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Types of Chemical Reactions - Decomposition Reactions

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  • Decomposition Reactions
  • Experiment: Correct way of heating the boiling tube containing crystals of ferrous sulphate and of smelling the odour.
  • Experiment: Heating of lead nitrate and emission of nitrogen dioxide (Thermal decomposition reaction).
  • Experiment: Electrolysis of water.
  • Experiment: Silver chloride turns grey in sunlight to form silver metal.



Decomposition reaction is the breakdown of a single entity (normal molecule, reaction intermediate, etc.) into two or more fragments. Chemical decomposition is usually regarded and defined as the exact opposite of chemical synthesis. In short, the chemical reaction in which two or more products are formed from a single reactant is called a decomposition reaction.

2FeSO4(s)+Heat → Fe2O3(s) + SO2(g) + SO3(g)

In this reaction you can observe that a single reactant breaks down to give simpler products. This is a decomposition reaction. Ferrous sulphate crystals (FeSO4, 7H2O) lose water when heated and the colour of the crystals changes. It then decomposes to ferric oxide (Fe2O3), sulphur dioxide (SO2) and sulphur trioxide (SO3). Ferric oxide is a solid, while SO2 and SO3 are gases.


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