and not one of the other three that have a positive E-cell value.
Which is why I asked if it was because this one has the highest positive Ecell value, or if there is another reason which is being overlooked.
6. (Original post by Fatal_Microbes)
I was being sarcastic and trying to bump.

If you could tell me why the bottom reaction takes place?

I know that thats where the 1.26 comes from.
As thats 1.00-(-0.26)

My question is why does this
VO2(+) + 2H(+) + e(-)----------------->VO2(+) + H20........ +1.00V

Take place and not one of the other three that have a positive E-cell value.
Which is why I asked if it was because this one has the highest positive Ecell value, or if there is another reason which is being overlooked.
The reaction is driven by the fact that this has the highest cell potential (and can take place)

To look at driving forces you can consider the relationship between Gibbs free energy and electrode potentials.

ΔG = -nFEº

Hence the highest cell potental has the highest (negative) Gibbs free energy and is the most spontaneous reaction.
7. Brilliant,
Thank you very much!
8. Forgive me if i've misunderstood, but surely reaction 4 is the one that takes place just because you don't have the species for the other two? The V3+ ions aren't in contact with the VO(2+) ions anyway (assuming this is a normal electrochemical cell) and there is no acidified oxygen anywhere anyway. So then it's just normal redox **** blah blah blah

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