Voltaic Cells

Introduction

• Redox reactions involve the transfer of electrons from one species to another.
• Spontaneous redox reactions release energy which can be harnessed to do work.
• To capture this energy, the reaction is divided into two half-reactions: oxidation and reduction.
• Voltaic/Galvanic Cell is created by separating these reactions into different containers and connecting them with a wire.

Voltaic Cell Structure

• Half-cells: Each half-cell contains a metal electrode and a solution with metal ions.
• Electrodes: Strips of metal where reactions occur. Two types of electrodes:
  • Anode: Site of oxidation (loss of electrons).
  • Cathode: Site of reduction (gain of electrons).
• Salt Bridge: Contains an electrolyte solution to maintain electrical neutrality and allow ion flow.

How Voltaic Cells Work

• Electrons flow from the anode (oxidation) to the cathode (reduction).
• Cell diagrams represent electrochemical cells, showing the arrangement of anodes, cathodes, and salt bridges.

Cell Diagram Conventions

• Anode on the left, cathode on the right.
• Salt bridge represented by ||.
• Phase changes represented by |.

Example Reactions and Cell Diagrams

1. Cu(aq)²⁺ + Ba(s) → Cu(s) + Ba(aq)²⁺

   • Anode: Ba(s) (oxidation)
   • Cathode: Cu(aq)²⁺ (reduction)
   • Cell Diagram: Ba²⁺(aq) | Ba(s) || Cu(s) | Cu²⁺(aq)

2. 2Al(s) + 3Sn(aq)²⁺ → 2Al(aq)³⁺ + 3Sn(s)

   • Anode: Al(s) (oxidation)
   • Cathode: Sn(aq)²⁺ (reduction)
   • Cell Diagram: Al(s) | Al³⁺(aq) || Sn²⁺(aq) | Sn(s)

Cell Voltage/Cell Potential

• Cell Voltage: Difference in potential between the two half-cells, measured with a voltmeter.
• Standard Cell Potential (E°cell): Calculated as E°cathode - E°anode.
• A positive E°cell indicates a spontaneous reaction (voltaic cell), while a negative E°cell implies a non-spontaneous reaction (electrolytic cell).

Key Terms

• OIL RIG acronym for remembering redox reactions:
  • OIL: Oxidation Is Loss (of electrons).
  • RIG: Reduction Is Gain (of electrons).

Importance of Salt Bridges

• Maintains electrical neutrality and allows continuous flow of the electrochemical reaction, preventing charge buildup around electrodes.

References

• Several chemistry textbooks and publications as sources for deeper exploration of electrochemistry and voltaic cells.

Contributors

• Shamsher Singh, Deborah Gho