Chemical Reactions and Equations
INTRODUCTION:
Ever wondered why a cut apple turns brown, why milk becomes sour when left outside, or why fireworks create colorful explosions in the sky? All these everyday miracles happen because of chemical reactions ! Chapter 1 of your Class 10 Science syllabus unlocks the secrets behind these transformations and teaches you the language chemists use to describe them. Whether you're searching for class 10 chemical reactions and equations notes, class 10 chemical reactions and equations MCQ, or class 10 chemical reactions and equations important questions, this complete guide will make chemistry easy, interesting, and exam-ready for your CBSE Board 2026. Let's turn those confusing equations into simple formulas for success!
What is a Chemical Reaction?
A chemical reaction
is a process where one or more substances (reactants) change into new
substances (products) with different properties.
Characteristics of Chemical Reactions:
· Change in color – Iron turns reddish-brown when it rusts
· Change in temperature – Burning of coal releases heat
· Formation of gas – Bubbles form when zinc reacts with acid
· Formation of precipitate – White solid forms when silver nitrate mixes with sodium chloride
· Change in state – Solid ice melts to liquid water
Chemical Equations
A chemical equation represents a chemical reaction using symbols and formulas. It shows reactants on the left side and products on the right side, separated by an arrow.
Example:
Zinc reacts with sulfuric acid to form zinc sulfate and hydrogen gas.
Word
Equation:
Zinc + Sulfuric Acid → Zinc Sulfate + Hydrogen
Chemical
Equation:
Zn + H₂SO₄ → ZnSO₄ + H₂
Balanced Chemical Equations
A balanced chemical equation has equal numbers of atoms of each element on both sides. This follows the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a chemical reaction.
Why Balance Chemical Equations?
Balancing ensures that the total mass of reactants equals the total mass of products.
How to Balance Chemical Equations:
Step
1: Write the
unbalanced equation
Step 2:
Count atoms of each element on both sides
Step 3:
Add coefficients to balance atoms
Step 4:
Verify that all atoms are balanced
Example:
Unbalanced: Fe + H₂O → Fe₃O₄
+ H₂
Balanced:
3Fe + 4H₂O →
Fe₃O₄ + 4H₂
|
Element |
Reactants |
Products |
|
Fe (Iron) |
3 |
3 |
|
H (Hydrogen) |
8 |
8 |
|
O (Oxygen) |
4 |
4 |
Types of Chemical Reactions
Chemical reactions are classified into five main types:
1. Combination Reaction
Two or more reactants combine to form a single product.
General Form: A + B → AB
Example:
CaO + H₂O →
Ca(OH)₂
(Calcium oxide + Water → Calcium hydroxide)
When calcium oxide (quick lime) reacts with water, it produces slaked lime and releases heat. This is also an exothermic reaction.
2. Decomposition Reaction
A single reactant breaks down into two or more products.
General Form: AB → A + B
Types of Decomposition:
·
Thermal
Decomposition
(heat required)
2FeSO₄ →
Fe₂O₃ + SO₂ + SO₃
·
Electrolytic
Decomposition
(electricity required)
2H₂O →
2H₂ + O₂
·
Photolytic
Decomposition
(light required)
2AgCl → 2Ag + Cl₂
3. Displacement Reaction
A more reactive element displaces a less reactive element from its compound.
General Form: A + BC → AC + B
Example:
Zn + CuSO₄ →
ZnSO₄ + Cu
(Zinc + Copper sulfate → Zinc sulfate + Copper)
Zinc is more reactive than copper, so it displaces copper from copper sulfate solution. The blue color of copper sulfate fades.
4. Double Displacement Reaction
Two compounds exchange ions to form two new compounds.
General Form: AB + CD → AD + CB
Example:
Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
(Sodium sulfate + Barium chloride → Barium sulfate + Sodium chloride)
Barium sulfate (BaSO₄) forms as a white precipitate. Reactions that produce precipitates are called precipitation reactions.
5. Oxidation and Reduction (Redox Reactions)
Oxidation is the gain of oxygen or loss of hydrogen.
Reduction
is the loss of oxygen or gain of hydrogen.
