This is as straightforward as it gets. If however you need to determine how much of each product is produced, then the balanced equation is a must.
Usually, gasoline is expressed as octane in combustion reactions, which means that the balanced equation for its combustion is
2C8H18+25O2→16CO2+18H2O
But, like I've said, for the combined mass of the products all you really need to know is the combined mass of the reactants.
Addendum
Let's say you want to know exactly how much of each compound is formed. In this case, you must check for a limiting reagent. The number of moles of octane is
21⋅103 g⋅1 mole octane114.0 g=184.2 moles
The number of moles of oxygen is
85⋅103 g⋅1 mole O232.0 g=2656 moles
According to the mole ratio between these two, each 2 moles of octane need 25 moles of oxygen, so
noxygen that reacts=noctane⋅252=2303 moles , which means that octane is the limiting reagent. The actual mass of oxygen that reacts is
2303 moles⋅32.0 g1 mole=73.7 kg
This means that the combined mass of the produced water and carbond dioxide is actually
21 kg+73.7 kg=94.7 kg
85 kg−73.7 kg=11.3 kg of oxygen will not react. If you want to count this oxygen as well, the total combined mass of the products will again be 106 kg .
