Chemical Reactions & Eq. Important Questions Class 10 2026

Chemical Reactions and Equations is the first chapter of Class 10 Science, and one of the most scoring ones. It introduces you to how substances change into new forms, through reactions that happen all around us, from the rusting of iron to digestion in our bodies.

In this chapter, you learn not just to identify different types of reactions, but to balance equations, classify reaction types, and understand real-life chemical processes. The chapter also builds the foundation for advanced topics you’ll study in Class 11 and 12 Chemistry, such as redox reactions and electrochemistry.

This set of Class 10 Chemical Reactions and Equations Important Questions helps you:

• Practise all exam-focused reaction types.
• Strengthen your understanding of balancing equations.
• Prepare confidently for both CBSE board exams and school tests.

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(Most Important Questions of this Chapter from our 📕) 

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In the table below, we have provided the links to downloadable PDFs for Extra Questions For Class 10 Science Chapter 1 with Answers. Now you can download them without requiring a login.

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Chapter 1 Chemical Reactions and Equations Important Questions

When steam is passed through red hot iron, iron oxide and hydrogen gas is formed. The balanced equation for the reaction is shown below.

3Fe + 4H₂O  → Fe₃O₄ + 4H₂‍

(iron)   (water)      (iron oxide) (hydrogen)

Q1. Is heating iron to red hot a physical or a chemical change? Explain your answer. 

Ans. Heating iron to red hot is a physical change as no new substance is formed. 

Explanation

Iron changes color and softens when heated, but its chemical composition doesn't change. This is due to the absence of any new substance formation or chemical reaction.

The change is reversible and temporary. Once the iron cools, it returns to its original state.

A physical change affects the physical properties of a substance, such as shape, size, color, and condition, without altering its chemical structure.

Q2. What is true for the balanced chemical equation shown above?

1. Four atoms of water combine with iron to form four atoms of hydrogen. What is true for the balanced chemical equation shown above? 

2. Three atoms of iron combine with water to form four atoms of hydrogen. 

3. Four molecules of water combine with iron to form an atom of iron oxide. 

4. Three atoms of iron combine with water to form one molecule of iron oxide. 

Ans. (b)Three atoms of iron combine with water to form one molecule of iron oxide.  (B)

‍Explanation:

 Iron reacts with water to form iron oxide and hydrogen gas. This process is called rusting. The iron oxide forms a brown layer on the iron.

Cellular respiration is a chemical process by which cells convert glucose to energy. The equation given below shows the reaction for cellular respiration.  

C₆H₁₂O₆ + 6O₂→ 6CO₂ + 6H₂O + Energy

Q3. In the above reaction, which substance is oxidised?

Ans.  Glucose is oxidized. 

Explanation

‍Glucose is a carbohydrate, or sugar, that the body uses to provide energy to tissues and structures. However, the body can't use glucose in its raw form, so it must be broken down through a process called cellular respiration.

Q4. Carbon dioxide and water are the two new substances formed during cellular respiration. What are they known as?

1. Reactants

2. Mixtures

3. Catalysts

4. Products

Ans.

‍(d) Products‍

Explanation

‍Cellular respiration is a process that extracts energy from glucose and oxygen to produce carbon dioxide, water, and adenosine triphosphate (ATP). The reactants of cellular respiration are glucose and oxygen, while the products are carbon dioxide, water, and ATP. The overall chemical reaction for cellular respiration is glucose + oxygen → carbon dioxide + water.

A piece of magnesium ribbon is added to a flask containing dilute hydrochloric acid.  Hydrogen gas is formed which is collected in the measuring cylinder.  The amount of hydrogen formed with time is plotted on a graph.   The line on the graph indicates the rate of chemical reaction occurring in the flask.

Q5. At what time is the reaction rate the fastest in the flask?

1. At 1 minute 
2. At 3 minutes
3. At 4 minutes 
4. At 6 minutes

Ans.

‍(a) At 1 minute

‍Explanation: 

‍The reaction rate between magnesium and dilute hydrochloric acid is fastest at the beginning of the reaction, around 1 minute. This is because the amount of magnesium is at its highest at the start, which allows the reaction to proceed more rapidly. As the magnesium is consumed, the rate of the reaction gradually decreases.

Q6. The reaction is repeated with magnesium powder in place of magnesium ribbon under the same conditions. Will the reaction rate increase or decrease?

Explain your answer with reference to the volume of hydrogen formed in the flask at 2 minutes.

Ans.

‍The reaction rate will increase and therefore the volume of hydrogen formed at 2 minutes will be higher. 

‍Explanation

‍This is because magnesium powder has a larger surface area than magnesium ribbon, which allows more reactant particles to be exposed to the acid. This leads to more collisions between reactants and a faster reaction rate.

