Introduction

Chemistry is all around us. Every day, countless chemical reactions occur in nature and in our daily lives. From cooking food and digesting meals to rusting of iron and burning of fuel, chemical reactions are responsible for many changes that make life possible. (Chemical Reactions and Equations Class 10 Notes)

Understanding chemical reactions helps us explain how substances change into new substances with different properties. This chapter introduces the concept of chemical reactions, chemical equations, balanced equations, and the different types of reactions that form the foundation of chemistry.

Whether you are preparing for school exams or the CBSE Board Examination, mastering this chapter is essential because it forms the basis for many advanced chemistry topics.

What is a Chemical Reaction?

A chemical reaction is a process in which one or more substances change into one or more new substances having different chemical properties.

The substances present before the reaction are called reactants, while the new substances formed are called products.

Definition

A chemical reaction is a process in which reactants are converted into products with different physical and chemical properties.

Everyday Examples of Chemical Reactions

Chemical reactions occur continuously around us. Some common examples include:

These examples show that chemical reactions are an essential part of our daily lives.

What Happens During a Chemical Reaction?

During a chemical reaction:

• Old chemical bonds break.
• New chemical bonds are formed.
• Atoms rearrange themselves.
• New substances with different properties are produced.
• Energy may be absorbed or released.

For example,

Hydrogen + Oxygen → Water

Hydrogen is a highly flammable gas, while oxygen supports combustion. However, when they react chemically, they form water, a liquid with entirely different properties.

This demonstrates that the products of a chemical reaction have properties that are different from those of the reactants.

Reactants and Products

Every chemical reaction has two important components:

Reactants

Reactants are the substances that take part in a chemical reaction.

Example:

Hydrogen + Oxygen

Here, hydrogen and oxygen are reactants.

Products

Products are the new substances formed after the reaction.

Example:

Water

Here, water is the product.

Example

Hydrogen + Oxygen → Water

• Reactants: Hydrogen, Oxygen
• Product: Water

Characteristics of a Chemical Reaction

Several observable changes indicate that a chemical reaction has taken place.

1. Evolution of Gas

Many reactions produce gases.

Example

When zinc reacts with dilute hydrochloric acid, hydrogen gas is produced.

Equation:

Zn + 2HCl → ZnCl₂ + H₂↑

Observation

• Bubbles appear.
• Hydrogen gas is released.

2. Change in Colour

Sometimes, the colour of substances changes during a reaction.

Example

Iron reacts with copper sulphate solution.

Fe + CuSO₄ → FeSO₄ + Cu

Observation

• Blue solution becomes green.
• Brown copper metal is deposited.

3. Formation of a Precipitate

A precipitate is an insoluble solid formed during a chemical reaction.

Example

AgNO₃ + NaCl → AgCl↓ + NaNO₃

Observation

A white precipitate of silver chloride is formed.

4. Change in Temperature

Some reactions release heat, while others absorb heat.

Exothermic Reaction

A reaction that releases heat.

Example:

Burning of natural gas.

Endothermic Reaction

A reaction that absorbs heat.

Example:

Photosynthesis.

5. Change in State

Sometimes, substances change from one physical state to another.

Example

Hydrogen gas reacts with oxygen gas to form liquid water.

This shows a change from gases to liquid.

Physical Change vs Chemical Change

Students often confuse physical changes with chemical changes.

The following table highlights the key differences:

How to Identify a Chemical Reaction?

Ask yourself these questions:

✔ Has a new substance been formed?

✔ Has gas evolved?

✔ Has heat been released or absorbed?

✔ Has the colour changed?

✔ Has a precipitate formed?

✔ Has the smell changed?

If the answer to one or more of these is Yes, a chemical reaction has likely occurred.

Did You Know?

🔥 Your body performs thousands of chemical reactions every second to keep you alive. Digestion, respiration, muscle movement, and even thinking involve chemical reactions.

