Class 10 · NCERT Science

Chapter 1

Chemical Reactions and Equations

Balance equations and identify reaction types, oxidation, and reduction. Learn the ideas, see how they connect, and practise until you can choose the next step without help.

BalancingReaction typesRedox

Reviewed by Eduro educators · Built for independent practice

Study board

Quick reference
Concept 01Balancing
Concept 02Reaction types
Concept 03Redox

NCERT chapter notes

Chemical Reactions and Equations, clearly explained

This chapter introduces chemical equations and how to balance them using the law of conservation of mass, then classifies reactions into combination, decomposition, displacement, and double displacement, and explains oxidation and reduction (redox).

It ends with two everyday effects of oxidation — corrosion (rusting of iron) and rancidity (spoiling of oily food) — which are common one- and two-mark questions.

Core concepts

Key concepts and formulae

01

Balancing a chemical equation

A balanced equation has the same number of atoms of each element on both sides, following the law of conservation of mass. For example, Fe + H₂O → Fe₃O₄ + H₂ balances to 3Fe + 4H₂O → Fe₃O₄ + 4H₂.

02

Combination reaction

Two or more substances combine to form a single product, e.g. CaO + H₂O → Ca(OH)₂. This reaction releases heat, so it is exothermic.

03

Decomposition reaction

A single compound breaks into two or more substances using heat (thermal, e.g. CaCO₃ → CaO + CO₂), light (photochemical, e.g. 2AgCl → 2Ag + Cl₂), or electricity (electrolytic). These are usually endothermic and are the opposite of combination reactions.

04

Displacement and double displacement

In displacement, a more reactive element displaces a less reactive one, e.g. Fe + CuSO₄ → FeSO₄ + Cu. In double displacement, ions are exchanged, often forming a precipitate, e.g. BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl.

05

Oxidation and reduction (redox)

Oxidation is gain of oxygen or loss of hydrogen/electrons; reduction is loss of oxygen or gain of hydrogen/electrons. In CuO + H₂ → Cu + H₂O, CuO is reduced to Cu and H₂ is oxidised to H₂O.

06

Corrosion and rancidity

Corrosion is the slow eating away of a metal by air and moisture (rusting of iron). Rancidity is the oxidation of fats and oils in food, giving a bad smell and taste; it is slowed by antioxidants, airtight packing, and flushing packets with nitrogen.

Exam practice

Important questions, with worked answers

Use each answer to check the method and wording—not as a paragraph to memorise.

Q1Balance the equation: Fe + H₂O → Fe₃O₄ + H₂.

Answer

3Fe + 4H₂O → Fe₃O₄ + 4H₂.

Q2Why is respiration considered an exothermic reaction?

Answer

During respiration, glucose combines with oxygen and breaks down to release energy (as ATP). Since energy is released, respiration is an exothermic reaction.

Q3Identify the substances oxidised and reduced in: CuO + H₂ → Cu + H₂O.

Answer

CuO loses oxygen, so it is reduced to Cu. H₂ gains oxygen, so it is oxidised to H₂O.

Q4Why do we apply paint on iron articles?

Answer

Paint forms a protective layer that prevents iron from coming into contact with air and moisture, thereby preventing rusting (corrosion).

Q5Why are food items containing fats and oils flushed with nitrogen before sealing?

Answer

Nitrogen is an unreactive gas; it removes oxygen from the packet and prevents the oxidation of fats and oils, thus preventing rancidity.

Q6Define a decomposition reaction with an example, and explain why it is called the opposite of a combination reaction.

Answer

A decomposition reaction is one in which a single compound breaks into two or more simpler substances, e.g. CaCO₃ → CaO + CO₂. It is the opposite of combination because combination joins substances into one, while decomposition splits one into many.

Q7What is observed when an iron nail is dipped in copper sulphate solution? Write the equation.

Answer

The blue colour of copper sulphate fades and a brownish copper deposit forms on the nail, because iron (more reactive) displaces copper: Fe + CuSO₄ → FeSO₄ + Cu.

Fast recall

Key terms to remember

Balanced equation: Equation with equal numbers of each kind of atom on both sides (conservation of mass).

Exothermic reaction: Reaction that releases heat energy to the surroundings.

Precipitate: Insoluble solid formed in a double displacement reaction.

Corrosion: Gradual damage of a metal by reaction with air and moisture, e.g. rusting.

Rancidity: Oxidation of fats and oils in food, producing a bad smell and taste.

A repeatable method

How to learn Chemical Reactions and Equations properly

  1. 1

    Start with the chapter promise

    Balance equations and identify reaction types, oxidation, and reduction. Before solving, the student should be able to say what the chapter is trying to teach and which kind of problem it helps solve.

  2. 2

    Build the core vocabulary

    The important words for this chapter are Balancing, Reaction types and Redox. Eduro should make the student define each one in simple language, then use it in a question or explanation.

  3. 3

    Move from recognition to recall

    Recognition means the answer makes sense after seeing it. Recall means the student can produce the next step independently. This page is built for recall, because that is what tests reward.

  4. 4

    Close the loop with practice

    A strong study session ends with concept and diagram practice, not only reading. The student should solve, review the mistake, and then attempt a similar question before moving on.

Before the test

Where students usually lose marks

Look for the first wrong decision—not only the final wrong answer. That is the mistake worth repairing.

Mistake 1

Knowing Balancing only after seeing the solution

This is the most common hidden gap. The student feels confident while reading, but cannot choose the starting step alone. Eduro should ask a short diagnostic question before explaining the method.

Mistake 2

Treating Chemical Reactions and Equations as a memory chapter

Even memory-heavy chapters need reasoning. A memorised line becomes fragile when the question changes. The student should explain why the answer works, not only what the answer is.

Mistake 3

Skipping the checking step

concept-to-example gap usually survives because the student finishes the answer and moves on. Eduro should make review part of the answer: what was asked, what was used, and whether the final response fits.

Try it with Eduro

Practice that builds real confidence

Say it naturally, as you would to a patient teacher. Each prompt below is designed to make understanding visible.

Prompt 1

Ask Eduro to explain Chemical Reactions and Equations through Balancing before showing any solved answer.

Prompt 2

Create five questions that separately test Balancing, Reaction types and Redox.

Prompt 3

Give one wrong answer from Chemical Reactions and Equations and ask the student to find the first incorrect step.

Prompt 4

End with a mixed mini-test where Eduro does not reveal which skill is being tested.

For parents

A better way to ask, “Is the chapter done?”

For Class 10 Science, a good sign is not that the child says 'Chemical Reactions and Equations is done.' A better sign is that they can explain Balancing, solve one fresh question, and correct one mistake without panic.

Created by

Eduro Editorial Team

CBSE learning research and AI tutoring design

Reviewed by

Eduro Academic Review

Curriculum and accuracy review

Freshness

Reviewed for the 2025-26 CBSE/NCERT study cycle

Reviewed quarterly and after major CBSE/NCERT updates

Quick help

Common questions

How can I study Chemical Reactions and Equations for NCERT Class 10?

Start with the NCERT examples, understand the key ideas in Balancing, Reaction types, Redox, then practice exercise questions and ask Eduro where you get stuck.

Can Eduro help with Chemical Reactions and Equations?

Yes. Eduro can explain Chemical Reactions and Equations step by step, answer follow-up doubts, and help students practice related Science questions.