Q7. Which of these could increase the rate of reaction in the flask? Circle ‘Yes’ or ‘No’ for each row. 

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Ans. Yes!!

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Explanation: 

All three factors will increase the rate of reaction when magnesium ribbon is added to hydrochloric acid (HCl):

1. Adding more acid to the flask: This increases the concentration of H⁺ ions in the solution, enhancing the chances of magnesium particles colliding with H⁺ ions, thereby increasing the reaction rate.

2. Heating the acid in the flask: Raising the temperature increases the kinetic energy of the particles, causing them to move faster and collide with greater force. This leads to a higher rate of reaction.

3. Using a higher concentration of acid: A higher concentration of HCl increases the number of H⁺ ions in the solution, which boosts the frequency of collisions between magnesium particles and H⁺ ions, accelerating the reaction.

Q8. Magnesium reacts with hydrochloric acid to form magnesium chloride and hydrogen gas.  Write a balanced chemical equation to show the reaction. 

Ans.

‍Mg + 2HCl → MgCl₂ + H₂

_‍Explanation:

‍Magnesium is more reactive than hydrogen and displaces it in the chloride molecule.

Q9. Which of these is an example of decomposition reaction?

1. Melting of glaciers 
2. Rusting of old bridges 
3. Rotting of fruits and vegetables 
4. Absorption of carbon dioxide by oceans

Ans.

‍(c) Rotting of fruits and vegetables. 

‍Explanation:

‍A decomposition reaction is a chemical reaction in which a single reactant breaks down into two or more products. In the case of rotting fruits and vegetables, the organic matter undergoes decomposition, breaking down into simpler substances.

Q10. Methane gas released from waste water treatment plants can be used as a source of fuel. Which chemical equation represents combustion of methane to produce heat energy?

A. CH₄ + CO₂→ 2O₂ + 2H₂O 

B. CH₄ + 2O₂→ CO₂ + 2H₂O 

C. 2O₂ + 2H₂O → CO₂ + CH₄ 

D. CO₂ + 2O₂→ CH₄ + 2H₂O 

Ans. 

‍(b) CH₄ + 2O₂→ CO₂ + 2H₂O

‍Explanation:

The reaction releases heat energy, making methane a valuable source of fuel. Therefore, the correct answer is (b) CH₄ + 2O₂→ CO₂ + 2H₂O

Some more Important Questions for class 10

Q1. What happens when ferrous sulphate crystals are heated? Write the balanced chemical equation and the observations.

Ans. When green coloured ferrous sulphate crystals (FeSO₄·7H₂O) are heated in a dry boiling tube, they undergo decomposition.

Observations:

1. The green colour of the crystals fades.
2. They turn brown due to the formation of ferric oxide (Fe₂O₃).
3. A pungent smell of burning sulphur is noticed.
4. Brown fumes of sulphur dioxide (SO₂) and sulphur trioxide (SO₃) are released.

Reaction: 2FeSO₄ (s) ------heat-------> Fe₂O₃ (s) + SO₂ (g) + SO₃ (g)

This is a thermal decomposition reaction.

Q2. Why is a magnesium ribbon cleaned before burning? Write the balanced chemical equation for its burning.

Ans. Magnesium ribbon, when exposed to air, develops a thin white coating of magnesium oxide. This layer prevents the magnesium from burning easily.

Hence, the ribbon is rubbed with sandpaper before burning to remove the oxide layer and expose fresh magnesium surface.

When burnt in oxygen, magnesium burns with a dazzling white flame to form magnesium oxide. 

Q3. Write an activity to show that hydrogen gas is evolved when zinc reacts with dilute sulphuric acid.

Ans. Here are the activities to show that  hydrogen gas is evolved when zinc reacts with dilute sulphuric acid.

1. Place some zinc granules in a conical flask.
2. Add dilute H₂SO₄ → bubbles appear due to gas evolution.
3. Fit the flask with a cork and delivery tube. Collect the gas in a soap solution.
4. Bring a burning matchstick near one of the bubbles. It bursts with a pop sound.

Observations:

• Effervescence is seen.
• The flask becomes warm (exothermic reaction).
• Pop sound confirms hydrogen gas.

Equation:

Zn(s)+H2​SO4​(aq)→ZnSO4​(aq)+H2​(g)

Conclusion: Hydrogen gas is released when zinc reacts with dilute sulphuric acid.

Q4. What happens when ferrous sulphate crystals are heated? Mention the observations and write the equation.

Ans. Green crystals of ferrous sulphate (FeSO₄·7H₂O) decompose when heated strongly.

