chemistry stoichiometry

Question

combustion of C5H12 produced 34.2 L of water vapor at 25 degrees celsius and 725 mm Hg. how many grams of C5H12 reacted ?

Answer 1

C₅H₁₂ + 8O₂ ==> 5CO₂(g) + 6H₂O(g) .. balanced equation for combustion of pentane

moles of H2O produced: PV = nRT

n = PV / RT = (725 mm Hg)(34.2 L) / (62.36 LmmHg/Kmol)(298K)

n = 1.33 mols H2O vapor

grams C₅H₁₂ used = 1.33 mols H2O x 1 mol C₅H₁₂ / 6 mols H2O x 72 g C₅H₁₂ / mol = 16.0 g C₅H₁₂