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)
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
- 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.
Past Questions from Combination Reaction
- 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
