NCERT Class X Science Solutions: Chapter 1-Chemical Reactions and Equations Part 2 (For CBSE, ICSE, IAS, NET, NRA 2023)

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Question 7:

Write the balanced chemical equations for the following reactions.

  1. Calcium hydroxide + Carbon dioxide ⇾ Calcium carbonate + Water
  2. Zinc + Silver nitrate ⇾ Zinc nitrate + Silver
  3. Aluminium + Copper chloride ⇾ Aluminium chloride + Copper
  4. Barium chloride + Potassium sulphate ⇾ Barium sulphate + Potassium chloride


Question 8:

Write the balanced chemical equation for the following and identify the type of reaction in each case.


; Double displacement reaction

; Decomposition reaction

; Combination reaction

; Displacement reaction

Question 9:

What does one mean by exothermic and endothermic reactions? Give examples.


Chemical reactions that release energy in the form of heat, light, or sound are called exothermic reactions.

Example: Mixture of sodium and chlorine to yield table salt

In other words, combination reactions are exothermic.

This Diagram Shows Exothermic Reaction

Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.

For example: In the process of photosynthesis, plants use the energy from the sun to convert carbon dioxide and water to glucose and oxygen.

This Diagram Shows Endothermic Reaction

Question 10:

Why respiration is considered an exothermic reaction? Explain.


Energy is required to support life. Energy in our body is obtained from the food we eat. During digestion, large molecules of food are broken down into simpler substances such as glucose. Glucose combines with oxygen in the cells and provides energy. The special name of this combustion reaction is respiration. Since energy is released in the whole process, it is an exothermic process.

Question 11:

Why decomposition reactions are called the opposite of combination reactions? Write equations for these reactions.


Decomposition reactions are those in which a compound breaks down to form two or more substances. These reactions require a source of energy to proceed. Thus, they are the exact opposite of combination reactions in which two or more substances combine to give a new substance with the release of energy.

Decomposition reaction:

Combination reaction: