14 oxygen molecules
First, count the number of carbon and hydrogen are in the original molecule of c9h20
9 carbon.
20 hydrogen.
Each carbon atom will make 1 molecule of CO2 and will require 2 oxygen atoms per molecule, so multiply 9 by 2 to get the number of oxygen atoms needed.
9 * 2 = 18
It takes 2 hydrogen atoms to make a water molecule and it takes 1 oxygen atom. So divide the number of hydrogen atoms by 2 to get the number of water molecules you can make.
20 / 2 = 10
So you need a total of 18 plus 10 oxygen atoms giving a total of 18+10 = 28 oxygen atoms.
But you don't want to know the number of oxygen atoms, you want to know the number of oxygen molecules. Since there's 2 oxygen atoms per oxygen molecule, just divide by 2. Giving 28 / 2 = 14
Therefore you need 14 oxygen molecules for full combustion of 1 C9H20 molecule.
