To balance a chemical equation, one must keep track of the atoms on each side of the equation as you change the coefficients in front of each component.

Initially CH3Cl + O2 ----> CO2 + H2O + Cl2 has

Reactants Products

C one C one

Cl one Cl two

H three H two

O two O two + one = three

If we balance the Chlorine first by multiplying the CH3CL by 2 we get

2CH3Cl + O2 -----> CO2 + H2O + Cl2

Reactants Product

C two one

Cl two two

H six two

O two two + one = three

We then balance the Carbon by multiplying the CO2 by 2 and the Hydrogen by multiplying H2O by 3

2CH3Cl + O2 ----> 2CO2 + 3 H2O + Cl2

Reactants Products

C two two

Cl two two

H six six

O 2 four + three = 7

We can now balance the oxygen by multiplying the O2 by 7/2

2CH3Cl + 7/2 O2 ----> 2CO2 + 3H2O + Cl2

However, we cannot have a fractional coefficient, so we eliminate the fraction by multiplying each component by a factor of 2

**4CH3Cl + 7O2 ----> 4CO2 + 6H2O + 2Cl2**

Reactants Products

C 4 4

H 12 12

Cl 4 4

O 14 8 + 6 = 14