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Author Topic: Confusion about Galvanic Cell Question  (Read 607 times)

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astuart

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Confusion about Galvanic Cell Question
« on: November 25, 2012, 10:05:18 PM »

Could someone please clarify what is meant by the following statement? 
"Write the balanced equation for the reaction occurring in the cell as 2 mol of electrons flow from left to right in the external circuit".

This is basically just in regards to voltaic cells, and the majority of the questions I've dealt with have either had no mention of the moles of electrons that flow through the circuit, or they've only mentioned one.  What am I supposed to do in this case?
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Borek

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Re: Confusion about Galvanic Cell Question
« Reply #1 on: November 25, 2012, 10:25:20 PM »

Ignore the moles of electrons for now. What is the reaction?

(Could be it is just a lousy wording, but knowing the context first won't hurt).
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astuart

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Re: Confusion about Galvanic Cell Question
« Reply #2 on: November 25, 2012, 10:37:12 PM »

Ignore the moles of electrons for now. What is the reaction?

(Could be it is just a lousy wording, but knowing the context first won't hurt).

The cell is as follows...
Cd | Cd(2+)(aq) || Ni(2+)(aq) | Ni
The question itself asks me to calculate the redox reaction, the standard cell potential, DeltaG, the Equilibrium Constant, and also the cell potential if the Cadmium cell is 0.010M and the Nickel cell is 1 M.

So...
Ox = Cd -> Cd(2+) + 2e
Red = Ni(2+) + 2e -> Ni
The reduction potential for cadmium and nickel -0.40V and -0.25V respectively.
So, Ecell = -0.25 + 0.4 = 0.15

DeltaG = -2(96485)(0.15)
= -28945J / -28.9 kJ

K = e^{2(96485)(0.15) / 8.314(298)}
= 118,540 (or 1.2 x 10^5)

Using Nernst Equation...
0.15 - [8.314(298) / 2(96485)] ln [1/0.01]
= 0.15 - (0.012839156)(4.605170186)
= 0.15 - 0.0591265
= 0.0908V

I'm not sure if I'm calculating all of this right - the equilibrium constant seems quite high for my liking, but not too sure...
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Borek

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Re: Confusion about Galvanic Cell Question
« Reply #3 on: November 26, 2012, 04:07:47 AM »

Lousy wording probably. Balanced reaction contains 2 electrons (moles of electrons) so I would assume it is already what they ask for.

105 is not much for the equilibrium constant.

I just skimmed over your calculations - nothing cries out loud "I AM WRONG", but I could miss something.
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