Class 10 Science

Chapter 1 Solutions — Chemical Reactions and Equations

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Solutions

Overview

Step-by-step NCERT solutions for Chemical Reactions and Equations (Chapter 1, CBSE Class 10 Science) — every question and answer worked out in full, not just the final result. You can also read the Chemical Reactions and Equations textbook chapter.

Solved

What these solutions cover

All 24 questions in Chemical Reactions and Equations are solved in the PDF. Here's what's inside, exercise by exercise:

Chemical Equations and Balancing

Why should a magnesium ribbon be cleaned before burning in air?
2.
Write the balanced equation for the following chemical reactions:
- (i) Hydrogen gas combines with nitrogen to form ammonia.
- (ii) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
- (iii) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
- (iv) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Types of Chemical Reactions — Corrosion and Rancidity

Why do we apply paint on iron articles?
Oil and fat containing food items are flushed with nitrogen. Why?

Writing and Balancing Chemical Equations

A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black coloured compound formed.

Exercise

1.
Which of the following statements about the reaction below are incorrect? 2PbO(s) + C(s) → 2Pb(s) + CO₂(g)
- (a) Lead is getting reduced.
- (b) Carbon dioxide is getting oxidised.
- (c) Carbon is getting oxidised.
- (d) Lead oxide is getting reduced.
- (i) (a) and
- (b) (ii)
- (a) and
- (c) (iii) (a),
- (b) and
- (c) (iv) all
2.
Fe₂O₃ + 2Al → Al₂O₃ + 2Fe The above reaction is an example of a
- (a) combination reaction.
- (b) double displacement reaction.
- (c) decomposition reaction.
- (d) displacement reaction.
3.
What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer.
- (a) Hydrogen gas and iron chloride are produced.
- (b) Chlorine gas and iron hydroxide are produced.
- (c) No reaction takes place.
- (d) Iron salt and water are produced.
What is a balanced chemical equation? Why should chemical equations be balanced?
5.
Balance the following chemical equations:
- (a) HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O
- (b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O
- (c) NaCl + AgNO₃ → AgCl + NaNO₃
- (d) BaCl₂ + H₂SO₄ → BaSO₄ + HCl
6.
Write the balanced chemical equations for the following reactions:
- (a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
- (b) Zinc + Silver nitrate → Zinc nitrate + Silver
- (c) Aluminium + Copper chloride → Aluminium chloride + Copper
7.
Write the balanced chemical equation for the following and identify the type of reaction in each case:
- (a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
- (b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
- (c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
- (d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
What does one mean by exothermic and endothermic reactions? Give examples.
Why is respiration considered an exothermic reaction? Explain.
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity.
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
What do you mean by a precipitation reaction? Explain by giving examples.
15.
Explain the following in terms of gain or loss of oxygen with two examples each.
- (a) Oxidation
- (b) Reduction
A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black coloured compound formed.
Why do we apply paint on iron articles?
Oil and fat containing food items are flushed with nitrogen. Why?
19.
Explain the following terms with one example each:
- (a) Corrosion
- (b) Rancidity

Sample

Worked examples

3 questions from Chemical Reactions and Equations, solved step by step.

Chemical Equations and Balancing

Why should a magnesium ribbon be cleaned before burning in air?

Magnesium is a reactive metal. When stored in air, it reacts with oxygen and moisture to form a layer of magnesium oxide (MgO) on its surface.

This oxide layer is a white, dull coating that acts as a protective barrier and prevents the magnesium from burning properly.

Cleaning the ribbon with sandpaper removes this oxide layer, exposing the fresh, shiny metal surface underneath.

The clean surface ensures that magnesium burns readily and brightly in air, giving a proper demonstration of the combustion reaction:

2Mg + O₂ → 2MgO

Answer: The magnesium ribbon is cleaned to remove the protective layer of magnesium oxide (MgO) formed on its surface, which would otherwise prevent it from burning properly.

Types of Chemical Reactions — Corrosion and Rancidity

Why do we apply paint on iron articles?

Iron articles are painted to prevent them from rusting (corrosion).

When iron is exposed to moist air, it reacts with oxygen and water to form hydrated iron(III) oxide, commonly known as rust:

4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O (rust)

Paint forms a protective coating on the surface of iron, preventing the direct contact of iron with oxygen and moisture in the air.

Without this protective layer, the iron would gradually corrode, becoming weak and flaky, eventually damaging the article.

Answer: Paint is applied on iron articles to prevent rusting (corrosion) by forming a protective layer that keeps iron from direct contact with oxygen and moisture.

Writing and Balancing Chemical Equations

A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black coloured compound formed.

The shiny brown coloured element X is Copper (Cu).

When copper is heated in air, it reacts with oxygen to form copper(II) oxide, which is black in colour:

2Cu + O₂ → 2CuO

(brown) (black)

Verification: Cu = 2, O = 2 on both sides ✓

This is a combination reaction as well as an oxidation reaction (copper is oxidized by gaining oxygen).

Answer: Element X is Copper (Cu). The black coloured compound formed is Copper(II) oxide (CuO).

All 24 questions in Chemical Reactions and Equations are solved step by step in the Solutions PDF above.

Board papers

Chemical Reactions and Equations in CBSE board papers

Tested in 99 questions across 24 Class 10 board papers (2020–2026). Open a set to see exactly how this chapter is asked:

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Chapter 1 Solutions — Chemical Reactions and Equations

Overview

What these solutions cover

Chemical Equations and Balancing

Types of Chemical Reactions — Corrosion and Rancidity

Writing and Balancing Chemical Equations

Exercise

Worked examples

Why should a magnesium ribbon be cleaned before burning in air?

Why do we apply paint on iron articles?

A shiny brown coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black coloured compound formed.

Chemical Reactions and Equations in CBSE board papers

More solutions in Science

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