Example:
CuO + H₂ →
Cu + H₂O
· Copper oxide (CuO) loses oxygen → Reduction
· Hydrogen (H₂) gains oxygen → Oxidation
Both
oxidation and reduction occur together in a redox reaction.
Visualising the Nation - Complete NCERT Notes.
Effects of Oxidation in Daily Life
1. Corrosion
When metals react with oxygen, moisture, and acids, their surface gets corroded.
Example: Rusting of iron
4Fe + 3O₂ + xH₂O → 2Fe₂O₃.xH₂O (rust)
2. Rancidity
When fats and oils are oxidized, they become rancid and their smell and taste change.
Prevention methods:
· Store food in airtight containers
· Add antioxidants
· Keep food in refrigerator
· Use nitrogen gas in packaging
Short Notes
· Chemical Reaction: Process where substances transform into new substances
· Reactants: Starting materials in a reaction
· Products: New substances formed in a reaction
· Balanced Equation: Equal atoms on both sides
· Law of Conservation of Mass: Mass remains constant in reactions
· Exothermic Reaction: Releases heat (Example: burning, respiration)
· Endothermic Reaction: Absorbs heat (Example: photosynthesis)
· Precipitate: Insoluble solid formed in a reaction
· Combination: A + B → AB
· Decomposition: AB → A + B
· Displacement: A + BC → AC + B
· Double Displacement: AB + CD → AD + CB
The Making of Germany and Italy - Section 4 Complete Notes
MCQs for Practice (CBSE Board PYQs)
1.
Sodium reacts with water to form sodium hydroxide and hydrogen gas. The
balanced equation is:
[CBSE 2021-22]
(a) Na(s) + 2H₂O(l) →
2NaOH(aq) + 2H₂(g)
(b) 2Na(s) + 2H₂O(l) →
2NaOH(aq) + H₂(g)
(c) 2Na(s) + 2H₂O(l) →
NaOH(aq) + 2H₂(g)
(d) 2Na(s) + H₂O(l) →
2NaOH(aq) + 2H₂(g)
Answer: (b)
2.
It is important to balance chemical equations to satisfy the law of
conservation of mass. Which statement is incorrect? [CBSE 2021-22]
(a) The total mass of elements in reactants equals the total mass in products
(b) The number of atoms of each element remains the same before and after
reaction
(c) The chemical composition of reactants is the same before and after the reaction
(d) Mass can neither be created nor destroyed in a chemical reaction
Answer: (c)
3. When
aqueous solutions of potassium iodide and lead nitrate are mixed, an insoluble
substance separates out. The correct equation is: [CBSE 2023]
(a) KI + PbNO₃ →
PbI + KNO₃
(b) 2KI + Pb(NO₃)₂ → PbI₂ + 2KNO₃
(c) KI + Pb(NO₃)₂ → PbI + KNO₃
(d) KI + PbNO₃ →
PbI₂ + KNO₃
Answer: (b)
4. A metal
ribbon 'X' burns in oxygen with a dazzling white flame forming a white ash 'Y'.
