Standard Electrode Potential

Definition of Electrode Potential

• Potential difference produced when equilibrium is established between metal ( M ) and its aqueous ions ( M^{n+} ) in a half-cell.

Electrode Potential of a Cell

• Cannot be measured directly.
• Determined by the difference in electrode potential between two half-cells.
• Measured by pairing with a standard reference electrode system, internationally recognized as the standard hydrogen electrode.

Standard Hydrogen Electrode

• Function of PtO₂: Increases surface area of Pt to adsorb ( H_2 ).
  • Brings ( H_2 ) molecules closer to ( H^+ ) ions in solution.
• Half Equation: [ 2H^+ (\text{aq}) + 2e^- \rightarrow H_2 (\text{g}) ]
• Standard electrode potential, ( E^0 ): [ H^+ (\text{aq}) + e^- \rightarrow \frac{1}{2}H_2 (\text{g}), \quad E^0 = 0.00 \text{ V} ]

Standard Electrode Potential Value, ( E )

• Apparatus set-up to determine ( E ) of Zinc.
• With standard hydrogen potential at 0.00 V, voltmeter reads 0.76 V for zinc.
  • Zinc ( Zn ) has a greater tendency to release electrons than hydrogen.
  • Thus, Zn becomes the negative terminal; electrons flow from Zn (negative) to Pt (positive).

Electrode Comparison

• Zinc: Negative Terminal
  • Half Equation: [ Zn(s) \rightarrow Zn^{2+} (\text{aq}) + 2e^-, \quad E^0 = 0.76 \text{ V} ]
  • Reaction: Oxidation
• Hydrogen: Positive Terminal
  • Reaction: Reduction

Oxidizing and Reducing Agents

• Standard electrode potential ( E ) is also called the standard reduction potential.
• ( E ) value indicates the tendency to accept/donate electrons.

Standard Electrode Potential Series

• Used to determine the strength of oxidizing or reducing agents.
• Ag and Mg Comparison:
  • Ag more positive ( E ): Stronger oxidizing agent, easier electron acceptance, harder electron release.
  • Mg more negative ( E ): Stronger reducing agent, easier electron release, harder electron acceptance.

Relationship of ( E ) to Strength

• More positive or less negative ( E ): stronger oxidizing agent, easier reduction.
• More negative or less positive ( E ): stronger reducing agent, easier oxidation.

Related Topics

• Redox Reaction
• Voltaic Cell
• Electrolytic Cell
• Extraction of Metals
• Rusting
• Types of Carbon Compounds
• Homologous Series
• Chemical Properties
• Isomerism
• Heat Change in Reactions

Chapter: Redox Equilibrium
Topic: Standard Electrode Potential
Form: 5 Chemistry