Exam Tip

Remember: A chemical reaction always results in the formation of one or more new substances with different properties. Simply changing the shape or state of a substance (such as melting ice) is not a chemical reaction.

Quick Revision

• A chemical reaction converts reactants into products.
• Products have properties different from reactants.
• Chemical reactions involve breaking and forming chemical bonds.
• Common signs of a chemical reaction include:
  • Evolution of gas
  • Change in colour
  • Formation of a precipitate
  • Temperature change
  • Change in state
• Physical changes do not form new substances, whereas chemical changes do.

Chemical Equations

Writing a complete sentence to describe a chemical reaction is often lengthy and inconvenient. Chemists therefore use chemical equations, which provide a short and precise way to represent a chemical reaction using chemical symbols and formulae.

A chemical equation tells us:

• Which substances are reacting (reactants)
• Which substances are formed (products)
• The physical states of substances
• The conditions required for the reaction (if any)
• Whether heat, light, electricity, or a catalyst is involved

Thus, a chemical equation is the universal language of chemistry.

Definition

A chemical equation is the symbolic representation of a chemical reaction using the chemical symbols and formulae of the reactants and products.

Why Do We Need Chemical Equations?

Chemical equations are useful because they:

• Save time and space.
• Represent reactions in a standard format.
• Are understood by scientists worldwide.
• Help calculate the quantities of reactants and products.
• Show the exact composition of substances involved in a reaction.

Types of Chemical Equations

There are three common ways to represent a chemical reaction.

1. Word Equation

A word equation uses the names of the reactants and products.

Example

Magnesium + Oxygen → Magnesium Oxide

Although easy to understand, word equations do not provide detailed information such as the chemical formula or the number of atoms.

2. Skeletal Chemical Equation

A skeletal equation uses chemical symbols and formulae but may not have equal numbers of atoms on both sides.

Example

Mg + O₂ → MgO

This equation is not balanced because:

Since oxygen atoms are unequal, this equation does not satisfy the Law of Conservation of Mass.

3. Balanced Chemical Equation

A balanced chemical equation has the same number of atoms of each element on both sides of the equation.

Example

2Mg + O₂ → 2MgO

Now,

The equation is balanced because the number of atoms is equal on both sides.

Parts of a Chemical Equation

Consider the equation:

Zn + 2HCl → ZnCl₂ + H₂

It contains several important components.

Reactants

Substances present before the reaction.

• Zinc (Zn)
• Hydrochloric acid (HCl)

Products

Substances formed after the reaction.

• Zinc chloride (ZnCl₂)
• Hydrogen gas (H₂)

Arrow (→)

The arrow means “yields” or “produces.”

Plus Sign (+)

It separates different reactants or products.

Physical State Symbols

Chemical equations often include symbols showing the physical state of each substance.

Example

CaCO₃(s) → CaO(s) + CO₂(g)

This equation tells us that:

• Calcium carbonate is a solid.
• Calcium oxide is a solid.
• Carbon dioxide is a gas.

Special Symbols Used in Chemical Equations

Example

Heating calcium carbonate:

CaCO₃(s) ─Δ→ CaO(s) + CO₂(g)

The symbol Δ indicates that heat is supplied.

Law of Conservation of Mass

Before learning how to balance equations, we must understand an important scientific law.

Statement

Mass can neither be created nor destroyed during a chemical reaction.

This means:

Total mass of reactants = Total mass of products

Since atoms are neither created nor destroyed, every chemical equation must contain equal numbers of atoms of each element on both sides.

Why Should Chemical Equations Be Balanced?

Balanced equations ensure that:

• The Law of Conservation of Mass is satisfied.
• The number of atoms remains the same before and after the reaction.
• The equation correctly represents the actual chemical reaction.
• Stoichiometric calculations can be performed accurately.

How to Balance a Chemical Equation

Balancing a chemical equation means making the number of atoms of each element equal on both sides without changing the chemical formulae.

Important Rule: Never change the chemical formula of a compound. Only change the coefficients placed before the formulae.

