Important Questions for Class 10 Science Chapter 1 – Chemical Reactions and Equations

Chemical Reactions and Equations is the first chapter of Class 10 Science. It explains what a chemical reaction is, how reactions are written as balanced chemical equations, and the main types of reactions, such as combination, decomposition, displacement and double displacement reactions, along with oxidation, reduction, corrosion and rancidity.

CBSE Class 10 Science Chapter 1 important Question & Answers

Chemical Reactions and Equations
Medium
Q.
Which of the 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
Chemical Reactions and Equations
Medium
Q.
Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Chemical Reactions and Equations
Easy
Q.
Oil and fat containing food items are flushed with nitrogen. Why?
Chemical Reactions and Equations
Easy
Q.
Why do we apply paint on iron articles?
Chemical Reactions and Equations
Easy
Q.
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
Medium
Q.
Explain the following in terms of gain or loss of oxygen with two examples each.

(a) Oxidation
(b) Reduction
Chemical Reactions and Equations
Medium
Q.
What do you mean by a precipitation reaction? Explain by giving examples.
Chemical Reactions and Equations
Easy
Q.
In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Chemical Reactions and Equations
Medium
Q.
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Chemical Reactions and Equations
Medium
Q.
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Chemical Reactions and Equations
Medium
Q.
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.
Chemical Reactions and Equations
Easy
Q.
Why is respiration considered an exothermic reaction? Explain.
Chemical Reactions and Equations
Medium
Q.
What does one mean by exothermic and endothermic reactions? Give examples.
Chemical Reactions and Equations
Medium
Q.
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)
Chemical Reactions and Equations
Medium
Q.
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
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
Chemical Reactions and Equations
Medium
Q.
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
Chemical Reactions and Equations
Medium
Q.
Translate the following statements into chemical equations and then balance them.

(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Chemical Reactions and Equations
Medium
Q.
What is a balanced chemical equation? Why should chemical equations be balanced?
Chemical Reactions and Equations
Medium
Q.
What happens when dilute hydrochloric acid is added to iron fillings? 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.
Chemical Reactions and Equations
Medium
Q.
Explain the following terms with one example each.

(a) Corrosion
(b) Rancidity

Important Questions for Class 10 Science Chapter 1 - Chemical Reactions and Equations

These CBSE important questions cover displacement reactions, the reaction of iron with copper sulphate solution, rancidity, the preparation of copper sulphate crystals, the metal activity series and hydrolysis of salts. Every question has a clear answer with the chemical equations students need for the board exam.

CBSE Important Questions Class 10 Science – Chemical Reactions and Equations

Q1. What are displacement reactions? (1 mark)

Answer:

Reactions in which a more reactive element displaces a less reactive element from its salt solution are called displacement reactions. For example:

2KI (aq) + Cl₂ (g) → 2KCl (aq) + I₂ (s)

Q2. What is a chemical reaction? (1 mark)

Answer:

A chemical reaction is a process in which one set of substances (reactants) changes into new substances (products) by the breaking and forming of chemical bonds. For example, calcium oxide reacts with water to form calcium hydroxide.

Calcium oxide and water forming calcium hydroxide
Calcium oxide + water → calcium hydroxide

Q3. Rancidity of food materials (1 mark)

  1. cannot be prevented by using anti-oxidants
  2. can be prevented by packing fat and oil containing foods in nitrogen gas
  3. can be prevented by using air-packed puffy plastic bags
  4. will be more if kept in refrigerator

Answer:

(b) can be prevented by packing fat and oil containing foods in nitrogen gas.

Rancidity is caused by the oxidation of fats and oils. Nitrogen is an unreactive gas, so packing food in nitrogen keeps oxygen away and slows down rancidity.

Q4. When an iron nail is dipped in the aqueous solution of copper sulphate, the colour of the solution turns green. This green colour is due to (1 mark)

  1. displacement of Cu²⁺ ions by Fe²⁺ ions
  2. displacement of Cu⁺ ions by Fe²⁺ ions
  3. displacement of Fe²⁺ ions by Cu²⁺ ions
  4. displacement of Fe²⁺ ions by Cu⁺ ions

Answer:

(a) displacement of Cu²⁺ ions by Fe²⁺ ions.

Iron is more reactive than copper, so it displaces copper from copper sulphate. The solution turns green because iron sulphate (Fe²⁺ ions) is formed.

Q5. The reaction shown in the given figure is an example of (1 mark)

Iron nail dipped in copper sulphate solution before and after reaction
Iron nail in copper sulphate solution, before and after
  1. combination reaction
  2. displacement reaction
  3. oxidation reaction
  4. neutralisation reaction

Answer:

(b) displacement reaction.

Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s). Iron displaces copper from its salt solution.

