Question

The chemical equation below shows the combustion of propane (C3H8).

C3H8 + 5O2 mc012-1.jpg 3CO2 + 4H2O

The molar mass of oxygen gas (O2) is 32.00 g/mol. The molar mass of C3H8 is 44.1 g/mol. What mass of O2, in grams, is required to completely react with 0.025 g C3H8?

Answer 1

The balanced equation for the reaction is
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

Moles (mol) = mass (g) / molar mass (g/mol)

Mass of the C₃H₈ = 0.025 g
Molar mass of C₃H₈ = 44.1 g/mol
Hence, moles of C₃H₈ = 0.025 g / 44.1 g/mol = 5.67 x 10⁻⁴ mol

The stoichiometric ratio between C₃H₈ and O₂ is 1 : 5.

Hence, moles of O₂ = moles of C₃H₈ x 5
= 5.67 x 10⁻⁴ mol x 5
= 2.835 x 10⁻³ mol

Molar mass of O₂ = 32.00 g/mol
Hence, mass of O₂ = moles x molar mass
= 2.835 x 10⁻³ mol x 32.00 g/mol
= 0.09072 g

Hence, needed O₂ for the reaction is 0.09072 g.