2 C2H6 + 7 O2 → 4 CO2 + 6 H2O

Question

201.6 g C2H6 reacts with 400.0g O2 to make water..
What is the mass of H2O based on the above reactant amounts?

Answer 1

This is a limiting reagent (LR) problem. You know that when the amount is given for more than one reactant in the equation.
2 C2H6 + 7 O2 → 4 CO2 + 6 H2O
mols C2H6 = grams/molar mass = 201.6/30 = approx 6.7 but you need to recalculate this AND ALL OF THE OTHERS SINCE I'VE JUST DONE ESTIMATES.
How much H2O would this form? That's mols C2H6 x (6 mols H2O/2 mol C2H6) = about 6.7 x 3 = 20
mols O2 = 400/32 = 12. How much water would that form? That's
12 mols O2 x (6 mols H2O/7 mols O2) = 11
In LR problems the small number wins ; therefore, O2 is the LR and approx 11 mols H2O will be formed. Convert that to grams.
grams H2O = mols H2O x molar mass H2O = ?