Balancing Chemical Equations: Combustion Reaction

Introduction

• Balancing chemical equations involves ensuring that the number of each type of atom on the reactant side equals the number on the product side.
• Focus is on a combustion reaction involving ethylene and oxygen.
• Ethylene [(C_2H_4)] reacts with dioxygen [(O_2)] to produce carbon dioxide [(CO_2)] and water [(H_2O)].

Strategy for Balancing Equations

• Step 1: Balance molecules with multiple elements first.
  • Complex molecules can affect more than one type of atom.
• Step 2: Balance molecules that are composed of only one type of atom last.
  • Typically, these are simpler to adjust last.

Process of Balancing

1. Balance Carbons

   • Count carbons (C) on both sides.
   • Start with ethylene which has 2 carbons.
   • Adjust CO2 on the product side to have 2 CO2 molecules to balance the carbons.

2. Balance Hydrogens

   • Count hydrogens (H).
   • Ethylene has 4 hydrogens.
   • Adjust water (H2O) molecules on the product side to have 2 water molecules to balance hydrogens.

3. Balance Oxygens

   • Leave oxygens (O) for last because they are present in multiple compounds.
   • Count oxygens on the product side:
     • 2 CO2 = 4 Oxygens
     • 2 H2O = 2 Oxygens
   • Total on product side: 6 oxygens.
   • On reactant side, need 3 O2 molecules to balance the oxygens.

Conclusion

• After adjusting coefficients:
  • 1 C2H4 + 3 O2 → 2 CO2 + 2 H2O
• This balanced equation reflects conservation of mass (atoms) in the reaction.
• Balancing equations is critical for understanding stoichiometry in chemical reactions.