Step-by-Step Method for Balancing Chemical Equations (Chemical Reactions and Equations Class 10 Notes)

Consider the skeletal equation:

Fe + O₂ → Fe₂O₃

Step 1: Count the atoms

Clearly, the equation is unbalanced.

Step 2: Balance the metal atoms first

Multiply iron on the left by 4.

4Fe + O₂ → 2Fe₂O₃

Now,

Step 3: Balance oxygen

Multiply oxygen by 3.

4Fe + 3O₂ → 2Fe₂O₃

Now,

The equation is now balanced.

Another Solved Example

Balance:

H₂ + O₂ → H₂O

Step 1

Count atoms.

Oxygen is not balanced.

Step 2

Multiply water by 2.

H₂ + O₂ → 2H₂O

Now,

Hydrogen becomes unequal.

Step 3

Multiply hydrogen by 2.

2H₂ + O₂ → 2H₂O

Final count:

Balanced equation obtained.

Important Rules While Balancing

✔ Never change the chemical formula.

✔ Change only the coefficients.

✔ Balance metals first.

✔ Balance non-metals next.

✔ Balance hydrogen and oxygen last whenever possible.

✔ Check every atom before writing the final answer.

Examples of Balanced Chemical Equations

Exam Tip

In the CBSE Board Examination, balancing chemical equations is one of the most frequently asked questions. Practice balancing different equations regularly and always verify the number of atoms before writing the final answer.

Did You Know?

The balanced chemical equation not only shows the substances involved but also indicates the ratio in which they react. For example:

2H₂ + O₂ → 2H₂O

This means:

• 2 molecules of hydrogen react with
• 1 molecule of oxygen to produce
• 2 molecules of water.

Quick Revision

• A chemical equation represents a reaction using symbols and formulae.
• A word equation uses names of substances.
• A skeletal equation is usually unbalanced.
• A balanced equation has equal numbers of atoms of each element on both sides.
• The Law of Conservation of Mass states that mass is neither created nor destroyed during a chemical reaction.
• Never change the chemical formula while balancing an equation; only adjust the coefficients.
• State symbols (s), (l), (g), (aq) indicate the physical state of substances.
• Symbols like Δ, ↑, and ↓ provide additional information about the reaction.

Types of Chemical Reactions

Chemical reactions can be classified into different categories based on how reactants are converted into products. Understanding these types helps us predict reaction products and explain many natural and industrial processes.

The five major types of chemical reactions covered in the CBSE Class 10 syllabus are:

1. Combination Reaction
2. Decomposition Reaction
3. Displacement Reaction
4. Double Displacement Reaction
5. Oxidation–Reduction (Redox) Reaction

Each type has unique characteristics and applications in everyday life.

1. Combination Reaction

Definition

A combination reaction is a chemical reaction in which two or more reactants combine to form a single product.

General Equation

A + B → AB

In this type of reaction, the number of products is always one.

Example 1: Formation of Water

$$2H_2 + O_2 \rightarrow 2H_2O$$2H2​+O2​→2H2​O

Hydrogen gas combines with oxygen gas to produce water.

Example 2: Burning of Magnesium Ribbon

$$2Mg + O_2 \rightarrow 2MgO$$2Mg+O2​→2MgO

When a magnesium ribbon is ignited, it burns with a dazzling white flame and forms a white powder called magnesium oxide.

Observation

• Bright white flame
• White ash is formed
• Heat and light are released

Example 3: Formation of Quick Lime

$$CaO + H_2O \rightarrow Ca(OH)_2 + \text{Heat}$$CaO+H2​O→Ca(OH)2​+Heat

Calcium oxide reacts with water to form calcium hydroxide.

This reaction releases a large amount of heat and is therefore exothermic.

Characteristics of Combination Reactions

• Two or more reactants combine.
• Only one product is formed.
• Many combination reactions release heat.
• Common in nature and industries.

