Balancing Chemical Equations

Rules

All of the following rule must be obeyed when balancing chemical equations.

  1. The formulas for molecules and ion cannot be changed.
  2. The total number of atoms cannot change. For each type of atom, the number of that type of atom in the reactants must equal the number of that type of atom in the products.
  3. The total charges must balance (total charge of all reactants must equal total charge of all products).
  4. To be correct, the balanced chemical equation must contain the simplest ratio of integer (whole number) coefficients.

Hints

When balancing chemical equations, it is almost always best to start with the 'simplest' atom(s). The 'simplest' atom means an atom that appears in only one molecule/ion on the reactant side and in only one molecule/ion on the product side.

Graphical Examples

Combustion of Methane Combustion of Propane

Procedure for Balancing Equations

  C2H5OH + O2 → CO2 + H2O
C: 2   -   1   -
C: 1 C2H5OH + ___ O2 → 2 CO2 + ___ H2O
H: 6   -   -   2
H: 1 C2H5OH + ___ O2 → 2 CO2 + 3 H2O
O: 1   2   4   3
O: (Don't change)     (7 total)
O: 1 C2H5OH + 3 O2 → 2 CO2 + 3 H2O