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Showing posts with label Types of Chemical Reaction. Show all posts
Showing posts with label Types of Chemical Reaction. Show all posts

Sunday, 11 January 2026

TYPES OF CHEMICAL REACTIONS at a glance

  Chemical reactions are reactions in which elements or/and compounds combine chemically to form new substances.

There are different types of chemical reactions, they include 

1.   Combinations reactions 

2.   Decomposition reactions 

3.   Displacement reaction

4.   Double decomposition reaction

5.   Thermal Dissociation reaction 

6.    Reversible reaction

7.  Catalytic reaction


🔗 Combination Reaction (Short Note)

A combination reaction is a chemical reaction in which two or more substances combine to form one single product.

It is also called a synthesis reaction.

General Form

A + B → AB

Examples

  1. Formation of magnesium oxide

    2Mg(s) + O2(g) →2MgO(s)

  2. Formation of water

    2H2(g) + O2(g) →2H2O(l)

  3. Formation of ammonia  

    N2(g) + 3H2(g) →2NH3(g)

  4. Formation of calcium oxide

    CaO(s) + CO2(g)→ CaCO3(s)

🧠 Important Tip

In a combination reaction, many reactants give one product.

🧪 Decomposition Reaction

A decomposition reaction is a chemical reaction in which one compound breaks down into two or more simpler substances when heat, electricity, or light is applied.

General Form


AB → A + B

Types and Examples

1. Thermal Decomposition (by heat)


CaCO3(s) {heat} CaO(s) + CO2(g)

(Calcium carbonate breaks into calcium oxide and carbon dioxide.)

2. Electrolytic Decomposition (by electricity)


2H2O(l) {electricity} 2H2(g) + O2(g)

3. Photochemical Decomposition (by light)


2AgCl(s) {sunlight} 2Ag(s) + Cl2(g)

🧠 Important Tip

If one compound splits into two or more products, it is a decomposition reaction.


🔁 Displacement Reactions 

A displacement reaction is a chemical reaction in which a more reactive element replaces a less reactive element from its compound.

It usually occurs between a metal and a salt solution.

General Equation

A + BC → AC + B
(Where A is more reactive than B)

Examples

  1. Zinc and copper (II) sulphate
    Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

  2. Zinc displaces copper because zinc is more reactive.

  3. Iron and copper (II) sulphate

    Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

  4. Copper and silver nitrate

  5. Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)

Important Points

  • Only a more reactive metal can displace a less reactive metal.

  • The reaction depends on the reactivity series.

🧠 Important Tip

If a metal is higher in the reactivity series, it will displace a metal below it from solution.


🔄 Double Decomposition Reaction

A double decomposition reaction (also called double displacement or metathesis reaction) is a chemical reaction in which two compounds exchange their ions to form two new compounds.

General Form


AB + CD → AD + CB

Examples

  1. Reaction between sodium chloride and silver nitrate

    NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq)

  2. Reaction between barium chloride and sodium sulphate

    BaCl2(aq) + Na2SO4(aq) →BaSO4(s) + 2NaCl(aq)

  3. Reaction between hydrochloric acid and sodium hydroxide

    HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

(This is also a neutralization reaction.)

Important Points

  • The reaction usually occurs in aqueous solution.

  • One of the products is often a precipitate, gas, or water.

🧠 Important Tip

If two compounds exchange ions to form new compounds, it is a double decomposition reaction.

🔥 Thermal Dissociation (Short Note)

Thermal dissociation is a process in which a compound splits into simpler substances when heated, and the reaction is reversible.

When the temperature is lowered, the products can recombine to form the original compound.

General Form


AB →  A + B


Examples

  1. Ammonium chloride

    NH4Cl(s) \xrightleftharpoons{heat} NH3(g) + HCl(g)

  2. Dinitrogen tetroxide
    [
    N2O4(g) \xrightleftharpoons{heat} 2NO2(g)
    ]

  3. Calcium carbonate
    [
    CaCO3(s) \xrightleftharpoons{heat} CaO(s) + CO2(g)
    ]

🧠 Important Tip

If a substance breaks on heating and reforms on cooling, it shows thermal dissociation.


🔄 Reversible Reaction

A reversible reaction is a chemical reaction in which the products can react together to reform the original reactants.

It occurs in both forward and backward directions at the same time.

Symbol

[
A + B \rightleftharpoons C + D
]

Examples

  1. Formation of ammonium chloride

    NH3(g) + HCl(g) → NH4Cl(s)

  2. Dinitrogen tetroxide and nitrogen dioxide

  3. N2O4(g) ⇌ 2NO2(g) 

  4. Haber process

    N2(g) + 3H2(g)⇌ 2NH3(g)
     

🧠 Important Tip

If a reaction can go both forward and backward, it is a reversible reaction.


⚡ Catalytic Reaction

A catalytic reaction is a chemical reaction in which a substance called a catalyst increases the rate of the reaction without being used up or changed permanently.

Catalyst

A catalyst is a substance that speeds up a chemical reaction but remains unchanged at the end of the reaction.

Examples

  1. Decomposition of hydrogen peroxide

  2.   2H2O2(aq) ---{MnO2}--->2H2O(l) + O2(g)

  3. Haber process (manufacture of ammonia)

    N2(g) + 3H2(g) ---{Fe}---> 2NH3(g)

  4. Contact process (manufacture of tetraoxosulphate VI acid)

    2SO2(g) + O2(g) ---{V2O5}---> 2SO3(g)

🧠 Important Tip

A catalyst alters the rate of a reaction but is not used up in the process.


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