Chemistry Cell Potential

[saltyload]

If I'm given 2 half reactions, both are shown being reduced and given their respective cell potentials, how do I tell which is being reduced/oxidized? Do I just reverse the reaction with the negative cell potential? Will there ever be a case where reduction and oxidation are assigned to 2 half reactions, yet one still has a negative cell potential?

Thanks.

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[loveoforganic]

More positive is more favorable. The more positive reduction potential will be the one reduced (in a galvanic cell). Neither of these reduction potentials is necessarily positive or negative alone.

I'm not sure what you mean exactly for your last question, but I think you're referring to an electrolytic cell.

 

[DougTPR]

If I'm given 2 half reactions, both are shown being reduced and given their respective cell potentials, how do I tell which is being reduced/oxidized? Do I just reverse the reaction with the negative cell potential? Will there ever be a case where reduction and oxidation are assigned to 2 half reactions, yet one still has a negative cell potential?

A technique I have used that requires virtually no thought is to figure out both combinations...

Ered1 - Ered2

Ered2 - Ered1

Whichever is positive is the cell potential for the spontaneous (Galvanic) cell and the reduction potential that is negative is the species that is oxidized.