Question

What mass of octane must be burned in order to liberate 5510 kJ of heat? ΔHcomb = -5471 kJ/mol.

Answer 1

2C8H18 + 17O2 ==>16CO2 + 18H2O
So you have 5471 kJ for 1 mole (which is 114.23 grams); therefore,
2*molar mass C8H18 x (5510/5471) = ??

Answer 2

228.46 / (5510/5471) = 226.84