Everyday Examples

• Burning of coal
• Formation of water
• Formation of rust (simplified)
• Photosynthesis (overall reaction)

Memory Tip

Many → One

Many reactants combine to produce one product.

Exothermic Combination Reactions

Most combination reactions release energy.

Such reactions are called exothermic reactions.

Definition

An exothermic reaction is a reaction in which heat is released to the surroundings.

Examples

• Burning LPG
• Burning petrol
• Respiration
• Burning magnesium ribbon

Endothermic Reactions

Some reactions absorb heat from the surroundings.

These are called endothermic reactions.

Definition

An endothermic reaction absorbs heat during the reaction.

Example

Photosynthesis$$6CO_2 + 6H_2O \xrightarrow{\text{Sunlight}} C_6H_{12}O_6 + 6O_2$$6CO2​+6H2​OSunlight​C6​H12​O6​+6O2​

Plants absorb sunlight to prepare food.

2. Decomposition Reaction

Definition

A decomposition reaction is a reaction in which one compound breaks down into two or more simpler substances.

General Equation

AB → A + B

This is the opposite of a combination reaction.

Types of Decomposition Reactions

There are three main types:

1. Thermal Decomposition
2. Electrolytic Decomposition
3. Photolytic Decomposition

A. Thermal Decomposition

When heat causes a compound to decompose, the reaction is called thermal decomposition.

Example

$$CaCO_3 \xrightarrow{\Delta} CaO + CO_2$$CaCO3​Δ​CaO+CO2​

Calcium carbonate decomposes into calcium oxide and carbon dioxide.

Uses

• Manufacture of cement
• Production of quick lime

Example

$$2Pb(NO_3)_2 \xrightarrow{\Delta} 2PbO + 4NO_2 + O_2$$2Pb(NO3​)2​Δ​2PbO+4NO2​+O2​

Observation

• Brown nitrogen dioxide gas evolves.
• Oxygen gas is released.
• Yellow lead oxide remains.

B. Electrolytic Decomposition

In this reaction, electricity breaks down a compound.

Example

$$2H_2O \xrightarrow{\text{Electricity}} 2H_2 + O_2$$2H2​OElectricity​2H2​+O2​

Water decomposes into hydrogen and oxygen gases.

C. Photolytic Decomposition

Sunlight causes decomposition.

Example

$$2AgCl \xrightarrow{\text{Sunlight}} 2Ag + Cl_2$$2AgClSunlight​2Ag+Cl2​

Silver chloride changes from white to grey because metallic silver is formed.

Another example:$$2AgBr \xrightarrow{\text{Sunlight}} 2Ag + Br_2$$2AgBrSunlight​2Ag+Br2​

This reaction is used in black-and-white photography.

Characteristics of Decomposition Reactions

• One reactant
• Two or more products
• Heat, light, or electricity is needed
• Usually endothermic

Everyday Applications

• Manufacture of cement
• Electrolysis of water
• Photography
• Extraction of metals

Combination vs Decomposition

3. Displacement Reaction

Definition

A displacement reaction is a reaction in which a more reactive element displaces a less reactive element from its compound.

General Equation

A + BC → AC + B

Here,

A is more reactive than B.

Example 1

$$Zn + CuSO_4 \rightarrow ZnSO_4 + Cu$$Zn+CuSO4​→ZnSO4​+Cu

Observation

• Blue copper sulphate solution becomes colourless or pale.
• Copper metal is deposited.

Example 2

$$Fe + CuSO_4 \rightarrow FeSO_4 + Cu$$Fe+CuSO4​→FeSO4​+Cu

Observation

• Blue solution changes to green.
• Copper deposits on the iron nail.

Why Does This Happen?

Because:

Zinc > Iron > Copper

in the reactivity series.

A more reactive metal replaces a less reactive metal.

Everyday Applications

• Metal extraction
• Electroplating
• Rust prevention
• Industrial metal production

4. Double Displacement Reaction

Definition

A double displacement reaction is one in which two compounds exchange their ions to form two new compounds.

