Concentration of anodes and cathodes in Q/K

[Tanya Nguyen 1B]

For the equations, E=E°-(RT/nF)lnQ or E°=(RT/nF)lnK, Q and K is [products]/[reactants] and given the concentration of the anode and cathode, why is it [anode]/[cathode] and not the other way around?

[Jeffrey Doeve 2I]

Hi Tanya, it is anode/cathode because of the logic of half reactions. If we had a concentration cell with Ag->Ag+ + e- and Ag+ + e- -> Ag, the Ag would cancel out. Notice how we cannot cancel the Ag+ because they are at different concentrations and how the one where oxidation is occurring(anode) has Ag+ on the product side. In a way, you could say a more representative form of Q/K(products/reactants) would be (Ag+ of anode/Ag+ of cathode).