Balancing Chemical Reactions
Step 1
• Count the atoms on the left side and on
the right side of a reaction.
Mg + O2  MgO
left side
right side
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).
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
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
Tips on Balancing Equations
• Balance the elements that are by
themselves last (usually oxygen and
hydrogen)
• Example:
1C3H8 + __O2 
CO2 +
H2O
1C3H8 + 5O2  3CO2 + 4H2O
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