Types of Chemical Reaction

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1. Decomposition reactions

In these reactions, compound either of its own or upon heating decomposes to give two or more components out of which at least one is in the elemental state.
      2NaH (s) → Na (s) + H2 (g)
      2H2O(l) → 2H2(g) + O2(g)

2. Combination reactions

In combination reactions, compounds are formed as a result of the chemical combination of two or more elements.
      H2(g) + ½.O2(g) → H2O2(l)
      C (s) + O2 (g) → CO (g)
      3Mg (s) + N2 (g) → Mg3N2 (s)

3. Displacement reactions

In these reactions, an atom or ion present in a compound gets replaced by an atom/ion of another element.
      FeSO4 (aq) + Zn (s) → Zn SO4 (aq) + Fe (s)
      MgO (aq) + 2 Na (s) → Na2O (aq) + Mg (s)

4. Disproportionation reactions

The chemical reaction in which only one substance is oxidised as well as reduced simultaneously is called disproportionation reaction.
      Cl2 + 2NaOH → NaCl + NaOCl + H2O
      P4 + NaOH + 2 H2O → 2NaH2PO2 + 2PH3

5. Substitution reaction

In these reactions, one or more atoms or groups present in organic molecule get substituted or replaced by suitable atoms or groups.
      C2H2C1 + KOH (aq) → C2H5OH + KC1
Ethyl chloride                  Ethyl alcohol

6. Neutralisation reaction

When an acid reacts with a base, salt and water is formed. This reaction is called neutralisation reaction.
      acid + base ―→ salt + water
    HC1 + NaOH → NaCl + H2O

7. Reversible reaction

A reaction in which reactants combine to form products and again products recombine to reactants is called reversible reaction.
      N2 (g) + 3H2(g) ↔ 2NH3(g)

8. Irreversible reaction

A reaction which proceeds in only one direction is called irreversible reaction.
      CaCO3 (s) ―→ CaO (s) + CO2 (g)

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