In this type of adjustment we search for the stoichiometric coefficients that adjust the chemical equation. To simplify this operation we follow some simple guidelines.

  • Elements that appear in only one reactant and product are matched first.
  • Free elements fit last.
  • The use of fractional coefficients can facilitate the adjustment. These fractional coefficients can be eliminated by multiplying the entire equation by the common denominator.

As an example, let's adjust the reaction \(NH_3 + O_2 \rightarrow NO_2 + H_2O\).

First we fit the hydrogen atoms with a coefficient 3/2 in front of the water. The number of oxygens in the products becomes 2 + 3/2 = 7/2. Multiplying the oxygen of the reagents by 7/4 we complete the adjustment.

$$NH_3 + \frac{7}{4}O_2 \rightarrow NO_2 + \frac{3}{2}H_2O$$

Multiplying the equation by 4 gives integer stoichiometric coefficients

$$4NH_3+7O_2\rightarrow 4NO_2 + 6H_2O$$