[Ai]

I had a question for calculating the emf of galvanic cell for equal concentration at both anode and cathode, and when they are at unequal concentration.

When you have equal concentrations then you simple use the half reactions of both ends to calculate the emf. But when you have unequal concentrations you calculate the emf with the half reactions at both ends in addition to using the Nernst equation, where Q in the equation is [Anode]/[Cathode]?

[LQ43]

When you have equal concentrations then you simple use the half reactions of both ends to calculate the emf. But when you have unequal concentrations you calculate the emf with the half reactions at both ends in addition to using the Nernst equation, where Q in the equation is [Anode]/[Cathode]?

Not exactly. Look at the Nerst equation again, only if both concentrations are 1 M can you just calculate E^ocell with the half reactions.

What would happen here if [Ni²⁺] and [Cr³⁺] are both 0.1M?

3Ni²⁺(aq)  +  2 Cr(s)  --> 3 Ni(s)  +  2Cr³⁺(aq)

[Ai]

When you have equal concentrations then you simple use the half reactions of both ends to calculate the emf. But when you have unequal concentrations you calculate the emf with the half reactions at both ends in addition to using the Nernst equation, where Q in the equation is [Anode]/[Cathode]?

Not exactly. Look at the Nerst equation again, only if both concentrations are 1 M can you just calculate E^ocell with the half reactions.

What would happen here if [Ni²⁺] and [Cr³⁺] are both 0.1M?

3Ni²⁺(aq)  +  2 Cr(s)  --> 3 Ni(s)  +  2Cr³⁺(aq)

What you are saying is that when both are at 1M only then I can use the half reactions to get E^o. But for any other concentrations we have to use the the Nerst Equation?

[LQ43]

Yes. What does Q represent in the Nerst equation? It is not just the half reactions of [Anode]/[cathode].

Can you determine why Q is not equal to 1 for this example?

If [Ni²⁺] and [Cr³⁺] are both 0.1M?

3Ni²⁺(aq)  +  2 Cr(s)  --> 3 Ni(s)  +  2Cr³⁺(aq)