The correct description is:
[CBSE 2023]
(a) X = Ca; Y = CaO; Type = Decomposition
(b) X = Mg; Y = MgO; Type = Combination
(c) X = Al; Y = Al₂O₃; Type = Thermal decomposition
(d) X = Zn; Y = ZnO; Type = Endothermic
Answer: (b)
5. The
balanced equation showing reaction between quick lime and water is: [CBSE 2023]
(a) 2CaO + H₂O →
2CaOH + H₂ + Heat
(b) CaO + H₂O →
Ca(OH)₂ + H₂ + Heat
(c) CaO + H₂O →
Ca(OH)₂ + Heat
(d) 2CaO + 3H₂O →
2Ca(OH)₃ + O₂ + Heat
Answer: (c)
6. In the
reaction: 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)↑, the reducing agent is: [CBSE 2023]
(a) Na
(b) H₂O
(c) NaOH
(d) H₂
Answer: (a)
7. A
student took sodium sulphate solution and added barium chloride solution. The
colour and formula of the insoluble substance formed is: [CBSE 2021-22]
(a) grey, Ba₂SO₄
(b) yellow, Ba(SO₄)₂
(c) white, BaSO₄
(d) pink, BaSO₄
Answer: (c)
8. C₆H₁₂O₆(aq) + 6O₂(g) → 6CO₂(g) + 6H₂O(l). The above reaction is a/an: [CBSE 2021-22]
(a) displacement reaction
(b) endothermic reaction
(c) exothermic reaction
(d) neutralisation reaction
Answer: (c)
9. Which
statement about the reaction MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂ is correct? [CBSE 2021-22]
(i) HCl is oxidized to Cl₂
(ii) MnO₂ is
reduced to MnCl₂
(iii) MnCl₂ acts as
an oxidizing agent
(iv) HCl acts as an oxidizing agent
(a) (ii), (iii) and (iv)
(b) (i), (ii) and (iii)
(c) (i) and (ii) only
(d) (iii) and (iv) only
Answer: (c)
10. Which
one is categorised as thermal decomposition reaction? [CBSE 2021-22]
(a) 2H₂O(l) →
2H₂(g) + O₂(g)
(b) 2AgBr(s) → 2Ag(s) + Br₂(g)
(c) 2AgCl(s) → 2Ag(s) + Cl₂(g)
(d) CaCO₃(s) →
CaO(s) + CO₂(g)
Answer: (d)
11. When
hydrogen sulphide gas is passed through blue copper sulphate solution, a black
precipitate of copper sulphide is obtained. This is an example of: [CBSE 2020]
(a) combination reaction
(b) displacement reaction
(c) decomposition reaction
(d) double displacement reaction
Answer: (d)
12. Copper
utensils slowly lose their shiny brown surface and gain a green coat. This is
due to formation of:
[CBSE 2020]
(a) copper sulphate
(b) copper carbonate
(c) cupric oxide
(d) cuprous oxide
Answer: (b)
Read the full blog here: The Age of Revolutions: 1830–1848 – Class 10 Notes.
Short Answer Questions- CBSE Board PYQs
Q1.
Name the type of chemical reaction which takes place when quicklime is added to
water. [CBSE 2021]
Answer: Combination reaction and exothermic reaction.
CaO(s) + H₂O(l) →
Ca(OH)₂(aq) +
Heat
Q2. Give the chemical
name of the reactants as well as the products of the following equation: [CBSE 2021]
HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O
Answer:
Reactants: Nitric acid (HNO₃)
and Calcium hydroxide [Ca(OH)₂]
Products: Calcium nitrate [Ca(NO₃)₂] and Water (H₂O)
Q3. Why should a
magnesium ribbon be cleaned before burning in air? [CBSE Board]
Answer: Magnesium ribbon should be cleaned to remove the layer
of magnesium oxide from its surface so that it burns properly in air.
Q4. Write one equation
each for decomposition reactions where energy is supplied in the form of heat,
light, and electricity. [CBSE 2018]
Answer:
· Heat: CaCO₃ → CaO + CO₂
· Light: 2AgCl → 2Ag + Cl₂
· Electricity: 2H₂O → 2H₂ + O₂
Q5. Name the type of
chemical reactions represented by:
[CBSE 2016]
(i) CaCO₃ → CaO + CO₂
(ii) CaO + H₂O → Ca(OH)₂
(iii) Zn + H₂SO₄ → ZnSO₄ + H₂
Answer:
(i) Decomposition reaction
(ii) Combination reaction
(iii) Displacement reaction
Q6. Why is respiration
considered an exothermic reaction?
[CBSE Board]
Answer:
Respiration releases energy in the form of heat when glucose combines with
oxygen in our body cells, making it an exothermic process.
C₆H₁₂O₆(aq)
+ 6O₂(g) →
6CO₂(g) + 6H₂O(l) + Energy.
Read: The Making of Nationalism in Europe – Class 10 Notes
Long Answer Questions- CBSE Board PYQs
Q1. What is a balanced chemical
equation? Why should chemical equations be balanced? Write the chemical
equation where change in colour occurs. [CBSE 2017]
Answer:
A balanced chemical equation has equal numbers of atoms of each element on both
the reactant and product sides. Chemical equations should be balanced because
according to the Law of
Conservation of Mass, matter cannot be created or destroyed in
a chemical reaction. The total mass of reactants must equal the total mass of
products.
