Lecture on Chemical Equation Balancing

Introduction

• The lecture covers balancing chemical equations.
• Three examples are provided for practice.

Example 1: Water Decomposition

• Equation: H2O (liquid) → H2 (gas) + O2 (gas)
• Initial Count:
  • Left: 2 Hydrogens, 1 Oxygen
  • Right: 2 Hydrogens, 2 Oxygens
• Balancing Steps:
  1. Add coefficient of 2 to H2O to balance oxygens: 2 H2O → 2 H2 + O2
  2. New count:
     • Left: 4 Hydrogens, 2 Oxygens
     • Right: 4 Hydrogens, 2 Oxygens
• Conclusion: Equation balanced with coefficients 2 for H2O and H2.

Example 2: Formation of N2O5

• Equation: N2 (gas) + O2 (gas) → N2O5 (gas)
• Initial Count:
  • Left: 2 Nitrogens, 2 Oxygens
  • Right: 2 Nitrogens, 5 Oxygens
• Balancing Steps:
  1. Identify the least common multiple for oxygens: LCM of 2 and 5 is 10.
  2. Adjust coefficients to balance oxygens:
     • Left: 5 O2 gives 10 Oxygens
     • Right: 2 N2O5 gives 10 Oxygens
  3. Balance Nitrogens: Add 2 to N2 on the left
• Conclusion: Balanced equation with coefficients 2 for N2, 5 for O2, and 2 for N2O5.

Example 3: A Pre-balanced Equation

• Initial Observation:
  • Hydrogen: 1 on both sides
  • Chlorine: 1 on both sides
  • Sodium (Na): 1 on both sides
  • Oxygen: 1 on both sides
• Conclusion: Equation is already balanced.

Key Takeaways

• Always check if an equation is balanced before adding coefficients.
• Use least common multiples for complex balancing.
• Double-check work to ensure balance.
• Not all equations need adjustment: Some are balanced as initially given.