Observations:

• Green colour changes to brown (ferric oxide).
• Pungent smell of SO₂ and SO₃ gases.

Equation: 2FeSO4​​→Fe2​O3​+SO2​+SO3

Q5. What change is observed when silver chloride is kept in sunlight? Write the reaction.

Ans.  White silver chloride decomposes in sunlight to form grey silver and chlorine gas.

Reaction: 2AgCl→2Ag+Cl2​

This is a photochemical decomposition reaction.

Q6. Explain with an activity what happens when an iron nail is dipped in copper sulphate solution.

Ans. Here is the activity that happens when an iron nail is dipped in copper sulphate solution.

1. Take two test tubes containing blue copper sulphate solution.
2. Dip a clean iron nail into one test tube. Keep the other as control.
3. Leave for 20 minutes.

Observations:

• The blue colour of CuSO₄ solution fades.
• A reddish-brown deposit forms on the iron nail.

Equation: Fe+CuSO4​→FeSO4​+Cu

Explanation: Iron, being more reactive than copper, displaces copper from its solution. The solution turns greenish (FeSO₄), and copper metal is deposited.

This is a displacement reaction.

Q7. Write a balanced equation for the electrolysis of water. Why is dilute sulphuric acid added?

Ans. Electrolysis of water produces hydrogen and oxygen gases.

Equation: 2H2​O​​→2H2​+O2​

• Hydrogen is collected at the cathode, oxygen at the anode.
• The volume of hydrogen is double that of oxygen.
• Dilute H₂SO₄ is added to increase conductivity of water.

Q8. Define rancidity. How can it be prevented?

Ans. Rancidity is the spoilage of food containing oils and fats when they get oxidised. The food develops a foul smell and bad taste.

Prevention methods:

1. Storing in airtight containers.
2. Flushing packets with nitrogen gas (e.g., chips packets).
3. Refrigeration.
4. Adding antioxidants.

Q9. What is observed when copper powder is strongly heated in air? How can the black coating be changed back to copper?

Ans When copper powder is strongly heated in air: The reddish-brown copper surface turns black due to copper(II) oxide (CuO).

Equation:

2Cu+O2​→2CuO

Now, pass hydrogen gas over the hot black CuO:

CuO+H2​→Cu+H2​O

Observations:

• Black coating disappears.
• Copper regains its reddish-brown colour.

This proves the concepts of oxidation (copper → CuO) and reduction (CuO → copper).

Q10. Write the chemical equation for the decomposition of calcium carbonate. Name the products formed.

Ans. CaCO3​—CaO+CO2​

Products: Quick lime (CaO) and carbon dioxide.

Q11. Why is respiration considered an exothermic process? Write the equation.

Ans. Respiration is the process of breaking down glucose molecules inside cells to release energy.

Explanation:

• Glucose reacts with oxygen inside cells.
• It produces CO₂, H₂O, and a large amount of energy.
• This energy is used for daily life processes like muscle movement, repair, and growth.

Equation: C6​H12​O6​+6O2​→6CO2​+6H2​O+Energy

Since energy is released, respiration is an exothermic reaction.

Q12. Explain the term corrosion with an example.

Ans. Corrosion is the slow destruction of metals due to reaction with air, water, or chemicals.

Example: Rusting of iron.

4Fe+6H2​O+3O2​→4Fe(OH)3​→Fe2​O3​⋅xH2​O

This weakens iron objects like gates, bridges, and ships.

Q13. Why does a matchstick produce flame only after rubbing it on the side of the box?

Ans. The match head contains antimony sulphide and potassium chlorate. The side of the matchbox has red phosphorus. When rubbed, friction converts red phosphorus to white phosphorus, which ignites easily and lights the match.

Q14. Write the chemical equation for the reaction between quick lime and water. Name the type of reaction.

Ans. CaO+H2​O→Ca(OH)2​+Heat

Type: Combination reaction (also exothermic)

Q15. Give one example each of:

(a) Precipitation reaction
(b) Neutralisation reaction

Ans.
(a) AgNO₃ + NaCl → AgCl ↓ + NaNO₃
(b) HCl + NaOH → NaCl + H₂O

Q16. Explain with an example what a displacement reaction is.

Ans: A displacement reaction is one where a more reactive element displaces a less reactive element from its compound.

Example:

Zn+CuSO4​→ZnSO4​+Cu

Thus as we can see through this activity, Here, zinc (more reactive) displaces copper from CuSO₄.

Q17. What are exothermic and endothermic reactions? Give one example each.

Ans.

• Exothermic reaction: Heat is released. Example: CH₄ + 2O₂ → CO₂ + 2H₂O + Heat
• Endothermic reaction: Heat is absorbed. Example: CaCO₃ → CaO + CO₂

Q18. What happens when lead nitrate is heated? Mention observations.