Example of change in colour:
Fe + CuSO₄ →
FeSO₄ + Cu
(Blue solution becomes green, brown copper is deposited)
Q2. Classify the following reactions into different types: [CBSE 2019]
(i) AgNO₃(aq) +
NaCl(aq) → AgCl(s) + NaNO₃(aq)
(ii) CaO(s) + H₂O(l) →
Ca(OH)₂(aq)
(iii) 2KClO₃(s) →
2KCl(aq) + 3O₂(g)
(iv) Zn + CuSO₄ →
ZnSO₄ + Cu
Answer:
(i) Double displacement / Precipitation reaction
(ii) Combination reaction
(iii) Decomposition reaction
(iv) Displacement reaction
Q3. A student mixes sodium sulphate
powder in barium chloride powder. What change would the student observe?
Justify your answer and explain how he can obtain the desired change. [CBSE 2019]
Answer: When student mixes Na₂SO₄ powder with BaCl₂ powder, no change will be observed.
The student needs to prepare aqueous
solutions of Na₂SO₄ and BaCl₂ separately in two different test
tubes. When these two solutions are mixed, a double displacement
(precipitation) reaction takes place:
Na₂SO₄(aq) + BaCl₂(aq) →
BaSO₄(s)↓
+ 2NaCl(aq)
(White precipitate)
Q4.
2g of ferrous sulphate crystals are heated in a dry boiling tube. [CBSE 2019]
(a) List any two
observations
(b) Name the type of
chemical reaction
(c) Write balanced
chemical equation
Answer:
(a) Observations:
· Ferrous sulphate crystals lose water when heated and the colour changes
· Brown fumes of gases (SO₂ and SO₃) with smell of burning sulphur are evolved
· Yellow-brown residue of Fe₂O₃ is left behind
(b) Thermal decomposition reaction
(c) 2FeSO₄·7H₂O → Fe₂O₃ + SO₂ + SO₃ + 14H₂O
Q5. You might have noted that when
copper powder is heated in a China dish, the reddish brown surface becomes
coated with a black substance.
[CBSE 2019]
(a) Why has this black
substance formed?
(b) What is the black
substance?
(c) Write the chemical
equation
(d) How can the black
coating be turned reddish brown?
Answer:
(a) The
black substance is formed because copper combines with oxygen in air (oxidation
of copper takes place)
(b) The black substance is copper oxide (CuO)
(c) 2Cu + O₂ → 2CuO
(d) The black coating can be turned
reddish brown by passing
hydrogen gas over the hot copper oxide:
CuO(s) + H₂(g) →
Cu(s) + H₂O
(Reddish brown)
Q6.
In the electrolysis of water:
[CBSE 2020]
(a) Name the gases
liberated at anode and cathode
(b) Why is the volume of
gas collected on one electrode double that on the other?
(c) What would happen if
dil. H₂SO₄ is not added to water?
Answer:
(a) At
cathode: Hydrogen (H₂), At anode: Oxygen (O₂)
(b) The volume of hydrogen is double that
of oxygen because from the balanced equation:
2H₂O →
2H₂ + O₂
The ratio H₂:O₂ = 2:1
(c) Pure water does not conduct electricity. A few drops of dil. H₂SO₄ are added to make water conducting.
Q7.
What is rancidity? Mention any two ways by which rancidity can be prevented. [CBSE 2012]
Answer: The process in which taste and smell of food containing
fats and oils gets spoiled due to oxidation is called rancidity.
Prevention from rancidity:
· Antioxidants are added to fatty foods to prevent oxidation
· Food should be kept in airtight containers in refrigerator
· Chips packets are flushed with nitrogen gas which prevents oxidation
Q8.
Define double displacement reaction. Write the chemical equation of a double displacement
reaction which is also (i) Neutralisation reaction and (ii) Precipitation
reaction. [CBSE
2023]
Answer: A chemical reaction in which two reactants exchange
ions to form two new compounds is called a double displacement reaction.
(i)
Neutralisation reaction:
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
(Base + Acid → Salt + Water)
(ii)
Precipitation reaction:
Pb(NO₃)₂(aq) + 2KI(aq) →
PbI₂(s)↓
+ 2KNO₃(aq)
(Yellow precipitate of PbI₂
forms)
Q9.
