Definitions

• Electrochemical Cell (Galvanic/Voltaic Cell): This is a device that converts the chemical energy of spontaneous redox reactions into electrical energy. Example: Daniel cell.
• Electrolytic Cell: This is a device that uses electrical energy to drive non-spontaneous redox reactions. Example: Electrolysis of molten sodium chloride.

Construction of Daniel Cell

Daniel cell is a specific type of Galvanic cell designed to convert the chemical energy of the zinc-copper redox reaction into electrical energy.

1. Anode Half-Cell: A zinc rod immersed in a solution of zinc sulfate ($ZnSO_4$). Oxidation occurs here.
2. Cathode Half-Cell: A copper rod immersed in a solution of copper sulfate ($CuSO_4$). Reduction occurs here.
3. Salt Bridge: A U-shaped tube filled with an inert electrolyte (such as $KCl$ or $NH_4NO_3$) that connects the two solutions and maintains electrical neutrality.

Cell Representation

Daniel cell is typically represented as: $$Zn(s) | Zn^{2+}(aq) || Cu^{2+}(aq) | Cu(s)$$

Working and Chemical Reactions

• At Anode (Oxidation): Zinc metal loses two electrons to form zinc ions, which move into the solution. $$Zn(s) ightarrow Zn^{2+}(aq) + 2e^-$$
• At Cathode (Reduction): Copper ions in the solution gain two electrons to form copper metal, which deposits on the copper rod. $$Cu^{2+}(aq) + 2e^- ightarrow Cu(s)$$
• Overall Cell Reaction: Combining the two half-reactions: $$Zn(s) + Cu^{2+}(aq) ightarrow Zn^{2+}(aq) + Cu(s)$$

As electrons flow from the zinc rod to the copper rod through an external wire, an electric current is generated.