Exploring Galvanic Cells: Examples and Calculations

What is a Galvanic Cell?

A galvanic cell, also known as a voltaic cell, is an electrochemical cell that converts chemical energy into electrical energy through spontaneous redox reactions. It consists of two electrodes: an anode (negative electrode) and a cathode (positive electrode), immersed in an electrolyte solution.

Key Components

• Anode: Where oxidation occurs (loss of electrons).
• Cathode: Where reduction occurs (gain of electrons).
• Electrolyte: The medium that allows ions to move between the anode and cathode.

Example 1: Zinc-Copper Galvanic Cell

Setup

In this example, we will consider a galvanic cell consisting of a zinc electrode in a zinc sulfate solution and a copper electrode in a copper sulfate solution.

Half-Reactions

• Anode (Oxidation):

  Zn(s) → Zn²⁺(aq) + 2e⁻

• Cathode (Reduction):

  Cu²⁺(aq) + 2e⁻ → Cu(s)

Cell Potential Calculation

To calculate the cell potential (E°) of the galvanic cell, we will use the standard reduction potentials from a table:

• Standard reduction potential for Cu²⁺/Cu = +0.34 V
• Standard reduction potential for Zn²⁺/Zn = -0.76 V

The cell potential is calculated as follows:

E° = E°(cathode) - E°(anode)
E° = (+0.34 V) - (-0.76 V)
E° = +1.10 V

Conclusion

This galvanic cell has a standard cell potential of +1.10 V, indicating a spontaneous reaction.

Example 2: Lead-Acid Battery

Setup

A common example of a galvanic cell is the lead-acid battery, which consists of lead dioxide (PbO₂) as the positive electrode and sponge lead (Pb) as the negative electrode, with sulfuric acid (H₂SO₄) as the electrolyte.

Half-Reactions

• Anode (Oxidation):

  Pb(s) + SO₄²⁻(aq) → PbSO₄(s) + 2e⁻

• Cathode (Reduction):

  PbO₂(s) + 3H⁺(aq) + SO₄²⁻(aq) + 2e⁻ → PbSO₄(s) + 2H₂O(l)

Cell Potential Calculation

Using standard reduction potentials:

• Standard reduction potential for PbO₂/Pb²⁺ = +1.46 V
• Standard reduction potential for Pb²⁺/Pb = -0.13 V

The cell potential is calculated as:

E° = E°(cathode) - E°(anode)
E° = (+1.46 V) - (-0.13 V)
E° = +1.59 V

Conclusion

The lead-acid battery has a standard cell potential of +1.59 V, showcasing its effectiveness in providing electrical energy.

Summary

Understanding galvanic cells involves recognizing their components, how they function, and the methods to calculate their cell potential. By studying practical examples such as the zinc-copper cell and the lead-acid battery, you can gain insights into the principles of electrochemistry and their applications in real-world scenarios.