Redox Reactions Lecture Notes

Introduction to Redox Reactions

• Redox reactions involve a change in oxidation numbers of elements.
• To identify a redox reaction, assign oxidation numbers and check for changes.

Mnemonic for Redox Reactions

• LEO the Lion says GUR:
  • LEO: Loss of Electrons is Oxidation
  • GUR: Gain of Electrons is Reduction
• Oxidation: Increase in oxidation number (both start with vowels).
• Reduction: Decrease in oxidation number (both start with consonants).

Types of Redox Reactions

Combustion Reaction

• Fuel is burned in the presence of an oxidant, usually generating heat and flame.
• Example: Combustion of Ethylene (C2H4 + O2 -> CO2 + H2O).
  • Always produces CO2 and H2O when organic fuel is burned.

Oxidation Numbers in Combustion

• Assign oxidation numbers:
  • Hydrogen in C2H4: +1
  • Carbon in C2H4: -2
  • Oxygen in O2: 0
• Changes observed:
  • Oxygen goes from 0 to -2 (reduction).
  • Carbon goes from -2 to +4 (oxidation).

Single Displacement Reaction

• An ion in solution is displaced or replaced via oxidation of a metallic element.
• Example: Silver nitrate and copper reaction.
  • AgNO3 + Cu -> Cu(NO3)2 + Ag

Oxidation Numbers in Single Displacement

• Copper changes from 0 to +2 (oxidation).
• Silver ions change from +1 to 0 (reduction).

Identifying Redox Reactions

Example 1: No Redox

• Zinc and carbon dioxide reaction:
  • No change in oxidation states of Zn, C, or O.

Example 2: Redox Reaction

• Gallium and bromine reaction:
  • Ga goes from 0 to +3 (oxidation).
  • Br goes from 0 to -1 (reduction).
• Oxidizing Agent: Bromine
• Reducing Agent: Gallium

Example 3: No Redox

• Barium chloride and potassium sulfate reaction:
  • No change in oxidation numbers.

Example 4: Disproportionation Reaction

• Hydrogen peroxide decomposition:
  • O in H2O2 goes from -1 to -2 (reduction) and -1 to 0 (oxidation).
• Peroxide is both the oxidizing and reducing agent.
• Special type of reaction: Disproportionation (same element is oxidized and reduced).