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A chemical reaction in which molecules of a substance break down to form simpler molecules of two or more new substances is recognized as a decomposition reaction. When a substance, decomposes due to heat it is called thermal decomposition, while decomposition due to electricity, is called electrolytic decomposition.
- Mercuric oxide, when heated, undergoes thermal decomposition, to give mercury and oxygen.
- Similarly, if blue crystals of copper nitrate are heated, they undergo thermal decomposition to give black coloured copper oxide, reddish brown fumes of nitrogen dioxide, and a colourless gas of oxygen.
- When water taken in an electrolytic cell, is acidified with a small quantity of sulphuric acid and a direct current passed through; it undergoes electrolytic decomposition to yield hydrogen and oxygen.
- If an electric current is passed through molten lead bromide, it decomposes to give lead and bromine.
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