Nernst Equation in Concentration Cells

[justadream]

E = E_Standard - (.059 / n) logQ

Q should be products over reactants.

In concentration cells, how do you know what are the "products" and what are the "reactants"?

I see in a TBR question (TBR GC Book II page 298 #79) that they use [Anode] / [Cathode]

which is equal to

[lesser concentration] / [higher concentration]

for concentration cells. Can someone explain more intuitively why this is?

---

Members don't see this ad.

 

[Chrisz]

for concentration cells the standard voltage between the two containers is simply zero, because the metals and ions are exactly the same in the two containers. The voltage between the two containers are set up by the difference in the concentration of ions. E=-0.059/n(logQ). If Q is not equal to 1, the concentration of the ions in the two containers are not equal, they will not be equilibrium, so they will simply adjust to make a 1:1 ratio where logQ=log1=0 and E=0. So a concentration cell's cathode and anode is determined by which side has more cation and which side has less cations. the side with more cations will be considered cathode and the side with less will be considered anode.