Rules for Balancing Equations
1) Write the skeleton equation using the correct chemical formulas, with reactants
on the left and products on the right of the arrow.
2) Take “roll”. Count the number of atoms of each type on both sides of the arrow.
For accuracy, write this information down.
3) If polyatomic ions appear on both the reactant and product sides, treat them as a
group
4) Balance the elements one at a time by using coefficients only.
5) In general, leave O2 and H2 until last when balancing.
6) If any substance appears in its elemental form, leave it until last to balance.
7) Check each atom or polyatomic ion to be sure that the equation is balanced and in
reduced form.
8) Learn the diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2
Whenever they appear in a reaction as elements, they should be written as pairs;
e.g. H2, not H .
Remember the 7-UP Rule
Two things you CANNOT do when balancing an equation.
1) You cannot change a subscript.
E.g. Do not change oxygen's subscript in water from one to two, as in:
H2 + O2 → H2O2
2) You cannot place a coefficient in the middle of a formula.
The coefficient goes at the beginning of a formula, not in the middle, as in:
H2 + O2 → H22O
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Balance this equation: H2 + Cl2  HCl
The correctly balanced equation is:
H2 + Cl2  2 HCl
Balance this equation: O2  O3
The correctly balanced equation is:
3 O2  2 O3
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