Why does burning 1 kg of gasoline produce more than 3kg of carbon dioxide?

1000g C8H18 (octane - approximately gasoline) =114 Mwt +12.5 O2 = 32 Mwt ----> 8 CO2 = 44 Mwt + 9H2O

1000/114 = 8.772 moles gasoline produces 8x 8.772 = 70.175 moles CO2

= 70.175 X 44 = 3088 g CO2 or 3.088 kg.

The reason burning 1kg of Octane produces so much CO2 is that the unseen reactant is oxygen 8.772 x 12.5 = 109.65 moles of it or 3509g of it. Steam or water vapor is the other product.