Write the balanced equation for the complete combustion of propane.

Write the balanced equation for the complete combustion of propane.

• A. C3H8 + O2 -> CO2 + H2O
• B. C3H8 + 5O2 -> 3CO2 + 4H2O
• C. C3H8 + 3O2 -> 3CO + 4H2O
• D. C3H8 + 4O2 -> 3CO2 + 4H2O

Answer: (B)

Balancing the equation by conserving atoms is the key. Propane has 3 carbon atoms and 8 hydrogen atoms. In complete combustion, all carbon ends up as carbon dioxide and all hydrogen as water, so you need 3 CO2 to store the 3 carbons and 4 H2O to store the 8 hydrogens (each water has 2 hydrogens). That gives 6 oxygens in CO2 and 4 oxygens in H2O, totaling 10 oxygens on the product side. Since each O2 molecule provides 2 oxygens, you need 5 O2 molecules. Put it all together: C3H8 + 5O2 -> 3CO2 + 4H2O. If there isn’t enough oxygen, you’d get CO or other products, which is incomplete combustion, and other options don’t balance the atoms correctly.

Balancing the equation by conserving atoms is the key. Propane has 3 carbon atoms and 8 hydrogen atoms. In complete combustion, all carbon ends up as carbon dioxide and all hydrogen as water, so you need 3 CO2 to store the 3 carbons and 4 H2O to store the 8 hydrogens (each water has 2 hydrogens). That gives 6 oxygens in CO2 and 4 oxygens in H2O, totaling 10 oxygens on the product side. Since each O2 molecule provides 2 oxygens, you need 5 O2 molecules. Put it all together: C3H8 + 5O2 -> 3CO2 + 4H2O. If there isn’t enough oxygen, you’d get CO or other products, which is incomplete combustion, and other options don’t balance the atoms correctly.