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