chapter 5 electrochemistry class 12 chemistry textbook solution

4. Answer the following :

xi. What are anode and cathode for Leclanche’ dry cell ? Write electrode reactions and overall cell reaction when it generates electricity. 


Anode: The anode in a Leclanché dry cell is typically made of zinc (Zn). It serves as the site of the oxidation reaction, where zinc undergoes oxidation to release electrons.

Anode Reaction: Zn(s) → Zn²⁺(aq) + 2e⁻

Cathode: The cathode in a Leclanché dry cell is typically a porous carbon rod surrounded by a mixture of manganese dioxide (MnO₂) and powdered carbon, often with an electrolyte paste. The cathode plays a crucial role in the reduction reaction, where electrons are consumed.

Cathode Reaction: 2MnO₂(s) + 2NH₄⁺(aq) + 2e⁻ → Mn₂O₃(s) + 2NH₃(aq) + H₂O(l)

Overall Cell Reaction: The overall cell reaction for a Leclanché dry cell is the combination of the anode and cathode reactions. The cell operates in an aqueous electrolyte, usually containing ammonium chloride (NH₄Cl).

Overall Cell Reaction: Zn(s) + 2MnO₂(s) + 2NH₄⁺(aq) → Zn²⁺(aq) + Mn₂O₃(s) + 2NH₃(aq) + H₂O(l)

This chemical reaction generates an electric current as electrons flow from the anode to the cathode through an external circuit, allowing the cell to power electrical devices.

It's important to note that while the Leclanché cell has been widely used historically, it has been largely replaced by alkaline batteries in modern portable electronic devices due to their superior performance and longer lifespan.

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