Chemical Reactions and Equations
Chemical reactions cause change in identity and nature of substances. Indicators of a chemical reaction: Change in state, Change in color, Evolution of gas, Change in temperature etc.
Types of Chemical Reactions
- Redox Reaction: 3Fe + 4H₂O → Fe₃O₄ + 4H₂
- Combination Reaction – When two or more substances combine to form a single product.
CaO(s)+H2O(l)→Ca(OH)2 (aq) + Heat - Decomposition Reaction – A single compound breaks down into simpler substances.
- (Electrolysis of water produces hydrogen and oxygen gases. Silver chloride turns grey in sunlight, forming silver and chlorine. Silver bromide also decomposes in sunlight similarly.)
(1) CaCO3(s)→ CaO(s)+CO2(g), (2) 2FeSO4 → Fe2O3 + SO2 + SO3 - Displacement Reaction: Iron displaces copper from copper sulphate solution. Iron nail turns brown, and the solution’s blue color fades. Zinc and lead are more reactive and can displace copper from compounds.
- Double Displacement Reaction: Mixing sodium sulphate and barium chloride forms a white precipitate of barium sulphate.
- Oxidation and Reduction (Redox):
- Copper powder turns black on heating due to the formation of copper(II) oxide.
- When hydrogen is passed over hot copper(II) oxide, it reduces to copper.
- Corrosion: The process where metals (like iron) react with substances such as moisture or acids and deteriorate. It is commonly observed as rusting (iron turns reddish-brown). Silver and copper also tarnish.
- Rancidity: Occurs when fats and oils are oxidized, resulting in unpleasant smells and taste. Antioxidants are added to delay rancidity.
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Exothermic in nature (releases heat), Calcium hydroxide is used in whitewashing.
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