Short Intro

Chemical Reactions and Equations is the first chapter of Class 10 Science. This chapter explains chemical reactions, balancing chemical equations, types of reactions, oxidation, reduction, corrosion, and rancidity. These NCERT solutions provide step-by-step explanations for all important questions and help students prepare effectively for board examinations.

Quick Information Box

Particular	Details
Chapter Name	Chemical Reactions and Equations
Class	10
Subject	Science
Board	CBSE/State Boards
Important Topics	Balancing Equations, Oxidation, Reduction, Types of Reactions
Exam Weightage	High

Concepts Used (Topics Covered)

• Chemical Reactions
• Chemical Equations
• Balanced Chemical Equations
• Combination Reactions
• Decomposition Reactions
• Displacement Reactions
• Double Displacement Reactions
• Oxidation and Reduction
• Corrosion
• Rancidity

Important Formulas

1. Law of Conservation of Mass
   Total mass of reactants = Total mass of products
2. Combination Reaction
   A + B → AB
3. Decomposition Reaction
   AB → A + B
4. Displacement Reaction
   A + BC → AC + B
5. Double Displacement Reaction
   AB + CD → AD + CB

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Question 1

Which statements are incorrect?

2PbO + C → 2Pb + CO₂

Solution

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Question 2

Fe₂O₃ + 2Al → Al₂O₃ + 2Fe

Solution

Aluminium displaces iron from iron oxide.

Answer

(d) Displacement Reaction

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Question 3

What happens when dilute hydrochloric acid is added to iron filings?

Solution

Iron reacts with HCl to form iron chloride and hydrogen gas.

Fe + 2HCl → FeCl₂ + H₂

Answer

(a) Hydrogen gas and iron chloride are produced.

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Question 4

What is a balanced chemical equation? Why should chemical equations be balanced?

Solution

A balanced chemical equation has an equal number of atoms of each element on both sides.

Chemical equations are balanced because of the Law of Conservation of Mass.

Answer

A balanced chemical equation contains equal numbers of atoms of every element on both sides. It is balanced to satisfy the law of conservation of mass.

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Question 5

Translate and balance the equations.

(a)

Hydrogen + Nitrogen → Ammonia

N₂ + 3H₂ → 2NH₃

(b)

Hydrogen sulphide + Oxygen → Water + Sulphur dioxide

2H₂S + 3O₂ → 2H₂O + 2SO₂

(c)

Barium chloride + Aluminium sulphate → Aluminium chloride + Barium sulphate

3BaCl₂ + Al₂(SO₄)₃ → 2AlCl₃ + 3BaSO₄

(d)

Potassium + Water → Potassium hydroxide + Hydrogen

2K + 2H₂O → 2KOH + H₂

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Question 6

Balance the following equations.

(a)

2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O

(b)

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

(c)

NaCl + AgNO₃ → AgCl + NaNO₃

(d)

BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl

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Question 7

(a)

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

(b)

Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag

(c)

2Al + 3CuCl₂ → 2AlCl₃ + 3Cu

(d)

BaCl₂ + K₂SO₄ → BaSO₄ + 2KCl

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Question 8

(a)

2KBr + BaI₂ → 2KI + BaBr₂

Type: Double Displacement

(b)

ZnCO₃ → ZnO + CO₂

Type: Decomposition

(c)

H₂ + Cl₂ → 2HCl

Type: Combination

(d)

Mg + 2HCl → MgCl₂ + H₂

Type: Displacement

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Question 9

What are exothermic and endothermic reactions?

Solution

Exothermic reactions release heat.

Example:
CH₄ + 2O₂ → CO₂ + 2H₂O + Heat

Endothermic reactions absorb heat.

Example:
CaCO₃ → CaO + CO₂

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Question 10

Why is respiration exothermic?

Solution

During respiration, glucose reacts with oxygen and releases energy.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

Hence respiration is exothermic.

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Question 11

Why are decomposition reactions opposite to combination reactions?

Solution

Combination:
A + B → AB

Decomposition:
AB → A + B

Combination forms one product while decomposition breaks one compound into simpler substances.

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Question 12

Examples of decomposition reactions

Heat:
CaCO₃ → CaO + CO₂

Light:
2AgCl → 2Ag + Cl₂

Electricity:
2H₂O → 2H₂ + O₂

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Question 13

Difference between displacement and double displacement reactions

Displacement:
One element replaces another.

Zn + CuSO₄ → ZnSO₄ + Cu

Double displacement:
Exchange of ions occurs.

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

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Question 14

Silver recovery reaction

Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag

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Question 15

Precipitation Reaction

A reaction producing an insoluble solid is called a precipitation reaction.

Example:

Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl

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Question 16

(a) Oxidation

Addition of oxygen or removal of hydrogen.

Examples:
2Cu + O₂ → 2CuO
C + O₂ → CO₂

(b) Reduction

Removal of oxygen or addition of hydrogen.

Examples:
CuO + H₂ → Cu + H₂O
ZnO + C → Zn + CO

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Question 17

A shiny brown element becomes black on heating.

Answer

Element: Copper

Black Compound: Copper Oxide (CuO)

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Question 18

Why is paint applied on iron articles?

Solution

Paint prevents contact of iron with air and moisture and protects it from rusting.

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Question 19

Why are food items flushed with nitrogen?

Solution

Nitrogen prevents oxidation of oils and fats and avoids rancidity.

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Question 20

(a) Corrosion

Gradual destruction of metals by air and moisture.

Example:
Rusting of iron.

(b) Rancidity

Oxidation of fats and oils causing bad smell and taste.

Example:
Spoilage of chips and fried foods.

Common Mistakes

• Forgetting to balance equations.
• Confusing oxidation with reduction.
• Mixing displacement and double displacement reactions.
• Ignoring state symbols.
• Writing incorrect chemical formulae.

Exam Tips

• Learn all reaction types with examples.
• Practice balancing equations daily.
• Remember oxidation and reduction definitions.
• Revise important NCERT reactions.
• Focus on board-exam frequently asked questions.

Practice MCQs

1. Rusting of iron is an example of:
   A. Combination
   B. Corrosion
   C. Neutralization
   D. Sublimation

Answer: B

2. Which reaction releases heat?
   A. Endothermic
   B. Decomposition
   C. Exothermic
   D. Electrolysis

Answer: C

3. Whitewashing uses:
   A. CaO
   B. Ca(OH)₂
   C. CaCO₃
   D. MgO

Answer: B

4. Silver chloride decomposes in:
   A. Heat
   B. Water
   C. Sunlight
   D. Steam

Answer: C

5. Zn + CuSO₄ → ZnSO₄ + Cu is:
   A. Combination
   B. Displacement
   C. Reduction
   D. Neutralization

Answer: B

FAQ Section

Q1. What is a chemical reaction?
A. A process in which new substances are formed from reactants.

Q2. Why are chemical equations balanced?
A. To satisfy the law of conservation of mass.

Q3. What is oxidation?
A. Gain of oxygen or loss of hydrogen.

Q4. What is reduction?
A. Loss of oxygen or gain of hydrogen.

Q5. What causes rusting?
A. Reaction of iron with oxygen and moisture.

CTA (Call To Action)

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