By Mara Pesacreta Updated Aug 30, 2022
A decomposition reaction is a type of chemical reaction in which a compound breaks apart into its constituent elements or simpler molecules. Understanding how to write and balance these reactions is essential for accurate calculations and laboratory work.
The standard format for a decomposition reaction is AB → A + B, where AB is the parent compound and A and B are the resulting species. For example, 2HgO → 2Hg + O₂.
Start by writing the chemical formula of the compound you are decomposing. For instance, sodium chloride is represented as NaCl. The elements that make up NaCl are sodium (Na) and chlorine (Cl₂), with chlorine existing as a diatomic molecule.
Using the reactant and product information, draft the preliminary equation: NaCl → Na + Cl₂.
To balance the reaction, the number of atoms for each element must be equal on both sides. In the unbalanced equation above, sodium appears once on each side, but chlorine appears once on the left and twice on the right.
Introduce coefficients to equalize atom counts. Placing a coefficient of 2 in front of NaCl gives two sodium atoms and two chlorine atoms on the reactant side. Adding a coefficient of 2 to the sodium product balances the sodium atoms, yielding the balanced equation: 2NaCl → 2Na + Cl₂.
Follow these steps to confidently write and balance any decomposition reaction.
