Final answer:
The cell potential may change if the temperature or concentrations of the reactant and product ions change. The Nernst equation can be used to calculate the cell potential. As the concentrations change, the value of the reaction quotient (Q) changes, leading to a change in cell potential.
Step-by-step explanation:
The cell potential, measured in volts (V), may change if the temperature changes or if the concentrations of the reactant and product ions change. This relationship is summarized by the Nernst equation:
Ecell = Eºcell - (0.0592/n) * log(Q)
Where Ecell is the cell potential, Eºcell is the standard cell potential, n is the number of electrons transferred in the balanced equation, and Q is the reaction quotient.
As the concentrations of the reactant and product ions change, the value of Q changes. When the value of Q is less than 1, the cell potential is greater than Eºcell. As Q approaches 1, the cell potential decreases and eventually reaches Eºcell when Q equals 1. Beyond this point, the cell potential continues to decrease as Q increases further.
For example, in a Zn/Cu cell with initial concentrations of 1.0 M Cu²+ and 1.0 × 10^-6 M Zn²+, the initial voltage is greater than Eºcell because Q < 1. As the reaction progresses, [Zn²+] increases while [Cu²+] decreases, leading to an increase in Q and a decrease in cell potential. When the concentrations in the two compartments are the opposite of the initial concentrations, Q = 1.0 × 10^6, and the cell potential is reduced to 0.92 V.