Question

The chemical reactions taking place during discharge in a lead storage battery are $$ \begin{gathered} \mathrm{Pb}+\mathrm{SO}^{-} \longrightarrow \mathrm{PbSO}_{4} \\ \mathrm{PbO}_{2}+\mathrm{SO}_{4}^{2}+4 \mathrm{H}^{+} \longrightarrow \mathrm{PbSO}_{4}+2 \mathrm{H}_{4} \mathrm{O} \end{gathered} $$ (a) Complete each half-reaction by supplying electrons. (b) Which reaction is oxidation, and which is reduction? (c) Which reaction occurs at the anode of the battery?

Short answer

Oxidation: \( \text{Pb} + \text{SO}_{4}^{2-} \rightarrow \text{PbSO}_4 + 2e^- \)Reduction: \( \text{PbO}_2 + 4\text{H}^+ + \text{SO}_{4}^{2-} + 2e^- \rightarrow \text{PbSO}_4 + 2\text{H}_2\text{O} \)Anode reaction: \( \text{Pb} + \text{SO}_{4}^{2-} \rightarrow \text{PbSO}_4 + 2e^- \)

Step-by-step solution

Complete the half-reactions by supplying electrons

First, separate the overall reactions into their oxidation and reduction half-reactions.For the lead reaction: \( \text{Pb} + \text{SO}_{4}^{2-} \rightarrow \text{PbSO}_4 \)We balance the reaction by adding 2 electrons to the reactants:\( \text{Pb} + \text{SO}_{4}^{2-} \rightarrow \text{PbSO}_4 + 2e^- \)This is the oxidation half-reaction.For the lead dioxide reaction:\( \text{PbO}_2 + 4\text{H}^+ + \text{SO}_{4}^{2-} \rightarrow \text{PbSO}_4 + 2\text{H}_2\text{O} \)We balance the reaction by adding 2 electrons to the products:\( \text{PbO}_2 + 4\text{H}^+ + \text{SO}_{4}^{2-} + 2e^- \rightarrow \text{PbSO}_4 + 2\text{H}_2\text{O} \)This is the reduction half-reaction.

Identify which reaction is oxidation and which is reduction

Oxidation involves the loss of electrons, while reduction involves the gain of electrons.- The reaction \( \text{Pb} + \text{SO}_{4}^{2-} \rightarrow \text{PbSO}_4 + 2e^- \) is the oxidation half-reaction because it involves the loss of electrons.- The reaction \( \text{PbO}_2 + 4\text{H}^+ + \text{SO}_{4}^{2-} + 2e^- \rightarrow \text{PbSO}_4 + 2\text{H}_2\text{O} \) is the reduction half-reaction because it involves the gain of electrons.

Determine which reaction occurs at the anode of the battery

In a battery, oxidation occurs at the anode, while reduction occurs at the cathode.Since the oxidation reaction is \( \text{Pb} + \text{SO}_{4}^{2-} \rightarrow \text{PbSO}_4 + 2e^- \), this reaction occurs at the anode.

Key concepts

Electrochemical Cell

An electrochemical cell is a device that generates electrical energy from chemical reactions or facilitates chemical reactions through the introduction of electrical energy. It consists of two different conductors known as electrodes, immersed in electrolytes. These electrodes are the anode and the cathode. In a lead storage battery, a type of electrochemical cell, chemical reactions between the lead and sulfuric acid generate electrical energy, allowing the battery to power devices.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, also known as redox reactions, involve the transfer of electrons between two substances. In these reactions, oxidation is the process where a substance loses electrons, and reduction is where a substance gains electrons. For example, in the lead storage battery, the lead (Pb) undergoes oxidation by losing electrons, while lead dioxide (PbO₂) undergoes reduction by gaining electrons. Understanding how these reactions work is crucial for comprehending how energy is stored and released in batteries.

Half-Reactions

Half-reactions are the two parts of a redox reaction, representing the oxidation and reduction processes separately. This separation helps to understand the electron flow between substances. In the lead storage battery during discharge, the half-reactions are as follows:

Oxidation half-reaction:
\( \text{Pb} + \text{SO}_{4}^{2-} \rightarrow \text{PbSO}_4 + 2e^- \)

Reduction half-reaction:
\( \text{PbO}_2 + 4\text{H}^+ + \text{SO}_{4}^{2-} + 2e^- \rightarrow \text{PbSO}_4 + 2\text{H}_2\text{O} \)

These equations demonstrate the detailed steps in which the lead loses electrons and the lead dioxide gains electrons.

Battery Anode and Cathode

In an electrochemical cell like a lead storage battery, the anode and cathode are the two electrodes where oxidation and reduction reactions take place, respectively. The anode is where the oxidation reaction occurs, characterized by a loss of electrons. The cathode is where the reduction reaction takes place, which involves a gain of electrons. In the case of a lead storage battery:

• Anode: Lead (Pb) undergoes oxidation and releases electrons.
• Cathode: Lead dioxide (PbO₂) undergoes reduction and gains electrons.

This division into anode and cathode is essential for understanding how batteries work to store and release electrical energy.