CBSE Class 10 Science Chapter 1: Chemical Reactions and Equations NCERT Solutions

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NCERT Solutions PDF Class 10 PDF

This comprehensive set of NCERT Solutions for CBSE Class 10 Science, Chapter 1, focuses on Chemical Reactions and Equations. It covers key concepts such as distinguishing between physical and chemical changes, identifying different types of chemical reactions including displacement, combination, redox, and neutralization reactions. The solutions also delve into the oxidation and reduction processes within a reaction, the role of oxidizing and reducing agents, and the identification of exothermic and endothermic processes. Through detailed explanations and step-by-step problem-solving, these solutions aim to build a strong foundation for students, aiding them in understanding the fundamental principles of chemistry and preparing effectively for their examinations.

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BoardCBSE
ClassClass 10
SubjectScience (Exemplar)
Session2026
LanguageEnglish
TypeNCERT Solutions
Chapter1. Chemical Reactions and Equations

Chapter summary

This chapter's NCERT Solutions for Class 10 Science provide a thorough exploration of chemical reactions and equations. It clarifies the distinction between physical and chemical changes, with a focus on irreversible processes like combustion. The solutions detail various reaction types, including displacement, combination, redox, and neutralization, and explain oxidation/reduction using specific examples. It also covers identifying exothermic and endothermic processes, crucial for understanding energy changes in reactions. These solutions are designed to help students grasp the core concepts and practice problem-solving effectively.

Learning outcomes

  • Differentiate between physical and chemical changes.
  • Identify and classify different types of chemical reactions.
  • Understand the concepts of oxidation and reduction.
  • Recognize oxidizing and reducing agents in a reaction.
  • Identify exothermic and endothermic processes.

Topics covered

Paper topics

  • Physical Changes
  • Chemical Changes
  • Chemical Reactions
  • Types of Chemical Reactions
  • Combination Reactions
  • Decomposition Reactions
  • Displacement Reactions
  • Double Displacement Reactions
  • Oxidation and Reduction
  • Redox Reactions
  • Exothermic Processes
  • Endothermic Processes

Important topics

  • Distinguishing Physical and Chemical Changes
  • Identifying Types of Chemical Reactions
  • Understanding Oxidation and Reduction
  • Recognizing Oxidizing and Reducing Agents
  • Identifying Exothermic and Endothermic Processes

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Questions and Solutions

Multiple Choice Questions

1. Which of the following is not a physical change?

(i) Boiling of water to give water vapour

(ii) Melting of ice to give water

(iii) Dissolution of salt in water

(iv) Combustion of Liquefied Petroleum Gas (LPG)

Solution: The correct option is (iv) Combustion of Liquefied Petroleum Gas (LPG).

A physical change is a change in the form of a substance that does not alter its chemical identity and is often reversible. Examples include melting, boiling, and dissolving. A chemical change, however, results in the formation of new chemical substances with different properties and is usually irreversible. Combustion involves burning, which produces new substances like carbon dioxide and water, and releases energy. Therefore, it is a chemical change, not a physical one.

Multiple Choice Questions

2. The following reaction is an example of which type(s) of reactions?

4NH_3(g) + 5O_2(g) \rightarrow 4NO(g) + 6H_2O(g)

Options:

(i) displacement reaction

(ii) combination reaction

(iii) redox reaction

(iv) neutralisation reaction

Correct choice is:

(a) (i) and (iv)

(b) (ii) and (iii)

(c) (i) and (iii)

(d) (iii) and (iv)

Solution: The correct option is (c) (i) and (iii).

This reaction is a displacement reaction because oxygen displaces hydrogen from ammonia. It is also a redox reaction. Let's analyze the oxidation states: In NH3, H is +1, so N is -3. In O2, O is 0. In NO, O is -2, so N is +2. In H2O, H is +1, O is -2. Nitrogen's oxidation state changes from -3 in NH3 to +2 in NO, indicating oxidation. Oxygen's oxidation state changes from 0 in O2 to -2 in NO and H2O, indicating reduction. Since oxidation and reduction occur simultaneously, it is a redox reaction. It is not a combination reaction as multiple reactants form multiple products, nor a neutralisation reaction as no acid-base reaction is involved.