General Equation

AB + CD → AD + CB

Example

$$AgNO_3 + NaCl \rightarrow AgCl + NaNO_3$$AgNO3​+NaCl→AgCl+NaNO3​

A white precipitate of silver chloride is formed.

Another Example

$$BaCl_2 + Na_2SO_4 \rightarrow BaSO_4 + 2NaCl$$BaCl2​+Na2​SO4​→BaSO4​+2NaCl

A white precipitate of barium sulphate forms.

Precipitation Reaction

A precipitation reaction is a type of double displacement reaction in which an insoluble solid (precipitate) is produced.

Examples:

• Silver chloride
• Barium sulphate

Neutralisation Reaction

A neutralisation reaction is also a double displacement reaction.

Example

$$HCl + NaOH \rightarrow NaCl + H_2O$$HCl+NaOH→NaCl+H2​O

Acid + Base → Salt + Water

Characteristics

• Ion exchange occurs.
• New compounds are formed.
• Often produces precipitates.
• Neutralisation is a common example.

Difference Between Displacement and Double Displacement

Quick Comparison of Four Reaction Types

Exam Tip

Remember the reaction patterns rather than memorising every equation. If you recognise the pattern (combination, decomposition, displacement, or double displacement), identifying the reaction type in the exam becomes much easier.

Did You Know?

Thermite Reaction is a highly exothermic displacement reaction:$$Fe_2O_3 + 2Al \rightarrow Al_2O_3 + 2Fe + \text{Heat}$$The intense heat produced is used for welding railway tracks and repairing heavy machinery.

Oxidation and Reduction (Redox Reactions)

Many chemical reactions involve the transfer of oxygen or hydrogen between substances. These reactions are called oxidation and reduction reactions. When oxidation and reduction occur simultaneously in the same reaction, the reaction is known as a redox reaction.

Understanding redox reactions is important because they occur in respiration, photosynthesis, combustion, corrosion, batteries, and many industrial processes.

Oxidation

Definition

Oxidation is the process in which:

• Oxygen is added to a substance, or
• Hydrogen is removed from a substance.

Example 1

$$2Cu + O_2 \rightarrow 2CuO$$2Cu+O2​→2CuO

Copper reacts with oxygen to form black copper(II) oxide.

Observation:

• Reddish-brown copper turns black.
• Oxygen is added to copper.

Therefore, copper undergoes oxidation.

Example 2

$$C + O_2 \rightarrow CO_2$$C+O2​→CO2​

Carbon combines with oxygen to form carbon dioxide.

Carbon is oxidised.

Reduction

Definition

Reduction is the process in which:

• Oxygen is removed from a substance, or
• Hydrogen is added to a substance.

Example

$$CuO + H_2 \rightarrow Cu + H_2O$$CuO+H2​→Cu+H2​O

Hydrogen removes oxygen from copper oxide, producing copper and water.

Observation:

• Black copper oxide changes into reddish-brown copper.
• Oxygen is removed from CuO.

Therefore, copper oxide undergoes reduction.

Redox Reaction

Definition

A redox reaction is a chemical reaction in which oxidation and reduction take place simultaneously.

Example

$$CuO + H_2 \rightarrow Cu + H_2O$$CuO+H2​→Cu+H2​O

Here:

• Copper oxide loses oxygen → Reduction
• Hydrogen gains oxygen → Oxidation

Both processes occur together, making it a redox reaction.

Oxidising Agent

Definition

An oxidising agent is a substance that causes oxidation of another substance by supplying oxygen or removing hydrogen.

The oxidising agent itself gets reduced during the reaction.

Example

In the reaction:$$CuO + H_2 \rightarrow Cu + H_2O$$CuO+H2​→Cu+H2​O

Copper oxide supplies oxygen to hydrogen.

Therefore:

• Copper oxide (CuO) is the oxidising agent.

Reducing Agent

Definition

A reducing agent is a substance that causes reduction by removing oxygen or supplying hydrogen.

