Electrochemistry · Nernst Equation

Concentration & Cell Potential

A cell's voltage isn't fixed at E° — it drifts with the ion concentrations. The Nernst equation E = E° − (2.303RT/nF)·log Q says: pile up reactant (Cu²⁺) and the cell pushes harder; pile up product (Zn²⁺) and it weakens. Follow the line for the Daniell cell (Zn│Zn²⁺ ‖ Cu²⁺│Cu, E° = 1.10 V, n = 2).

line: E vs log Q Q = [Zn²⁺] / [Cu²⁺] pivot at log Q = 0 where E = E°

Conditions

[Cu²⁺] cathode · reactant 1.00 M
[Zn²⁺] anode · product 1.00 M
Temperature T 298 K
1.10 V
cell potential E
1.0
reaction quotient Q
0.00
log Q
0.0296
2.303RT/nF (V)
1.10
E° standard (V)
E = E° − slope·log Q

Try this

Dilute the product: drop [Zn²⁺] to 0.001 M while keeping [Cu²⁺] at 1 M — Q falls below 1, log Q goes negative and E rises above 1.10 V. Now do the reverse. Then raise T: the line pivots about log Q = 0, so temperature only matters when the cell is away from standard conditions.