# Determining the potential in a cell that is not at equilibrium concentrations.

1. Dec 2, 2011

### JustinLiang

1. The problem statement, all variables and given/known data
I attached a picture and I am confused by Part C.
The standard potential is given Eo=1.21

2. Relevant equations
Ecell=Eocell-RTlnQ/nF
R=8.3145
T=298.15
F=96485
Q=activity products/ activity reactants

3. The attempt at a solution
My problem with this question is finding Q.

Fe(s) -> Fe2+(aq) + 2e-
Fe3+(aq) + e- -> Fe2+(aq)

Balanced equation (is this right?):
2Fe3+(aq) + Fe(s) -> 3Fe2+(aq)

As suggested in the problem, the [Fe2+] of both half cells are different. Thus I do not know how to set up my Q, assuming that my balanced equation is correct.

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2. Dec 5, 2011

### Staff: Mentor

You can derive overall Nernst equation for the system starting with separate Nernst equations for each half cell. Just assume two separate potentials for each half cell initially, and combine them in the final equation - this will be the potential given as a standard one.