The reducing agent itself gets oxidised during the reaction.

Example

Again,$$CuO + H_2 \rightarrow Cu + H_2O$$CuO+H2​→Cu+H2​O

Hydrogen removes oxygen from copper oxide.

Therefore:

• Hydrogen (H₂) is the reducing agent.

Difference Between Oxidation and Reduction

Everyday Examples of Oxidation

• Burning of wood
• Burning LPG
• Rusting of iron
• Digestion of food
• Respiration
• Combustion of petrol
• Browning of cut fruits

Everyday Examples of Reduction

• Extraction of metals from ores
• Hydrogenation of vegetable oils
• Reduction of copper oxide
• Manufacture of metals in industries

Corrosion

Definition

Corrosion is the slow destruction of metals due to chemical reactions with air, moisture, acids, or other substances present in the environment.

Corrosion damages metals and reduces their strength and usefulness.

Rusting of Iron

Rusting is the most common example of corrosion.

When iron is exposed to oxygen and moisture, it forms a reddish-brown substance called rust.

Chemical Equation

$$4Fe + 3O_2 + xH_2O \rightarrow 2Fe_2O_3 \cdot xH_2O$$4Fe+3O2​+xH2​O→2Fe2​O3​⋅xH2​O

Rust is hydrated iron(III) oxide.

Conditions Necessary for Rusting

Two conditions are essential:

• Oxygen
• Water (moisture)

If either oxygen or moisture is absent, rusting does not occur.

Characteristics of Rust

• Reddish-brown colour
• Flaky and porous
• Weakens iron
• Spreads gradually over the metal surface

Harmful Effects of Corrosion

Corrosion can lead to:

• Damage to bridges
• Weakening of buildings
• Leakage in pipelines
• Damage to vehicles
• Failure of machinery
• High maintenance costs
• Loss of valuable metals

Prevention of Corrosion

Several methods are used to protect metals from corrosion.

1. Painting

A layer of paint prevents air and moisture from reaching the metal surface.

Examples:

• Gates
• Window grills
• Iron railings

2. Oiling and Greasing

Oil or grease forms a protective coating.

Examples:

• Bicycle chains
• Machine parts
• Industrial equipment

3. Galvanisation

Galvanisation is the process of coating iron with a thin layer of zinc.

Zinc protects iron from rusting even if the surface is scratched.

Uses:

• Water pipes
• Buckets
• Roofing sheets
• Iron poles

4. Electroplating

A thin layer of another metal is deposited on the surface.

Examples:

• Chromium plating
• Silver plating
• Gold plating

Electroplating improves both appearance and corrosion resistance.

5. Alloying

An alloy is a mixture of two or more elements, at least one of which is a metal.

Alloys are generally stronger and more resistant to corrosion.

Example

Stainless Steel

Contains:

• Iron
• Chromium
• Nickel
• Carbon

Stainless steel does not rust easily.

Rancidity

Definition

Rancidity is the spoilage of oils and fats due to oxidation, resulting in an unpleasant smell and taste.

Foods containing fats and oils become rancid when exposed to air for a long time.

Causes of Rancidity

• Oxygen in air
• Heat
• Sunlight
• Moisture
• Long storage

Examples of Rancidity

• Chips
• Butter
• Ghee
• Fried snacks
• Nuts
• Biscuits

Prevention of Rancidity

1. Airtight Containers

Reduce contact with oxygen.

2. Refrigeration

Low temperature slows oxidation.

3. Vacuum Packing

Air is removed from food packets.

4. Nitrogen Flushing

Packets of chips are filled with nitrogen gas.

Nitrogen is less reactive and prevents oxidation.

5. Use of Antioxidants

Antioxidants such as BHA (Butylated Hydroxyanisole) and BHT (Butylated Hydroxytoluene) are added to increase shelf life.

