Question

Lead-Acid Battery What substance is reduced in a lead-acid storage battery? What substance is oxidized? What substances are produced in each reaction?

Short answer

In a lead-acid storage battery, lead dioxide (PbO₂) is reduced and lead (Pb) is oxidized. The products formed in the reduction half-reaction are lead sulfate (PbSO₄) and water (H₂O), while the product formed in the oxidation half-reaction is lead sulfate (PbSO₄).

Step-by-step solution

Understand Lead-Acid Battery Components

A lead-acid battery consists of two types of electrodes (lead and lead dioxide) and an electrolyte (sulfuric acid). The overall electrochemical reaction happens in two separate half-reactions. In one half-reaction, a substance is reduced (gains electrons), while in the other half-reaction, a substance is oxidized (loses electrons).

Write the Half-Reaction Equations

For the reduction half-reaction, the lead dioxide (PbO₂) electrode is reduced by gaining electrons. The equation for this reaction is: \(PbO_2 + 4H^+ + SO_4^{2-} + 2e^- \rightarrow PbSO_4 + 2H_2O\) For the oxidation half-reaction, the lead (Pb) electrode is oxidized by losing electrons. The equation for this reaction is: \(Pb + SO_4^{2-} \rightarrow PbSO_4 + 2e^-\) Now that we have written the half-reaction equations, we can answer the questions in the exercise.

Identify the Reduced Substance

The substance that is reduced in a lead-acid battery is lead dioxide (PbO₂). This occurs in the reduction half-reaction, where it gains electrons.

Identify the Oxidized Substance

The substance that is oxidized in a lead-acid battery is lead (Pb). This occurs in the oxidation half-reaction, where it loses electrons.

Determine the Products of Each Reaction

For the reduction half-reaction, the products are lead sulfate (PbSO₄) and water (H₂O). For the oxidation half-reaction, the product is lead sulfate (PbSO₄). In conclusion, in a lead-acid storage battery, lead dioxide (PbO₂) is reduced and lead (Pb) is oxidized. The products formed in each reaction are lead sulfate (PbSO₄) and water (H₂O).

Key concepts

Electrochemical Reaction

The lead-acid battery is a common type of electrochemical cell that powers many devices, like cars and backup power systems. At its core, an electrochemical reaction converts chemical energy into electrical energy through a series of reactions involving electron transfer. This is achieved in two half-reactions. In a lead-acid battery, these reactions take place between the lead dioxide (PbO₂) and lead (Pb) electrodes with the sulfuric acid electrolyte.

• Energy conversion: Chemical to electrical.
• Involves electron transfer: Reduction and oxidation reactions.
• Main participants: Lead dioxide, lead, and sulfuric acid.

Understanding these reactions helps us to harness electrical energy from chemical processes and explains the functionality of these batteries in everyday usage.

Reduction Half-Reaction

The reduction half-reaction is one of the key processes in a lead-acid battery. In this reaction, the lead dioxide (PbO₂) electrode serves as the cathode, where reduction occurs as it gains electrons. The balanced equation for this reaction is:\[PbO_2 + 4H^+ + SO_4^{2-} + 2e^- \rightarrow PbSO_4 + 2H_2O\]

• Electrons are gained.
• Occurs at the cathode.
• Produces lead sulfate and water.

By understanding the reduction half-reaction, we learn how energy is stored in a battery. The gaining of electrons is fundamental to the transfer and conservation of energy.

Oxidation Half-Reaction

In the complementary process of the electrochemical reaction, oxidation occurs at the anode. For the lead-acid battery, the lead (Pb) electrode undergoes oxidation by losing electrons. The equation capturing this process is:\[Pb + SO_4^{2-} \rightarrow PbSO_4 + 2e^-\]

• Electrons are lost.
• Occurs at the anode.
• Forms lead sulfate.

This oxidation half-reaction is crucial as it is responsible for producing electrons that travel through the external circuit, resulting in the flow of electricity that powers devices.

Lead Dioxide Reduction

Lead dioxide reduction is a specific manifestation of the reduction half-reaction in lead-acid batteries. Here, lead dioxide ( PbO₂) is the substance that gains electrons, turning into lead sulfate and water as it accepts electrons from the circuit. The important things to remember about this process include:

• Lead dioxide acts as the oxidizing agent.
• Transforms into lead sulfate (PbSO₄) through reduction.
• Accompanied by the release of water (H₂O).

Understanding this reduction process provides insights into how the battery manages to move charged particles, thus creating the energy we use to power tools and machines.

Lead Oxidation

Lead oxidation in a lead-acid battery is another essential half-reaction that pairs with the process occurring at the cathode. In this reaction, lead (Pb) loses electrons and turns into lead sulfate (PbSO₄). This process is depicted by the equation:\[Pb + SO_4^{2-} \rightarrow PbSO_4 + 2e^-\]Key aspects of lead oxidation include:

• Lead acts as the reducing agent.
• Converts to lead sulfate (PbSO₄) upon oxidation.
• Provides electrons necessary for the external circuit.

The process of lead oxidation is integral to sustaining the electron flow in the battery, which in turn powers electrical devices by creating a steady stream of energy.