Galvanic Cells

Introduction

• In principle, any spontaneous redox reaction can serve as a source of electrical energy in a galvanic cell. 
    * This cell is designed to take advantage of the movement of electrons, which occurs during a redox reaction. 
    * The oxidation and reduction half reactions are compartmentalized into half-cells.
      * Anode: site of oxidation
        * Anions flow to the anode
      * Cathode: site of reduction
        * Cations flow to the cathode
      * Electrons move through an external wire from the anode to the cathode. 
        * These “moving” electrons can be used as a source of electrical energy. 

Charge Balance

• As the oxidation occurs, a surplus of positive ions builds up at the anode.
• The area near the cathode becomes deficient in positive ions.
• Salt bridge: supplies additional cations and anions needed to balance out these charge differences and complete the circuit. 
• The salt bridge is a porous material consisting of a concentrated salt solution.
    * Anions flow toward the anode to neutralize the build-up of positive charge. 
    * Cations flow toward the cathode to “replace” the cations that are being consumed. 
    * This flow of ions enables electrical neutrality to be achieved, the circuit to be complete, and current to flow

Cell Notation

• Describes what happens in a galvanic cell.
• Oxidation on the left
• Reduction on the right
• Single vertical line represents a phase boundary
    * Liquid-metal or liquid-gas, etc.
• Double line is the salt bridge
• Don’t include spectator ions
• Sometimes the concentration of the ion(s) is included.