⚙ CBSE · Class 10 · Science · Chapter 1

Chemical Reactions
and Equations

Complete chapter resources for CBSE Class 10 Science — topic breakdown, key reaction types, sample questions, previous year board questions, and instant AI question paper generation.

4Topics
5–7Board marks
8Sample questions
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Key Concepts — Chapter 1
  • Combination: A + B → AB
  • Decomposition: AB → A + B (heat / light / electrolysis)
  • Displacement: A + BC → AC + B (A more reactive)
  • Double displacement: AB + CD → AD + CB (precipitate / gas)
  • Redox: oxidation + reduction occur simultaneously
  • Corrosion: 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O
Chapter Overview

What this chapter covers

Chapter 1 of CBSE Class 10 Science introduces the language of chemistry — the chemical equation. Students learn to write skeletal equations, apply the Law of Conservation of Mass, and balance equations using the hit-and-trial method, ensuring that the number of atoms of each element is equal on both sides. Physical states of reactants and products — solid (s), liquid (l), gas (g), and aqueous (aq) — as well as reaction conditions such as heat, light, or a catalyst are indicated above or below the arrow.

The chapter classifies chemical reactions into five types: combination, decomposition (thermal, electrolytic, and photolytic), displacement, double displacement, and oxidation-reduction (redox). Understanding these types helps students predict products and write balanced equations for unfamiliar reactions. Exothermic reactions release energy while endothermic reactions absorb it — a distinction frequently tested in board objective questions.

The chapter closes with two significant real-life applications of oxidation: corrosion (deterioration of metals, especially rusting of iron) and rancidity (oxidation of fats in food). Prevention methods — galvanisation, painting, oiling for corrosion; antioxidants, vacuum packing, refrigeration for rancidity — are standard 2-mark board questions and should be memorised with chemical reasoning, not just by rote.

Topics

What's inside Chapter 1

As per NCERT Class 10 Science (CBSE syllabus)

Topic 1
Chemical Equations and Balancing
Writing skeletal and balanced chemical equations. Law of Conservation of Mass. Hit-and-trial balancing method. Indicating physical states and reaction conditions (heat, catalyst, light).
Topic 2
Types of Chemical Reactions
Combination, decomposition (thermal / electrolytic / photolytic), displacement, and double displacement reactions — definitions, examples, and identifying reaction type from a given equation.
Topic 3
Oxidation and Reduction (Redox)
Oxidation as gain of oxygen or loss of hydrogen; reduction as loss of oxygen or gain of hydrogen. Simultaneous occurrence in redox reactions. Identifying oxidising and reducing agents.
Topic 4
Corrosion and Rancidity
Corrosion of metals (rusting of iron, tarnishing of silver, green patina on copper). Rancidity in fats and oils. Causes, effects, and prevention methods — antioxidants, galvanisation, vacuum packing.
Connections

How this chapter fits in

Useful for setting question difficulty and cross-chapter papers.

Builds on
Class 9 · Matter in Our Surroundings
Physical and chemical changes, states of matter
Class 9 · Atoms and Molecules
Atomic mass, molecular formulae, mole concept
Chapter 1 Chemical
Reactions
Leads to
Ch 2 · Acids, Bases and Salts
Neutralisation and double displacement reactions in solution
Ch 3 · Metals and Non-metals
Reactivity series, displacement reactions, metal extraction
Board Blueprint

Marks & question-type breakdown

Typical pattern based on CBSE Class 10 Science board papers from the last five years.

Question type Marks Typical count What's usually tested
MCQ / Objective 1 1–2 Identify reaction type, exo/endothermic, or oxidising agent
Very Short Answer 2 1 Balance a given equation or explain corrosion/rancidity with prevention
Short Answer 3 1 Classify a set of reactions or write balanced equations with conditions
Long Answer 5 0–1 Describe all types of decomposition with examples and balanced equations
Total (approximate) 5–7 3–5 Weightage varies across paper sets and years
Sample Questions

8 sample questions — generated by MarksZen AI

Aligned to CBSE Class 10 Science Chapter 1. Covers all question types across Easy, Medium, and Hard difficulty.

