Given the balanced equation representing a reaction:
C3H8(g) + 5O2(g)==>3CO2(g) + 4H2O(g)
What is the total number of moles of O2(g) required for the complete combustion of 1.5 moles of C3H8(g)?
(1) 0.30 mol (3) 4.5 mol
(2) 1.5 mol (4) 7.5 mol
The answer is (4) 7.5 mol. The consuming of reactants has the same ratio as the balanced equation. So the ratio of consuming C3H8 and O2 is equal to 1:5. So when 1.5 mol of C3H8 consumed, 1.5*5=7.5 mol O2 consumed.
