# Redox Reactions and standard emf calculations

What is the equation I should be using for the following question:

At 298K a cell reaction has a standard emf of +0.17V. The equilibrium constant for the cell reaction is 5.5 X 10^5. What is the value of n for the cell reaction.

Grateful for anyone's help!

Borek
Mentor
What equations have you learned while studying redox potentials?

E°cell = E°cathode - E°anode
E°cell = (RT/nF)(lnk)
E = E° - (0.0592/n)(logk)

Borek
Mentor
Why don't you just select the equation containing all known values and n? This is almost a simple plug and chug.

The equation that should be most likely used is E = E°-(0.0592/n)(logk).
I have the value for the standard emf = E°, and value of k.

Do I assume E to be zero then? If I do so, then the solution should look like the following:
0= E° - (0.0592/n)(logk)
0= 0.17 - (0.0592/n)(log(5.5*10^5))
0.17 = (0.0592/n)(log(5.5*10^5))
n= (0.0592)(log(5.5*10^5)) / 0.17
n= 1.9989

Borek
Mentor
Yes.

When Q=K cell potential is zero.

Thank you for the help!