Cell voltage

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chiddler

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I understand this question now. I typed it up already so....

maybe it'll help somebody.

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"In a galvanic cell, the Ereduction + Eoxidation must be greater than 0 volts. If Eoxidation is greater than 0 volts, the overall voltage is positive so choices B and D are galvanic cells an are eliminated. The only way that Ecell can be less than 0 when Ereduction is positive is when Eoxidation is a negative value with a magnitude greater absolute value than Ereduction. The best answer choice is C."
 
E must be positive for the reaction to be spontaneous:

dG = -nFE<-must be +

So B and D would be spontaneous on the first virtue. Now A and C.

I'm stuck here, will get back to it later unless someone wants to chime in?
 
E must be positive for the reaction to be spontaneous:

dG = -nFE<-must be +

So B and D would be spontaneous on the first virtue. Now A and C.

I'm stuck here, will get back to it later unless someone wants to chime in?

The explanation is pretty clear. Ecell = Ered + Eox. The only way Ecell is negative when Ered is positive is when abs(Eox) > abs (Ered).
 
yes. i tend to skip details in the question. the moment i noticed the "greater than 0" part, I understood it. it just took me a long time to figure this out.
 
yes. i tend to skip details in the question. the moment i noticed the "greater than 0" part, I understood it. it just took me a long time to figure this out.

These types of problems and answer choices are why I think TBR is so far ahead of the other prep companies. It's not a difficult question, but the answers are presented in such a weird way with multiple parts to each answer that it can be very time consuming if you aren't used to it.
 
Don't get it but will look at tomorrow.

Just flip everything in your mind. For you to have a positive E and thus negative deltaG, you need the reduced species to have a positive value that's higher in absolute value than the oxidized species- otherwise the large negative value of the Eox would make Ecell negative. When you turn a reduction potential into an oxidation potential, you flip it. So for a negative deltaG, you need a negative Ecell and for this you need your oxidized species to have a negative value and for the absolute value to be greater than the reduced species, otherwise it's positive Ered will make Ecell positive.
 
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