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What are the main types of chemical reactions?

Class 10 ScienceNCERT chapter: Chemical Reactions and Equationsइसे हिंदी में पढ़ें

Exam-ready answer

The main types of chemical reactions are combination, decomposition, displacement, double displacement, and oxidation-reduction (redox) reactions. In combination, two or more reactants form a single product; decomposition breaks a compound into simpler substances; displacement involves a more reactive element replacing a less reactive one; double displacement involves exchange of ions; redox involves simultaneous oxidation and reduction.

Explanation

Chemical reactions are classified based on how atoms rearrange. In a combination reaction, two or more substances combine to form a single product. For example, calcium oxide reacts with water to form calcium hydroxide: CaO(s) + H2O(l) → Ca(OH)2(aq). This is also called a synthesis reaction.

In a decomposition reaction, a single compound breaks down into two or more simpler substances. It usually requires energy in the form of heat, light, or electricity. For example, calcium carbonate decomposes on heating to give calcium oxide and carbon dioxide: CaCO3(s) → CaO(s) + CO2(g).

In a displacement reaction, a more reactive element displaces a less reactive element from its compound. For example, iron displaces copper from copper sulphate solution: Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s). In a double displacement reaction, ions exchange partners, often forming a precipitate, e.g., sodium sulphate reacts with barium chloride to form barium sulphate precipitate: Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq). Redox reactions involve both oxidation and reduction, such as in the reaction of copper oxide with hydrogen.

Points to remember

  1. Combination reaction: A + B → AB (e.g., CaO + H2O → Ca(OH)2).
  2. Decomposition reaction: AB → A + B (e.g., CaCO3 → CaO + CO2).
  3. Displacement reaction: A + BC → AC + B (e.g., Fe + CuSO4 → FeSO4 + Cu).
  4. Double displacement reaction: AB + CD → AD + CB (e.g., Na2SO4 + BaCl2 → BaSO4 + 2NaCl).
  5. Redox reaction: oxidation and reduction occur simultaneously (e.g., CuO + H2 → Cu + H2O).

Exam tip

Always write balanced chemical equations with state symbols (s, l, g, aq) for each type of reaction. For double displacement, mention the precipitate formed.

Questions students also ask

What is a combination reaction? Give an example.
A combination reaction is a reaction in which two or more reactants combine to form a single product. Example: CaO(s) + H2O(l) → Ca(OH)2(aq).
What is the difference between displacement and double displacement reactions?
In a displacement reaction, a more reactive element displaces a less reactive element from its compound. In a double displacement reaction, two compounds exchange ions to form two new compounds, often producing a precipitate.
What is a redox reaction?
A redox reaction is a reaction in which one substance gets oxidised (gains oxygen or loses hydrogen) and another gets reduced (loses oxygen or gains hydrogen) simultaneously. Example: CuO + H2 → Cu + H2O.

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