How do decomposition reactions differ from synthesis reactions?

1 Answer
Jan 16, 2014

They require the addition of energy.


Decomposition Reactions require the addition of energy.

A decomposition reaction is a chemical reaction in which some chemical bonds in a compound are broken and simpler substances are formed. The breaking of chemical bonds requires the addition of energy. We classify decomposition reactions according to the source of the energy.


When a compound is heated, its atoms move about more vigourously. This movement can break chemical bonds. For example, if calcium carbonate is strongly heated, it decomposes into calcium oxide and carbon dioxide.

CaCO₃(s) → CaO(s) + CO₂(g)


In the liquid state, some compounds are decomposed by passing a direct electric current through them. Examples are

2NaCl(l) → 2Na(l) + Cl₂(g)
2H₂O(l) → 2H₂(g) + O₂(g)


Photodecomposition is a chemical reaction in which a substance is broken down into simple substances by exposure to light (photons). For example, silver chloride is converted to silver and chlorine gas on exposure to light.

2AgCl(s) → 2Ag(s) + Cl₂(g)