Lecture Notes on Reaction Rates and Ionic Equations

Importance of Ionic Equations

• Expressing and comparing reaction rates is best done by considering individual ions.
• Convert formula equations to ionic equations for clarity.

Example: Zinc and Hydrochloric Acid Reaction

• Reaction Description: Zinc in hydrochloric acid forms hydrogen gas and zinc chloride.
• Balanced Formula Equation:
  • Zn (s) + 2 HCl (aq) → H2 (g) + ZnCl2 (aq)
  • Aqueous solutions like 2 HCl and ZnCl2 dissociate into ions.

Dissociation into Ions

• HCl Dissociation:
  • HCl (aq) → 2 H⁺ (aq) + 2 Cl⁻ (aq)
• ZnCl2 Dissociation:
  • ZnCl2 (aq) → Zn²⁺ (aq) + 2 Cl⁻ (aq)
• Solid and gaseous species remain unchanged.

Complete Ionic Equation

• Displays all ions in aqueous solutions; solids and gases remain in molecular form.
• Spectator Ions: Ions that do not change or participate in the reaction, e.g., Cl⁻.

Net Ionic Equation

• Excludes spectator ions.
• Shows only species that react and products formed.
• Most useful for understanding reaction rates.

Comparison of Equation Types

• Formula Equation: Shows molecular formulas and states.
• Complete Ionic Equation: Shows all ions, including spectator ions.
• Net Ionic Equation: Shows only reacting species, excluding spectators.

Example: Aqueous Bromine and Iron Iodide Reaction

• Formula Equation:
  • Br2 (aq) + FeI3 (aq) → I2 (aq) + FeBr3 (aq)
• Ionic Compounds: FeI3 and FeBr3 dissociate into ions.
• Complete Ionic Equation:
  • 2 FeI3 (aq) → 2 Fe³⁺ (aq) + 6 I⁻ (aq)
  • 2 FeBr3 (aq) → 2 Fe³⁺ (aq) + 6 Br⁻ (aq)
  • Br2 and I2 remain in molecular form.
• Spectator Ion: Fe³⁺ is identical on both sides.
• Net Ionic Equation: Excludes Fe³⁺ spectator ions.

Summary

• Formula Equation: Molecular form, states shown.
• Complete Ionic Equation: All ions, including spectators.
• Net Ionic Equation: Reacting species only, no spectators.