Q1 Easy 1 mark MCQ
Which of the following is a combination reaction? (a) 2H₂O → 2H₂ + O₂ (b) CaO + H₂O → Ca(OH)₂ (c) Fe + CuSO₄ → FeSO₄ + Cu (d) AgNO₃ + NaCl → AgCl + NaNO₃
Q2 Easy 2 marks Short Answer
Balance the following chemical equation: Fe + H₂O → Fe₃O₄ + H₂
Q3 Medium 2 marks Short Answer
What is a displacement reaction? Give one example with a balanced chemical equation.
Q4 Medium 3 marks Short Answer
Differentiate between exothermic and endothermic reactions. Give one example of each with a balanced chemical equation.
Q5 Medium 3 marks Short Answer
In the reaction: ZnO + C → Zn + CO (i) Identify which substance is oxidised and which is reduced. (ii) Name the oxidising agent and the reducing agent.
Q6 Hard 4 marks Short Answer
Describe the three types of decomposition reactions with one example and balanced equation for each. State the energy source involved in each type.
Q7 Hard 5 marks Long Answer
What is corrosion? Explain how iron rusts. Write the chemical equation for rusting. Name and explain any three methods used to prevent corrosion of iron.
Q8 Hard 5 marks Case-Based
A student observes a white precipitate forming when sodium sulphate solution is added to barium chloride solution. (i) Name the type of chemical reaction that has occurred. (ii) Write the balanced chemical equation for this reaction. (iii) What is the white precipitate formed? Is it soluble or insoluble in water? (iv) What are such reactions, in which a precipitate is formed, also called?
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Previous Year Questions

From CBSE board examinations

Actual questions from past Class 10 Science board papers — Chemical Reactions and Equations chapter.

Board 20222 marks
What is a double displacement reaction? Write a balanced chemical equation to represent a double displacement reaction. (All India 2022)
Board 20233 marks
Write balanced chemical equations for the following reactions: (a) Dilute sulphuric acid reacts with zinc granules. (b) Lead nitrate solution reacts with potassium iodide solution. (c) Calcium carbonate is heated strongly. (Delhi 2023)
Board 20205 marks
What is rancidity? Write two ways by which rancidity can be prevented. Also, explain with an example what is meant by an oxidation reaction. (CBSE 2020)
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FAQ

Questions teachers ask

How many marks does Chemical Reactions and Equations carry in the CBSE Class 10 board exam? +
Typically 5–7 marks across 3–4 questions — one 1-mark MCQ, one 2-mark short answer on balancing or identifying reaction type, and one 3–5 mark question on corrosion/rancidity or explaining observations with equations. This chapter is one of the highest-yield chapters in the CBSE Class 10 Science paper.
How do you balance a chemical equation step by step for board exams? +
Follow the hit-and-trial method: (1) write the skeleton equation with correct formulae, (2) count atoms of each element on both sides, (3) place coefficients (never change subscripts) to equalise atoms starting with the most complex molecule, (4) verify the final count, and (5) indicate physical states (s), (l), (g), (aq) and conditions (heat arrow, catalyst) for full marks. CBSE awards 1 mark for each correctly placed coefficient in multi-step balancing questions.
What are the five types of chemical reactions students must know for CBSE Class 10? +
The five types are: (1) Combination reaction — two or more substances combine to form a single product; (2) Decomposition reaction — a single reactant breaks into two or more products (thermal, electrolytic, or photolytic); (3) Displacement reaction — a more reactive element displaces a less reactive one from its salt solution; (4) Double displacement reaction — ions of two compounds exchange partners, often forming a precipitate; (5) Oxidation-reduction (redox) reaction — simultaneous transfer of oxygen/hydrogen or electrons.
What is the difference between corrosion and rancidity, and why does CBSE ask about them? +
Corrosion is the slow deterioration of metals by reaction with atmospheric oxygen, moisture, or acids (e.g., rusting of iron: 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O). Rancidity is the oxidation of fats and oils in food, producing unpleasant smell and taste. Both are real-life applications of oxidation and are explicitly listed as NCERT examples. Board questions typically ask students to explain the process, give one example, and name one prevention method — making them reliable 2-mark targets.
How do I generate a custom question paper for Chemical Reactions and Equations using MarksZen? +
Sign up for a free MarksZen account, choose CBSE Class 10 Science, select Chapter 1 (Chemical Reactions and Equations), set your preferred question-type mix (MCQ, short answer, long answer) and total marks — the AI generates a complete board-aligned paper with answer key in under 2 minutes, ready for PDF export.