Everyday Applications

Activity: Observe Rusting

Materials

• Two iron nails
• Water
• Two test tubes

Procedure

1. Place one nail in dry air.
2. Place another nail in water.
3. Leave both for a few days.

Observation

The nail exposed to water and air develops rust, while the nail kept dry remains unchanged.

Conclusion

Both oxygen and moisture are necessary for rusting.

Exam Tip

Remember: Oxidation and reduction always occur together in a redox reaction. If one substance is oxidised, another must be reduced.

Did You Know?

The Statue of Liberty appears green because copper on its surface has undergone corrosion, forming a protective green layer called patina. Unlike rust on iron, this layer protects the copper underneath from further corrosion.

Important Definitions

1. Chemical Reaction

A process in which one or more substances (reactants) are converted into new substances (products) with different chemical properties.

2. Reactants

The substances that take part in a chemical reaction.

3. Products

The new substances formed after a chemical reaction.

4. Chemical Equation

A symbolic representation of a chemical reaction using chemical symbols and formulae.

5. Balanced Chemical Equation

A chemical equation in which the number of atoms of each element is the same on both sides of the equation.

6. Combination Reaction

A reaction in which two or more substances combine to form a single product.

7. Decomposition Reaction

A reaction in which one compound breaks down into two or more simpler substances.

8. Displacement Reaction

A reaction in which a more reactive element displaces a less reactive element from its compound.

9. Double Displacement Reaction

A reaction in which two compounds exchange their ions to form two new compounds.

10. Oxidation

The addition of oxygen or removal of hydrogen from a substance.

11. Reduction

The removal of oxygen or addition of hydrogen to a substance.

12. Redox Reaction

A chemical reaction in which oxidation and reduction occur simultaneously.

13. Corrosion

The gradual destruction of metals due to reaction with air, moisture, or chemicals.

14. Rusting

A type of corrosion in which iron reacts with oxygen and moisture to form hydrated iron(III) oxide (rust).

15. Rancidity

The oxidation of fats and oils, causing food to develop an unpleasant smell and taste.

NCERT Keywords

• Chemical Reaction
• Reactants
• Products
• Chemical Equation
• Balanced Equation
• Combination Reaction
• Decomposition Reaction
• Thermal Decomposition
• Electrolytic Decomposition
• Photolytic Decomposition
• Displacement Reaction
• Double Displacement Reaction
• Precipitation Reaction
• Neutralisation Reaction
• Oxidation
• Reduction
• Redox Reaction
• Oxidising Agent
• Reducing Agent
• Corrosion
• Rusting
• Galvanisation
• Electroplating
• Alloy
• Rancidity
• Antioxidant

Important Chemical Equations to Remember

Commonly Confused Concepts

Real-Life Applications

Understanding chemical reactions helps us explain many everyday phenomena:

• Cooking food
• Digestion
• Respiration
• Photosynthesis
• Burning of fuels
• Rusting of iron
• Manufacturing cement
• Electroplating jewellery
• Food preservation
• Extraction of metals

Chemistry is not limited to laboratories—it is part of daily life.

One-Page Quick Revision

Remember These Points

• Chemical reactions form new substances.
• Chemical equations represent reactions symbolically.
• Balanced equations obey the Law of Conservation of Mass.
• Combination reactions produce one product.
• Decomposition reactions split one compound into simpler substances.
• Displacement reactions occur according to the reactivity series.
• Double displacement reactions involve exchange of ions.
• Oxidation means addition of oxygen.
• Reduction means removal of oxygen.
• Corrosion damages metals.
• Galvanisation prevents rusting.
• Rancidity spoils food containing fats and oils.

Board Exam Tips

✔ Learn all important chemical equations.

✔ Practice balancing equations daily.

✔ Memorise the reaction patterns rather than isolated equations.

✔ Revise state symbols: (s), (l), (g), and (aq).

✔ Understand the difference between oxidation and reduction.

✔ Use scientific terms in descriptive answers.

✔ Draw neat labelled diagrams where required.

✔ Read NCERT activities and observations carefully.

