requirement for a galvalnic cell (spoiler on AAMC11)

[kfsa1]

Hi guys,

I was wondering what the requirements for a galvanic cell was. My question came about due to a question on AAMC 11 where they give you a diagram of a cell with no indications of where the anode or the cathode was and the question asked: Will oxi-red occur spontaneously?

Now, I answered this question with a yes because as long as the two metals in question can produce a positive EMF, the cell will have negative G = spontaneous. This then got me to think what is the requirement (asides from the obvious set up with the salt bridge etc) for a galvanic cell? From the reduction potentials, I see that the only time -EMF will come about is when you have two of the same sign reduction potentials. I.E + + or - -.


Thank You!

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[indianjatt]

I believe electrolytic has to be non-spontaneous, + Delta G, - E Cell, and galvanic has to be spontaneous, - Delta G, + E Cell.

 

[movax]

I believe electrolytic has to be non-spontaneous, + Delta G, - E Cell, and galvanic has to be spontaneous, - Delta G, + E Cell.

This is correct. Think of your average AA battery; that reaction is spontaneous, as soon as you connect its terminals to a circuit, circuit begins to flow.

Electrolytic is the exact opposite, you could consider it recharging a battery.