Ans: Lead nitrate decomposes on heating: 2Pb(NO3​)2​→2PbO+4NO2​+O2​

Observations:

• Yellow PbO residue.
• Brown fumes of NO₂.
• Oxygen gas releases

Q19. Explain why corrosion is a redox reaction using rusting of iron.

Ans.
Rusting involves both oxidation and reduction:

• Iron loses electrons (oxidation): Fe→Fe2++2e−
• Oxygen in water gains electrons (reduction): O2​+4e−+2H2​O→4OH−
• The final product is hydrated ferric oxide (rust): Fe2​O3​⋅xH2​O

Thus we can see, since oxidation (iron) and reduction (oxygen) occur simultaneously, rusting is a redox reaction.

Q20. Translate into a chemical equation:

Barium chloride reacts with aluminium sulphate to give aluminium chloride and barium sulphate.

Ans. 3BaCl2​+Al2​(SO4​)3​→2AlCl3​+3BaSO4​↓

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Video Lecture: Must-watch for Quick Revision

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Extra Questions for Practice – Challenge Yourself! 

Q1. Why does the colour of copper sulphate solution change when an iron nail is dipped into it?

Q2. Write a balanced chemical equation for the decomposition of lead nitrate. What do you observe during the reaction?

Q3. Why is photosynthesis considered the reverse of respiration? Explain with equations.

Q4. Define precipitation reaction. Give two daily life examples where such reactions are useful.

Q5. State two differences between a displacement and a double displacement reaction with examples.

Q6. Why is it important to store chips in air-tight, nitrogen-flushed packets? Name the chemical process involved.

Q7. Write the balanced chemical equations for the following reactions:

(a) Action of heat on zinc carbonate
(b) Action of electricity on molten sodium chloride

Q8. How can rusting of iron be prevented? Mention any three methods.

Q9. A shining greyish metal ‘X’ is added to blue copper sulphate solution. The blue colour slowly fades and a reddish deposit forms on the metal.

(a) Identify metal ‘X’.
(b) Write the balanced chemical equation.
(c) Name the type of reaction.

Q10. Why are state symbols (s, l, g, aq) important while writing a chemical equation? Illustrate with an example.

Why is this Chapter Important?

Chemical reactions and equations are fundamental concepts in chemistry that demonstrate how matter interacts and transforms. Mastering this chapter enables students to:

• Identify different types of chemical reactions.
• Balance chemical equations.
• Predict products of reactions.
• Understand practical applications like corrosion, rancidity, and more.

Study Tips for the Chapter

Understand the Core Principles: Grasp the concepts of reactants, products, and reaction conditions. Learn why and how reactions occur.

Practice Balancing Equations: Start with simple equations and gradually move to complex ones. Balancing equations strengthens your understanding of reaction stoichiometry.

Use Mnemonics for Reaction Types: Develop short phrases or keywords to remember reaction types and examples.

Make a Reaction Chart: Create a chart categorising reactions with their equations, characteristics, and examples. This will aid in quick revision.

Relate to Daily Life: Observe real-life chemical reactions, like cooking, cleaning, or using batteries, and connect them to the chapter's content.

Common Mistakes to Avoid

Ignoring State Symbols: Always include the physical states of reactants and products (solid (s), liquid (l), gas (g), or aqueous (aq)) in equations.

Skipping Steps in Balancing: Many students skip intermediate steps while balancing equations, leading to errors. Write each step clearly.

Confusing Reaction Types: Practice multiple examples of each reaction type to avoid confusion during exams.

FAQs

Q1. How many marks are generally asked from this chapter in Class 10 Science exams?

Ans.  Usually, 3–5 marks worth of questions come from this chapter, often including one reaction-based or application-based question.

Q2. How can I easily remember the types of reactions?

Ans.  Associate each type with an example , for example, burning of magnesium (combination), electrolysis of water (decomposition), and zinc + copper sulphate (displacement). Linking examples to each reaction type helps retain them longer.

Q3. Are equations given in NCERT enough for exams?

Ans.  Yes. Almost all board questions are derived from NCERT examples and activities. Just ensure you understand them instead of rote learning.

Q4. What is the most common mistake students make in this chapter?

Ans. Forgetting to balance equations correctly or missing physical states (like (s), (l), (g), (aq)) in the final answer. CBSE deducts marks for incomplete notation.

Q5. How should I prepare for practical or case-based questions related to this topic?

Ans.Read experiments from the Activities section of NCERT carefully , for example, the reaction of magnesium ribbon with hydrochloric acid. Know the observation (like gas evolution, colour change, or precipitate formation).