Frequently Asked Questions (FAQs)

Q1. What is a chemical reaction?

A chemical reaction is a process in which one or more substances change into new substances with different properties.

Q2. Why should chemical equations be balanced?

Balanced equations follow the Law of Conservation of Mass by ensuring that the number of atoms of each element is equal on both sides.

Q3. What is the difference between oxidation and reduction?

Oxidation involves the addition of oxygen or removal of hydrogen, whereas reduction involves the removal of oxygen or addition of hydrogen.

Q4. What is a redox reaction?

A redox reaction is a chemical reaction in which oxidation and reduction occur simultaneously.

Q5. Why does iron rust?

Iron rusts because it reacts with oxygen and moisture present in the atmosphere.

Q6. What is galvanisation?

Galvanisation is the process of coating iron with zinc to prevent rusting.

Q7. What is rancidity?

Rancidity is the oxidation of fats and oils, causing food to develop an unpleasant smell and taste.

Q8. Why are chips packed with nitrogen gas?

Nitrogen is less reactive than oxygen. It prevents oxidation of oils, thereby reducing rancidity and increasing the shelf life of the product.

Q9. Which reaction is used in black-and-white photography?

The photolytic decomposition of silver chloride or silver bromide is used in traditional black-and-white photography.

Q10. Which chapter concepts are most important for the CBSE Board Exam?

Students should focus on:

• Balancing chemical equations
• Types of chemical reactions
• Oxidation and reduction
• Corrosion
• Rancidity
• Important chemical equations
• NCERT in-text and activity-based questions

Chapter Summary

In this chapter, you learned that chemical reactions are responsible for the formation of new substances with different properties. You studied how to represent reactions using chemical equations and why balancing these equations is essential to satisfy the Law of Conservation of Mass.

You explored the five major types of chemical reactions—combination, decomposition, displacement, double displacement, and redox reactions—and understood their significance through examples. The chapter also explained the concepts of oxidation, reduction, corrosion, rusting, galvanisation, and rancidity, highlighting their practical importance in everyday life.

A strong understanding of these concepts forms the foundation for future chemistry topics and plays a key role in success in the CBSE Class 10 Science examination.

💡 Did You Know?

The human body carries out millions of chemical reactions every minute. From producing energy in cells to repairing tissues and digesting food, life itself depends on continuous chemical reactions.

📘 Master CBSE Class 10 Science with the Complete Study Guide

Enjoyed these free notes? These chapter notes cover the core concepts, but board exam success requires much more than theory alone.

If you’re serious about scoring high in the CBSE Class 10 Science examination, the CBSE Class 10 Science Master Guide (2026–27 Edition) by Science World By Tushar Sir is designed to help you prepare with confidence.

🌟 What’s Inside the Complete Book?

✔ Complete chapter-wise theory with easy explanations
✔ NCERT concepts explained in simple language
✔ Mind Maps for quick revision
✔ Important definitions and key points
✔ Chapter-wise MCQs
✔ Assertion & Reason Questions
✔ Case-Based Questions
✔ Short & Long Answer Questions
✔ Practice Papers
✔ Exam Tips and Smart Revision Strategies

📚 Available Formats

📕 Paperback Edition
Perfect for classroom study, highlighting important points, and regular revision.

📱 eBook Edition
Study anytime on your mobile, tablet, or computer with instant access.

🎯 Who Should Buy This Book?

• CBSE Class 10 students
• Students preparing for Board Exams
• School examinations and unit tests
• Self-study learners
• Teachers and coaching institutes

⭐ Why Thousands of Students Choose Science World By Tushar Sir

At Science World By Tushar Sir, our goal is to make science simple, interesting, and exam-focused. Every chapter is prepared with concept clarity, structured learning, and board-oriented practice to help students build confidence and achieve better results.

Learn Smart • Practice Well • Score High

📚 Continue Learning

Next Chapter: Acids, Bases and Salts Class 10 Notes (Chapter 2)