Galvanic Cells

Chemistry: IB Diploma Higher Level, topic 6.7.2

Electrochemical cells in which a thermodynamically favored redox reaction takes place are called galvanic cells.

A galvanic cell based on the spontaneous reaction between copper and silver(I) is depicted in the image above and repeated on the next slide.
The cell is comprised of two half-cells, each containing the redox conjugate pair (“couple”) of a single reactant.
The half-cell shown at the left contains the Cu(0)/Cu(II) couple in the form of a solid copper foil and an aqueous solution of copper nitrate.
The right half-cell contains the Ag(I)/Ag(0) couple as solid silver foil and an aqueous silver nitrate solution.

The anode of an electrochemical cell is the electrode at which oxidation occurs (in this case, the Cu foil).
The cathode is the electrode where reduction occurs (the Ag foil).
The redox reactions in a galvanic cell occur only at the interface between each half-cell’s reaction mixture and its electrode.
To keep the reactants separate while maintaining charge-balance, the two half-cell solutions are connected by a tube filled with inert electrolyte solution called a salt bridge.

The thermodynamically favorable reaction in this cell:
Produces Cu²⁺ cations in the anode half-cell.
Consumes Ag⁺ ions in the cathode half-cell.
This results in a compensatory flow of inert ions from the salt bridge that maintains charge balance.
Increasing concentrations of Cu²⁺ in the anode half-cell are balanced by an influx of NO₃₋ from the salt bridge.
A flow of Na⁺ into the cathode half-cell compensates for the decreasing Ag⁺ concentration.

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