Question

Write the anode and cathode reactions and the overall cell reaction occurring in a lead storage battery during its use.

Hint:

In a lead-acid battery, lead sulfate is formed at both electrodes during discharge, and the reaction is reversible during charging.

Answer 1

To solve the problem, we need to write the anode and cathode reactions and the overall cell reaction occurring in a lead storage battery during its use.

1. Understanding the Lead Storage Battery:
A lead storage battery, commonly known as a lead-acid battery, consists of two lead (Pb) electrodes: a lead dioxide (PbO₂) cathode and a sponge lead (Pb) anode, immersed in a sulfuric acid (H₂SO₄) solution as the electrolyte.

2. Anode Reaction:
The anode in a lead storage battery consists of spongy lead (Pb). During discharge (when the battery is providing power), lead at the anode reacts with the sulfate ions (SO₄²⁻) from the sulfuric acid electrolyte to form lead sulfate (PbSO₄) and release two electrons. The anode reaction is: \[ \text{Pb}(s) + \text{SO₄}^{2-} (aq) \rightarrow \text{PbSO₄}(s) + 2e^- \]

3. Cathode Reaction:
The cathode in a lead storage battery consists of lead dioxide (PbO₂). During discharge, lead dioxide reacts with hydrogen ions (H⁺) from the sulfuric acid to form lead sulfate (PbSO₄) and water (H₂O), while accepting electrons. The cathode reaction is: \[ \text{PbO₂}(s) + 4H^+ (aq) + 2e^- \rightarrow \text{PbSO₄}(s) + 2H₂O (l) \]

4. Overall Cell Reaction:
The overall cell reaction is the sum of the anode and cathode reactions. Adding the two reactions together, the lead (Pb) and lead dioxide (PbO₂) react with sulfuric acid to form lead sulfate (PbSO₄) and water. The overall reaction is: \[ \text{Pb}(s) + \text{PbO₂}(s) + 2\text{H₂SO₄}(aq) \rightarrow 2\text{PbSO₄}(s) + 2\text{H₂O}(l) \]

5. Final Answer:
The anode reaction is: \[ \text{Pb}(s) + \text{SO₄}^{2-} (aq) \rightarrow \text{PbSO₄}(s) + 2e^- \] The cathode reaction is: \[ \text{PbO₂}(s) + 4H^+ (aq) + 2e^- \rightarrow \text{PbSO₄}(s) + 2H₂O (l) \] The overall cell reaction is: \[ \text{Pb}(s) + \text{PbO₂}(s) + 2\text{H₂SO₄}(aq) \rightarrow 2\text{PbSO₄}(s) + 2\text{H₂O}(l) \] During discharge, the battery releases energy as the lead plates are converted into lead sulfate.