reduction and oxidation and "negative sign"

[pizza1994]

1) 2F- --> F2 + 2e- E=-2.87 V
2) 2Cl- --> Cl2 + 2e- E= -1.36

whihc is the strongest reducing agent?
F- or Cl-

I would pick F- cause it has a value which is "more negative"......but the asnwer is Cl-......why

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[dnrs]

Remember that the more negative E is, the less favorable the forward reaction and the more favorable the reverse reaction is.

 

[pizza1994]

Remember that the more negative E is, the less favorable the forward reaction and the more favorable the reverse reaction is.

Isnt it that a strong reducing agent means a strong oxidation potential

In order to have a strong oxidation potential you prefer values that are the most negative and least positive......hence

the most negative value is for F- ......this seemed to work just fine in most cases.....

 

[dnrs]

No. The half reactions given show oxidation potentials, so the more positive is more favorable.

If the half reactions given showed reduction potentials (which is usually standard way of giving E values), then you would be correct because then, you would have to reverse the sign to get the E for the reverse reaction.

You have to know how to recognize reduction and oxidation potentials.

 

[Cawolf]

@pizza1994 you have the concept of oxidation/reduction correct, but what @dnrs posted is correct.

We are looking for the most favorable oxidation reaction, we are given oxidation reactions, so pick the most positive. The sign is only reversed if you are looking for the reverse reaction.

 

[pizza1994]

No. The half reactions given show oxidation potentials, so the more positive is more favorable.

If the half reactions given showed reduction potentials (which is usually standard way of giving E values), then you would be correct because then, you would have to reverse the sign to get the E for the reverse reaction.

You have to know how to recognize reduction and oxidation potentials.

so actually then it seems that its best to use your more logical approach where you have to keep in mind that high E means rxn is pushed in reverse direction. I tried this on a few questions and this seems to work fine too.

and yeah I also realized to be careful about whats given! thanks 🙂

 

[pizza1994]

@pizza1994 you have the concept of oxidation/reduction correct, but what @dnrs posted is correct.

We are looking for the most favorable oxidation reaction, we are given oxidation reactions, so pick the most positive. The sign is only reversed if you are looking for the reverse reaction.

so if you are given reduction and oxdiation potential in their standard format and you are asked for their respective strongest oxidzing and strongest reducing agents...then for both circumstances you always pick the "more positive" correct?

 

[dnrs]

@pizza1994 be careful though, negative not high E favors the reverse reaction.

 

[dnrs]

so if you are given reduction and oxdiation potential in their standard format and you are asked for their respective strongest oxidzing and strongest reducing agents...then for both circumstances you always pick the "more positive" correct?

Yes that is correct.

 

[pizza1994]

@pizza1994 be careful though, negative not high E favors the reverse reaction.

yes thanks 🙂