Redox Reactions Overview

Overview

This lecture introduces redox reactions, explains how to determine oxidation and reduction using different concepts, and defines key terms including oxidizing and reducing agents.

Concepts of Redox Reactions

• Redox reactions involve the transfer of electrons, oxygen, or hydrogen, and/or changes in oxidation numbers.
• LEO GER: "Losing Electrons is Oxidation" (LEO) and "Gaining Electrons is Reduction" (GER).

Oxygen Transfer Concept

• Oxidation: a substance gains oxygen.
• Reduction: a substance loses oxygen.
• Example: Fe₂O₃ losing oxygen is reduction; CO forming CO₂ by gaining oxygen is oxidation.

Hydrogen Transfer Concept

• Oxidation: losing hydrogen atoms.
• Reduction: gaining hydrogen atoms.
• Example: Ethanol oxidized to ethene (loses hydrogen); ethene reduced to ethanol (gains hydrogen).

Electron Transfer Concept

• Oxidation: loss of electrons by a substance.
• Reduction: gain of electrons by a substance.
• Both steps occur together in a redox reaction.

Oxidation Number Concept

• Oxidation: increase in oxidation number.
• Reduction: decrease in oxidation number.
• Example: Mg (0) to Mg²⁺ (+2) is oxidation; H⁺ (+1) to H₂ (0) is reduction.

Spectator Ions

• Ions whose oxidation states do not change during the reaction are called spectator ions.

Disproportionation Reactions

• A single element undergoes both oxidation and reduction in the same reaction.
• Example: O₂²⁻ (peroxide) to O₂ and H₂O, or Br₂ to Br⁻ and BrO₃⁻.

Oxidizing and Reducing Agents

• Oxidizing agent: substance that causes oxidation by undergoing reduction itself.
• Reducing agent: substance that causes reduction by undergoing oxidation itself.
• Example: Fe₂O₃ as oxidizing agent, CO as reducing agent.

Key Terms & Definitions

• Oxidation — process involving loss of electrons, gain of oxygen, or increase in oxidation number.
• Reduction — process involving gain of electrons, loss of oxygen, or decrease in oxidation number.
• Redox Reaction — chemical reaction involving both oxidation and reduction.
• Spectator Ion — ion that does not change oxidation state during reaction.
• Disproportionation — reaction where an element is both oxidized and reduced.
• Oxidizing Agent — substance reduced in a redox reaction that oxidizes another substance.
• Reducing Agent — substance oxidized in a redox reaction that reduces another substance.

Action Items / Next Steps

• Review example redox equations and identify oxidation numbers.
• Practice identifying oxidizing and reducing agents in sample reactions.