Volume of gases?

Question

Propane, C3H8, is a hydrocarbon that is commonly used as fuel for cooking.

a. Calculate the volume of air at 30 degrees C and 1.00 atmosphere that is needed to burn completely 10.0 grams of propane. Assume that air is 21.0 percent O2 by volume.

Answer 1

5O2 + C3H8 => 3CO2 + 4H2O

the moles of propane : 10 / 44 =0.227 moles
the moles of O2 needed 0.227 * 5 = 1.135 moles
the volume of O2 : V = nRT / P = 1.135 * 0.082 * (30 + 273) / 1 = 28.2L
the volume of air : 28.2 * 100 / 21 = 134.29 litres