Question

How would you write a balanced equation for the combustion of octane, C8H18 with oxygen to obtain carbon dioxide and water?

Answer 1

`2C_8H_18 + 25O_2 -> 16CO_2 + 18H_2O`

Explanation:

You just have to check the number of atoms of each element is the same in both sides.
You can do it by steps starting with the unbalanced equation

`C_8H_18 + O_2 -> CO_2 + H_2O`

By making a list of the elements and the number of atoms on each side of the equation

`8-C-1`
`18-H-2`
`2-O-3`

Then as you can see, the molecule with 1 carbon (`CO_2`) you have to multiply by eight, the molecule with 2 hydrogens (`H_2O`) you have to multiply it by 9 to be equal to the left. And when you find that you have to multiply by a fraction then you can multiply the whole equation by an integer so you have only integers.