Posted by **bekah** on Friday, May 2, 2014 at 4:46pm.

Construct a galvanic (voltaic) cell from the half reactions shown below.

Au3+ + 3 e- → Au (s) ξo= 1.420 V

Br2 (l) + 2 e-→ 2 Br- (aq) ξo= 1.087 V

Calculate the equilibrium constant (K) for this cell. Assume that the temperature is 298K.

First, consider what happens to the Nernst equation when the system reaches equilibrium:

ξ = ξo - (RT/nF) ln Q

What is ξ when the system has reached equilibrium? Is there any driving force left?

Remember that ∆G = -nFξ.

At equilibrium, ∆G = 0, so ξ = 0, too.

At equilibrium, Q = K, since all reactants and products are present at their equilibrium concentrations.

This simplifies the Nernst equation to:

ξocell = [(RT)/nF] ln K

Now calculate a value for K.

You may need to use scientific notation to record your answer. If so, enter it as: 4E43 which is equivalent to 4x1043

- chemistry -
**Anonymous**, Tuesday, March 24, 2015 at 10:31pm
Use second equation

1.420- (-1.087)= .333

Use that as cell potential.

R=8.314

T=298

n= 6 mols electrons because you have to multiply the two reactions to get 6 electrons so you can cancel the electrons out

F=96,500

.333= 0.004279lnQ

divide both sides by .00427 to cancel it from the right side

.333/.00427=77.82

77.82=lnQ

enter in calculator 2nd and ln to get e^ (77.82) because you want to get ride of ln from the right side so its pushed to the left side as its inverse of e^ (77.82) and ln cancels out so youre left with Q.

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