Question

A balanced equation for the combustion of octane with oxygen to obtain carbon dioxide and water

Answer 1

Octane is C8H18, Carbon Dioxide is CO2, Oxygen is O2, and water is H2O.  Thus, the reaction will be in the form:

C8H18+O2 -> CO2+H2O

However, it is not balanced.  We start with just one C8H18.  This requires 8 CO2s to account for the 8 carbon atoms and 9 H2Os to account for the 18 hydrogen atoms.  This is a total of 8*2+9=25 oxygen atoms.  We can't have 25/2 of a molecule, so we multiply all coefficients by two.  Therefore, our balanced equation is:

2 C8H18 + 25 O2 -> 16 CO2 + 18 H2O