1. Balancing Chemical Reactions

2. Step 1
Count the atoms on the left side and on the right side of a reaction.
Mg + O2  MgO
left side right side

3. Step 2
Make the number of atoms on each side of the equation the same by only changing the number in front of the compound (coefficient). Never change the compound itself by changing the little numbers in the compound (subscript numbers).

4. Step 3
Always double check that the number of atoms on the right side of the equation are equal to the left side of the equation.
Example: Balance the following equation:
__Mg + __O2  __MgO
2Mg + 1O2  2MgO

5. Tips on Balancing Equations
1) Try to balance atoms with the greatest atomic number first
Example:
__FeCl3 + __CuS  _1_Fe2S3 + __CuCl2
2FeCl3 + 3CuS + 1Fe2S3 + 3CuCl2

6. Tips on Balancing Equations
Balance the elements that are by themselves last (usually oxygen and hydrogen)
Example:
1C3H8 + __O2  CO H2O
1C3H8 + 5O2  3CO2 + 4H2O

7. Tips on Balancing Equations
Balance polyatomic ions as if they are one element if possible
Example:
__Mg(NO3)2 + __K3PO4  __Mg3(PO4)2 + __KNO3
3Mg(NO3)2 + 2K3PO4  1Mg3(PO4)2 + 6KNO3