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# Feasibility of reaction in terms of E^o and Delta G ^o

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2. I think that reaction has caused the first eqn regarding Fe to be flipped/reversed.
Usually you would reverse the reaction with the more negative electrode potential.
So what you do (i think)
1) Rewrite the eqn regarding Fe, but reverse the reaction so you will get:
Fe<-> Fe(2+)+2e
2) Then cancel out your 2e on both eqns
By reversing the Fe eqn, you essentially flip the sign on the electrode potential, hence it becomes positive.
3. Hi Aclarke55

This question has nothing to do with delta G I think that page was referring to an earlier question! As for this question your two half equations give you a E value. The more negative the value the more likely it is going to be oxidised. For your example:

Fe2+ + 2e- --> Fe -0.44
Zn2+ + 2e- --> Zn -0.76

So the Zn will become Zn2+ (oxidised) because it is MORE negative than the first half equation. This means that when paired up the Fe2+ will gain two electrons and become Fe (reduced).

Now you can refer back to the original question which asks you if Fe + ZnSO4 would form Zn + FeSO4. You now know this is incorrect! The Zn would be oxidised and the Fe2+ would be reduced, OR you could say this reaction would happen instead: Zn+ FeSO4 --> ZnSO4 + FeSO4.

Another way of looking at feasibility is Ecell values. For the reaction suggested the Ecell value would be -0.3V. The negative sign tells you that this is not feasible. At this point I am unsure if you know Ecell values yet, so perhaps look them up afterwards?

Anyways I hope that helps.

Good luck

Alex
4. (Original post by ajsullivan)
Hi Aclarke55

This question has nothing to do with delta G I think that page was referring to an earlier question! As for this question your two half equations give you a E value. The more negative the value the more likely it is going to be oxidised. For your example:

Fe2+ + 2e- --> Fe -0.44
Zn2+ + 2e- --> Zn -0.76

So the Zn will become Zn2+ (oxidised) because it is MORE negative than the first half equation. This means that when paired up the Fe2+ will gain two electrons and become Fe (reduced).

Now you can refer back to the original question which asks you if Fe + ZnSO4 would form Zn + FeSO4. You now know this is incorrect! The Zn would be oxidised and the Fe2+ would be reduced, OR you could say this reaction would happen instead: Zn+ FeSO4 --> ZnSO4 + FeSO4.

Another way of looking at feasibility is Ecell values. For the reaction suggested the Ecell value would be -0.3V. The negative sign tells you that this is not feasible. At this point I am unsure if you know Ecell values yet, so perhaps look them up afterwards?

Anyways I hope that helps.

Good luck

Alex
The students are expected to know that ΔG = -nFEº

They can then use the electrode potentials to also calculate ΔG values.
5. Sorry I missed this - not in my own specification (or most of the ones I deal with actually), and reading it sideways didn't help! Either way the answer is correct but not in terms of deltaG! Good spot though, thank you.

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