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Types of Chemical Reactions > Decomposition Reaction

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Topics

  • Definition: Decomposition Reaction
  • Definition: Thermal Decomposition
  • Key Points: Decomposition Reaction
CBSE: Class 10
Maharashtra State Board: Class 10

Definition: Decomposition Reaction

A single reactant breaks down to give simpler products. This is a decomposition reaction.

OR

The chemical reaction in which two or more products are formed from a single reactant is a decomposition reaction.

CBSE: Class 10

Definition: Thermal Decomposition

When a decomposition reaction is carried out by heating, it is called thermal decomposition.

CBSE: Class 10
Maharashtra State Board: Class 10

Key Points: Decomposition Reaction

  • Thermal decomposition involves heating a compound to break it into simpler substances, e.g.,
    2Pb(NO₃)₂ ⟶ 2PbO + 4NO₂ + O₂ (brown fumes of NO₂ observed).
  • Electrolytic decomposition uses electricity to decompose compounds, e.g.,
    2H₂O ⟶ 2H₂ + O₂ (Electrolysis of water gives hydrogen and oxygen gases).
  • Photodecomposition occurs when light energy breaks down a compound, e.g.,
    2AgCl ⟶ 2Ag + Cl₂ (white silver chloride turns grey in sunlight).
  • Thermal decomposition of calcium carbonate produces lime (CaO) and CO₂ gas, which turns lime water milky.
  • Decomposition reactions are usually endothermic and require heat, light, or electricity to occur (e.g., the decomposition of ferrous sulphate, calcium carbonate, or sugar).
 
Maharashtra State Board: Class 10

Experiment

1. Aim: To observe and understand decomposition reactions, where a single reactant breaks down into two or more simpler substances.

2. Requirements

  • Apparatus: evaporating dish, test tubes, bent tube, rubber cork, Bunsen burner.
  • Chemicals: sugar, calcium carbonate (CaCO₃), sulphuric acid, freshly prepared lime water.

4. Procedure

Experiment 1: Decomposition of Sugar

  • Take some sugar in an evaporating dish.
  • Heat it using a Bunsen burner and observe the changes.
  • A black residue (carbon) forms, and water (H₂O) vapour is released.

\[\mathrm{C}_{12}\mathrm{H}_{22}\mathrm{O}_{11}\xrightarrow{\mathrm{Heat}}12C+11H_2O\]

Experiment 2: Decomposition of Calcium Carbonate

  • Take some calcium carbonate (CaCO₃) in a test tube.
  • Fit a bent tube into the test tube using a rubber cork.
  • Insert the other end of the bent tube into another test tube containing freshly prepared lime water.
  • Heat the calcium carbonate strongly. The lime water turns milky, indicating the presence of carbon dioxide (CO₂) gas.

\[\mathrm{CaCO}_3(s)\xrightarrow{\Delta}\mathrm{CaO}(s)+\mathrm{CO}_2\uparrow\]

Decomposition of calcium carbonate

Experiment 3: Electrolysis of Water

  1. Pass electric current through acidulated water.
  2. Observe the formation of hydrogen (H₂) and oxygen (O₂) gases.

\[2H_2O(l)\xrightarrow{\text{Electrical Energy}}2H_2\uparrow+O_2\uparrow\]

5. Conclusion: A decomposition reaction occurs when a single reactant breaks down into two or more simpler substances. These reactions can be thermal (heat-driven), electrolytic (electricity-driven), or biological (natural degradation by microorganisms). Decomposition reactions are crucial in nature, industry, and energy production, such as in the formation of biogas from organic waste.

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Related QuestionsVIEW ALL [80]

Complete the following reaction:

\[\ce{C_12H_22O11->[Heat]}\] ______ + ______.

Give one example of a decomposition reaction which is carried out by applying heat.

The white solid compound A decomposes quite rapidly on heating in the presence of a black substance X to form a solid compound B and a gas C. When an aqueous solution of compound B is reacted with silver nitrate solution, then a white precipitate of silver chloride is obtained along with potassium nitrate solution. Gas C does not burn itself but helps burn other things.
(a) What is compound A?
(b) What is compound B?
(c) What is gas C?
(d) What do you think is the black substance X? What is its function?
(e) What is the general name of substances like X?

Give a balanced equation for –

A white precipitate obtained during a double decomposition reaction involving a silver salt with sodium salt.

Taking into consideration the relationship in the first pair, complete the second pair

2H2 + O2 → 2H2O :Combination Reaction :: 2HgO → 2Hg + O2:_________

What type of reaction is represented by the digestion of food in our body?

MULTIPLE CHOICE QUESTIONS

Tick the most appropriate answer.

Thermal decomposition of a substance is brought about with the help of

  1. reactants
  2. water
  3. wind
  4. heat

What type of chemical reaction take place when silver bromide is exposed to sunlight?

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