Types of Chemical Reaction

Table of Contents

TYPES OF CHEMICAL REACTION

Some of the important types of chemical reactions are :
1. Combination reactions,
2. Decomposition reactions,
3. Displacement reactions,
4. Double displacement reactions, and
5. Oxidation and Reduction reactions.

COMBINATION REACTION

  • Those reactions in which two or more substances combine to form a single substance are called combination reactions.

 Example 1: Magnesium and oxygen combine, when heated, to form magnesium oxide.

    •  2Mg (s) + O2 (g)→2MgO (s)

   

 Example 2: Hydrogen burns in oxygen to form water :

              2H2 (g) + O2 (g) → 2H2O (l)

Example 3: Carbon (coal) burns in air to form carbon dioxide :
              C (s) + O2 (g) →  CO2 (g)

CaO reacts with water releases heat

ACTIVITY 1.4

  • Take a small amount of calcium oxide or quick lime in a beaker.
  • Slowly add water to this.
  • What do you feel when touching the beaker?
  • Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
  • CaO(s) + H2O(l) → Ca(OH)2(aq)

IMPORTANT QUESTIONS AND ANSWERS:

Combination reaction

1.Which of the following is a combination :

(a) Cl2 + 2KI → 2KCl + I2
(b) 2K + Cl2 →  2KCl

ANS: (b) is the combination reaction because a combination reaction is in which two or more substances combine to form a single substance.

EXOTHERMIC REACTION AND ENDOTHERMIC REACTION

difference between exothermic reaction and endothermic reaction
difference between exothermic reaction and endothermic reaction
  • Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.

Examples of Exothermic Reaction

  • Burning of natural gas
  • Respiration reaction in human beings
  • The decomposition of vegetable matter into compost

Reactions in which heat is absorbed along with the formation of products are called endothermic chemical reactions.

Examples of Endothermic Reaction

  • Melting ice cubes.
  • Melting solid salts.
  • Evaporating liquid water.
exothermic reaction and endothermic reaction
exothermic reaction and endothermic reaction

Past Questions from

  • Quick lime reacts vigorously with water to produce calcium hydroxide (slaked lime) releasing a large amount of heat (exothermic reaction)

CaO(s) + H2O(l) →Ca(OH)2(aq) + heat

 

  • The substance which we use for white-washing our house is lime (or quicklime) which is calcium oxide (CaO).
  • We put calcium oxide in a drum and add water to it slowly.
  • Calcium oxide reacts with water vigorously to form a white solid called calcium hydroxide (or slaked lime) with the evolution of heat.
  • More water is then added to get calcium hydroxide solution.
  • This calcium hydroxide solution is then applied to the walls of the house with a brush.
  • The calcium hydroxide solution, when applied to the walls, reacts slowly with the carbon dioxide gas
    present in air to form a thin, shining layer of calcium carbonate on the walls of the house :
  • Ca(OH)2 (aq) + CO2 (g) →CaCO3 (s) + H2O (l)
  • Since this process gives a white, shiny appearance to the walls of a house, it is called white-washing.
  • The calcium carbonate is actually formed after two to three days of white-washing and gives a shiny finish to the walls
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