Q6. What changes in colour of iron nails and copper sulphate solution do you observe after keeping the iron nails dipped in copper sulphate solution for about 30 minutes? (1 mark)

Answer:

The blue copper sulphate solution turns green because iron sulphate is formed, and a reddish-brown layer of copper is deposited on the grey iron nails.

Q7. Give an example each of the following types of displacement reactions: (a) metal displaces metal (b) non-metal displaces non-metal (5 marks)

Answer:

(a) A metal displaces another metal: zinc displaces copper from copper sulphate solution.

CuSO₄ (aq) + Zn (s) → ZnSO₄ (aq) + Cu (s)

(b) A non-metal displaces another non-metal: chlorine displaces bromine from potassium bromide solution.

2KBr (aq) + Cl₂ (g) → 2KCl (aq) + Br₂ (l)

Q8. Describe how crystals of copper sulphate are prepared. (5 marks)

Answer:

  • Take a cup of water in a beaker and add a few drops of dilute sulphuric acid to it.
  • Heat the water. When it starts boiling, add copper sulphate powder slowly while stirring continuously, until no more powder dissolves.
  • Filter the solution and allow it to cool.
  • Crystals of copper sulphate slowly form at the bottom of the beaker.

Q9. What happens when a piece of iron metal is placed in copper sulphate solution? (3 marks)

Answer:

A more reactive element displaces a less reactive element from its compound. Iron is more reactive than copper, so when a piece of iron is placed in copper sulphate solution, iron sulphate solution and copper metal are formed.

Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)

The blue solution turns green and a reddish-brown coating of copper forms on the iron.

Q10. Which type of reactions of metals are governed by their position in the metal activity series? (1 mark)

Answer:

Displacement reactions of metals are governed by their position in the activity series. A metal placed higher in the series can displace a metal placed below it from its salt solution.

Q11. Define hydrolysis. Explain with examples. (3 marks)

Answer:

Hydrolysis is a reaction in which a salt reacts with water to give an acidic or a basic solution. Salts formed from a strong acid and a weak base, or from a strong base and a weak acid, undergo hydrolysis.

  • Potassium carbonate is formed from a strong base and a weak acid. It hydrolyses to give potassium hydroxide and carbonic acid, so its solution is basic and turns red litmus blue.
  • Zinc sulphate is formed from a strong acid and a weak base. Its solution is acidic and turns blue litmus red.
Hydrolysis equations for potassium carbonate and zinc sulphate
Hydrolysis of potassium carbonate and zinc sulphate

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Q.4 The reaction shown in the given figure is an example of

(a) combination reaction

(b) displacement reaction

(c) oxidation reaction

(d) neutralisation reaction

Marks:1
Ans

In this reaction, iron displaces copper from its salt (copper sulphate). Therefore, it is a displacement reaction.

Q.5 The balanced chemical equation that represents the formation of barium sulphate from barium chloride solution and aluminum sulphate solution is

(a) BaCl2l+Al2SO43lBaSO4s+AlCl3l

(b) BaCl2 + Al2(SO4)3 BaSO4 + AlCl3

(c) 3BaCl2(aq)+Al2(SO4)3(aq)3BaSO

Marks:1

Ans

The chemical equation represented in option (c) correctly represents the reaction as it clearly indicates the physical states of all reactants and products and is also balanced.

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FAQs (Frequently Asked Questions)

Write three parts: (1) identify and name the reaction type, (2) write the balanced chemical equation with state symbols, and (3) give a one-line explanation of why it belongs to that category. This structure covers all three marks in most CBSE marking schemes.

Yes. HOTS questions from this chapter typically ask you to identify substances in multi-step scenarios, for example, a pale green substance heated to give brown residue and two gases, or a metal that forms black oxide but turns brown with hydrogen. The key is to apply your knowledge of specific reactions rather than recall them directly.

Balancing a chemical equation follows the Law of Conservation of Mass, which states that mass can neither be created nor destroyed in a chemical reaction. An unbalanced equation does not represent the actual reaction accurately. A balanced equation tells us the exact ratio in which reactants combine and products form.

Count how many substances change position. In displacement, one element moves and a single more reactive element pushes out a less reactive one. In double displacement, both compounds exchange ions and two new compounds form. If you see a precipitate forming from two solutions, it is almost always a double displacement reaction.

Yes. Balancing equations, identifying reaction types, and explaining corrosion or rancidity appear across almost every year’s board paper. Displacement and redox reaction questions with NCERT-style scenarios are also repeated regularly. Practising PYQs from the last five years gives strong coverage of what to expect.

Extramarks provides chapter-wise question banks with full solutions for Chemical Reactions and Equations. The page you are reading covers MCQs, short answers, long answers, PYQs, and a mini test paper with solutions, all aligned to the 2026-27 NCERT syllabus.