Balance the following equation: __C8H18 + __ O2 --> __CO2 + __H2O

Balancing the equation means there must be an equal number of each element on both sides of the equation. In this case, we start with 8 carbon atoms on the left and just 1 on the right, so we can put 8 molecules of CO2 on the right hand side. Similarly, there are 18 hydrogen atoms on the left but only 2 on the right, so to scale it up to 18 you would need 9 H2O molecules. Finally to balance the oxygen molecules, we have 2 atoms on the left hand side but we now have 25 on the right hand side (8 x CO2 + 9 x H2O = 25 oxygen atoms), so to balance this we need 12.5 oxygen atoms on the left hand side. This gives 1 C8H18 + 12.5 O2 --> 8 CO2 + 9 H2O To get rid of the decimal in the equation, you could multiply all the numbers by 2 to give 2 C8H18 + 25 O2 --> 16 CO2 + 18 H2O