Write down the number of atoms per each element that you have on each side of the equation.
1) Left side: 3 carbon, 8 hydrogen and 2 oxygen.
Add a coefficient to the single carbon atom on the right of the equation to balance it with the 3 carbon atoms on the left of the equation.
1)
C3H8+O2→H2O+3CO2 2) The coefficient 3 in front of carbon on the right side indicates 3 carbon atoms just as the subscript 3 on the left side indicates 3 carbon atoms.
3) In a chemical equation, you can change coefficients, but you must never alter the subscripts.
Balance the hydrogen atoms next.
You have 8 on the left side. So you'll need 8 on the right side. 1)
C3H8+O2→4H2O+3CO2 2) On the right side, you now added a 4 as the coefficient because the subscript showed that you already had 2 hydrogen atoms.
3) When you multiply the coefficient 4 times by the subscript 2, you end up with 8.
4) The other 6 atoms of Oxygen come from
3CO2.(3×2=6 atoms of oxygen+the other 4=10 Balance the oxygen atoms.
1) Because you've added coefficients to the molecules on the right side of the equation, the number of oxygen atoms has changed. You now have 4 oxygen atoms in the water molecule and 6 oxygen atoms in the carbon dioxide molecule. That makes a total of 10 oxygen atoms.
2) Add a coefficient of 5 to the oxygen molecule on the left side of the equation. You now have 10 oxygen molecules on each side.
3)
C3H8+5O2→4H2O+3CO2 4) The carbon, hydrogen, and oxygen atoms are balanced. Your equation is complete.