Q.For the spontaneous reaction $\text{Zn}(s) + \text{Cu}^{2+}(aq) \to \text{Zn}^{2+}(aq) + \text{Cu}(s)$ that drives a Daniell cell, identify

A galvanic cell (also called a voltaic cell) is a device that converts the chemical energy of a spontaneous redox reaction directly into electrical energy. It is built from two half-cells, each consisting of a metal electrode dipped in a solution of its own ions, joined externally by a wire (through which electrons flow) and internally by a salt bridge (through which ions flow to keep both half-cell solutions electrically neutral).

The oxidation half-reaction (electron loss) always occurs at the anode, which is the negative terminal of a galvanic cell, since electrons accumulate there and flow out into the external circuit. The reduction half-reaction (electron gain) always occurs at the cathode, the positive terminal, which draws electrons in from the external circuit. In the classic Daniell cell, zinc metal is oxidized at the anode ($\text{Zn} \to \text{Zn}^{2+} + 2e^{-}$) and copper ions are reduced at the cathode ($\text{Cu}^{2+} + 2e^{-} \to \text{Cu}$), and the difference in electrical potential between the two electrodes drives a measurable current through the external circuit.

Without the salt bridge, charge would rapidly build up in each half-cell (positive charge accumulating in the anode compartment as $\text{Zn}^{2+}$ forms, negative charge effectively left behind in the cathode compartment as $\text{Cu}^{2+}$ is consumed), which would very quickly stop the reaction. The salt bridge allows spectator ions to migrate in the right direction to neutralize this buildup, keeping the cell functioning as long as the electrode materials and solution ions last.