In this example, none of the rules apply except the last rule. We have to just go back and forth by trial and error until the equation is balanced. We notice that there are four hydrogen atoms on the left side of the equation and only two hydrogen atoms on the right side of the equation. If we multiply the H2O by 2, we can balance out the hydrogen atoms.
CH4
+ O2
®
CO2 +
2 H2O
This gives a total of four oxygen atoms on the right side of the equation and only two oxygen atoms on the left side of the equation. If we multiply the O2 by 2, we can balance out the oxygen atoms. We now have a balanced equation.
CH4 + 2
O2
®
CO2 +
2 H2O