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Decomposition Reactions
A decomposition reaction occurs when a single compound breaks down into two or more simpler substances. This is the opposite of a combination reaction. Example: AB → A + B
One reactant → Multiple products!
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Thermal Decomposition
When a decomposition reaction is carried out by heating, it's called thermal decomposition. Examples include ferrous sulphate (green to brown), calcium carbonate (limestone to quicklime), and lead nitrate (releasing brown NO₂).
Heat → FeSO₄ breaks into Fe₂O₃ + SO₂ + SO₃
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Electrolytic Decomposition
Decomposition using electricity is called electrolysis. Water splits into hydrogen (collects at cathode, burns with pop sound) and oxygen (collects at anode, relights glowing splint) gases. Volume ratio: 2:1.
Electricity → 2H₂O breaks into 2H₂ + O₂
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Photochemical Decomposition
Decomposition caused by light energy is photochemical decomposition. Silver chloride (white) turns grey in sunlight to form silver metal. Silver bromide behaves similarly. This principle is used in black and white photography!
Sunlight → 2AgCl breaks into 2Ag + Cl₂
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Endothermic Reactions
Decomposition reactions require energy input to break bonds - they absorb energy from surroundings. Reactions in which energy is absorbed are called endothermic reactions. All decomposition reactions shown here are endothermic!
Energy IN = Endothermic! Heat/Light/Electricity absorbed.
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Industrial Applications
Thermal decomposition of limestone (CaCO₃) produces quicklime (CaO) used in cement manufacturing. Electrolysis of water produces hydrogen fuel. Photochemical reactions are used in photography, solar cells, and photosynthesis.
Decomposition reactions power industries and technologies!