Multiple Choice Questions

3. Which of the following statements about the given reaction are correct?

3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g)

(i) Iron metal is getting oxidised

(ii) Water is getting reduced

(iii) Water is acting as reducing agent

(iv) Water is acting as oxidising agent

Options:

(a) (i), (ii) and (iii)

(b) (iii) and (iv)

(c) (i), (ii) and (iv)

(d) (ii) and (iv)

Solution: The correct option is (c) (i), (ii) and (iv).

Let's analyze the oxidation states: In Fe(s), the oxidation state of Fe is 0. In Fe3O4(s), let the oxidation state of Fe be x. Then 3x + 4(-2) = 0, so 3x = +8, and x = +8/3. Since the oxidation state of iron increases from 0 to +8/3, iron metal is getting oxidised (Statement i is correct). In H2O(g), the oxidation state of O is -2 and H is +1. In H2(g), the oxidation state of H is 0. Oxygen's oxidation state remains -2, but hydrogen's oxidation state changes from +1 in H2O to 0 in H2. This means hydrogen is gaining electrons and is being reduced. Since oxygen is part of water and is involved in the reduction of hydrogen, water is getting reduced (Statement ii is correct). An oxidizing agent is a substance that causes oxidation in another substance and is itself reduced. Here, water causes iron to be oxidized and is itself reduced (by losing hydrogen which gets reduced). Therefore, water is acting as an oxidizing agent (Statement iv is correct). Statement (iii) is incorrect because water is acting as an oxidizing agent, not a reducing agent.

Multiple Choice Questions

4. Which of the following are exothermic processes?

(i) Reaction of water with quick lime

(ii) Dilution of an acid

(iii) Evaporation of water

(iv) Sublimation of camphor (crystals)

Options:

(a) (i) and (ii)

(b) (ii) and (iii)

(c) (i) and (iv)

(d) (iii) and (iv)

Solution: The correct option is (a) (i) and (ii).

Exothermic processes are those that release energy, usually in the form of heat, into the surroundings. The reaction of water with quick lime (calcium oxide, CaO) to form calcium hydroxide (Ca(OH)2) is a highly exothermic reaction, producing significant heat. Similarly, the dilution of concentrated acids with water is also an exothermic process, where heat is released. Evaporation of water (changing from liquid to gas) and sublimation of camphor (changing directly from solid to gas) require energy input from the surroundings to occur, making them endothermic processes.

Common mistakes

  • Confusing physical changes with irreversible chemical changes.
  • Incorrectly identifying oxidizing and reducing agents.
  • Misclassifying reaction types (e.g., redox vs. displacement).
  • Difficulty in recognizing exothermic and endothermic processes.

Revision tips

  • Focus on the definitions and examples of physical vs. chemical changes.
  • Practice identifying the type of reaction for given chemical equations.
  • Pay close attention to the oxidation states to identify redox reactions.
  • Memorize common examples of exothermic and endothermic processes.

Practice MCQs

Q1. Which of the following processes is NOT considered a physical change?

Q2. The reaction 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) is an example of which type(s) of reactions?

Q3. In the reaction 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g), what role does water play?

Q4. Which of the following processes are exothermic?

Frequently asked questions

What is the main difference between a physical and a chemical change?

A physical change alters the form or appearance of a substance but not its chemical composition (e.g., melting ice). A chemical change results in the formation of new substances with different properties (e.g., burning wood).

How can I identify a redox reaction?

A redox reaction involves a change in the oxidation states of atoms. One substance is oxidized (loses electrons/increases oxidation state), and another is reduced (gains electrons/decreases oxidation state).

What are exothermic and endothermic processes?

Exothermic processes release heat into the surroundings (e.g., combustion), while endothermic processes absorb heat from the surroundings (e.g., photosynthesis).

How do these NCERT Solutions help with Class 10 Science revision?

These solutions provide clear, step-by-step explanations for each question, helping students understand complex concepts like reaction types and redox processes, which are crucial for exam preparation.

What is the role of an oxidizing agent in a chemical reaction?

An oxidizing agent is a substance that causes another substance to be oxidized (lose electrons) and is itself reduced (gains electrons) in the process.

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