What is the correct coefficient for O_2 needed to balance the chemical equation: C_3H_8 + O_2 → 3CO_2 + 4H_2O?

• A. 5
• B. 4
• C. 3
• D. 2

Answer: (A)

Verified step by step guidance

1. Identify the number of carbon (C) atoms in the reactant C_3H_8. Since there are 3 carbon atoms, you need 3 CO_2 molecules on the product side to balance carbon atoms.
2. Identify the number of hydrogen (H) atoms in the reactant C_3H_8. There are 8 hydrogen atoms, so you need 4 H_2O molecules on the product side to balance hydrogen atoms (because each H_2O has 2 hydrogen atoms).
3. Balance the oxygen (O) atoms by counting the total oxygen atoms on the product side. Each CO_2 has 2 oxygen atoms and each H_2O has 1 oxygen atom, so calculate total oxygen atoms as (3 × 2) + (4 × 1).
4. Since oxygen gas (O_2) is diatomic, divide the total oxygen atoms needed by 2 to find the coefficient for O_2 on the reactant side.
5. Write the balanced equation with the coefficients: C_3H_8 + (calculated coefficient) O_2 → 3 CO_2 + 4 H_2O, ensuring all atoms are balanced.