C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
mole C₃H₈ = 68.5 : Mr C₃H₈ = 68.5 : 44 g/mol = 1.557
mole O₂ = 83.4 : Mr O₂ = 83.4 : 32 g/mol = 2.606
to find limiting reactants :
divide the number of moles by their respective coefficients, and the small quotient will be a limiting reactants
C₃H₈ : O₂ = 1.557/1 : 2.606/5 = 1.557 : 0.521
O₂ as a limiting reactant, C₃H₈ excess reactants
reacted mole of C₃H₈ : 1/5 x 2.606 = 0.5212
unreacted mole of C₃H₈ : 1.557 - 0.5212 = 1.0358
mass of C₃H₈ (unreacted) = 1.0358 x 44/gmol = 45.575 g