What is a reduction reaction? Identify the substances that are oxidised and
reduced in:
[CBSE 2015]
(a) Fe₂O₃ + 2Al → Al₂O₃ + 2Fe
(b) 2PbO + C → 2Pb + CO₂
Answer: Reduction is a reaction in which oxygen is removed or hydrogen is added or gain of electrons takes place.
(a) Fe₂O₃ + 2Al → Al₂O₃ + 2Fe
· Fe₂O₃ is reduced to Fe (oxygen removed)
· Al is oxidised to Al₂O₃ (oxygen added)
(b) 2PbO + C → 2Pb + CO₂
· PbO is reduced to Pb (oxygen removed)
· C is oxidised to CO₂ (oxygen added)
Q10.
Lead nitrate solution is added to a test tube containing potassium iodide
solution. [CBSE
2020]
(a) Write the name and
colour of the compound precipitated
(b) Write the balanced
chemical equation
(c) Name the type of
reaction
Answer:
(a)
Compound: Lead iodide
(PbI₂), Colour: Yellow
(b) Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s)↓ + 2KNO₃(aq)
(c) Double displacement reaction / Precipitation reaction.
Download Class 10 Science Notes PDF
Looking for class 10 science notes PDF download or class 10 chemical reactions and equations notes PDF? This complete guide covers all topics from Chapter 1 with NCERT-based explanations, making it perfect for your CBSE Board 2026 preparation.
Key Features of These Notes:
· ✅ Easy language explanations
· ✅ Complete NCERT syllabus coverage
· ✅ MCQs with answers
· ✅ Short and long questions
· ✅ Exam-focused content
· ✅ Balancing equations methods
· ✅ All types of reactions explained
Download PDF: Click Here.
Conclusion
Chemical Reactions and Equations is one of the most scoring chapters in Class 10 Science because CBSE repeatedly asks questions on balancing equations, types of reactions, and redox/corrosion concepts in the board paper pattern. It’s not enough to just read the theory—real improvement comes when you revise short notes and practice PYQs, because that is where students learn the exact language and format CBSE expects in answers. If you revise this chapter 2–3 times and practice the important MCQs + short and long questions, you can easily convert it into confident marks in Board Exam 2026.
Now
use this chapter as your “base chapter” of chemistry: once balancing and
reaction identification becomes easy, upcoming chapters like Acids, Bases and
Salts and Metals and Non-metals also feel simpler. Keep your revision strategy simple:
learn the definitions, practice 8–10 balanced equations daily, and solve PYQs
in timed mode to build speed and accuracy.
You now have complete NCERT-based notes on “Chemical Reactions & Equations" in very simple English!
For more NCERT-based Class 10
Science notes, exam tips, and study materials, bookmark this page and share
with your friends. If you have doubts about any concept, comment below. All the
best for your board exams!
📘 CBSE Class 10 Board Exam 2025: 30-Day Daily Study & Revision Planner
Not just a timetable —
This is a COMPLETE DAILY STUDY SYSTEM used by smart toppers.
📕 This Planner Includes:
✅ 30 Days’ Time Table
✅ Daily Study Planner Pages (30 Days)
✅ Slot-wise Study Planning
✅ Concept / Notes / Revision / MCQ Slots
✅ End-of-Day Performance Checker
✅ Error Log & Mistake Tracking
✅ Wellness & Focus Tracker
✅ 30-Day Subject-Wise Revision Table
📄 Daily Study Planner Page:
Each day includes:
• Target study hours
• Top 6 priorities
• 4 Study Slots:
- Concepts / Notes
- Revision / Diagram / Map
- MCQs / Case-Based / PYQs
• Status Tracker (Done / Half / Not Done)
• Error Log (Mistakes Analysis)
• End-of-Day Performance Review
• Wellness Check (Sleep, Stress, Breaks)
Who Should Buy This?
✔️ CBSE Class 10 Students
✔️ Students scared of board exams
✔️ Students who waste time planning daily
✔️ Students aiming 75% – 95%
✔️ Parents who want a structured plan for kids.
🔗 **[Get Your Copy Now]**
**Special Offer:** Early bird students get 50% OFF! ⏰
No comments:
Post a Comment