CBSE · Class 12 · Chemistry · ElectrochemistryWhat is a Galvanic Cell? Explain its working mechanism by taking Daniel cell as a standard example. Also, write down the overall cell reaction and explain the origin of cell potential.

Galvanic Cell

\nA Galvanic cell (or voltaic cell) is an electrochemical device that converts chemical energy released during a spontaneous redox reaction into electrical energy. A classic example of a galvanic cell is the Daniel cell.

Construction and Working of Daniel Cell

1. Half-Cells and Electrodes:

   • Oxidation Half-Cell (Anode): A zinc rod is dipped in a solution of zinc sulfate ($\text{ZnSO}_4$). Oxidation takes place here: $\text{Zn}(s) \rightarrow \text{Zn}^{2+}(aq) + 2e^-$. Since electrons are released, the zinc electrode acts as the negative pole.
   • Reduction Half-Cell (Cathode): A copper rod is dipped in a solution of copper sulfate ($\text{CuSO}_4$). Reduction takes place here: $\text{Cu}^{2+}(aq) + 2e^- \rightarrow \text{Cu}(s)$. Since electrons are consumed, the copper electrode acts as the positive pole.

2. Salt Bridge and Its Function:

   • A salt bridge (an inverted U-tube containing an inert electrolyte like $\text{KCl}$ or $\text{K}_+\text{NO}_3^-$ in agar-agar gel) connects the two half-solutions.
   • It completes the electrical circuit and maintains electrical neutrality in both half-cells by preventing the accumulation of net positive or negative charges.

Overall Cell Reaction

• Anode reaction: $\text{Zn}(s) \rightarrow \text{Zn}^{2+}(aq) + 2e^-$
• Cathode reaction: $\text{Cu}^{2+}(aq) + 2e^- \rightarrow \text{Cu}(s)$
• Overall reaction: $\text{Zn}(s) + \text{Cu}^{2+}(aq) \rightarrow \text{Zn}^{2+}(aq) + \text{Cu}(s)$

Origin of Cell Potential\nThe potential difference between the two electrodes of a galvanic cell is caused by the difference in their tendency to lose or gain electrons. When the circuit is closed, electrons flow from the zinc electrode to the copper electrode due to this potential difference, generating an electric current.