CBSE Class 10 Science Revision Notes Chapter 1 Chemical Reactions and Equations

CBSE Class 10 Science Revision Notes Chapter 1 explain chemical reactions, balanced equations, reaction types, redox reactions, corrosion and rancidity.

For CBSE 2026 Science, Chapter 1 Chemical Reactions and Equations builds the base for writing reactions, balancing atoms and reading observations.

Why does a magnesium ribbon turn into white ash, while an iron nail dipped in copper sulphate gets a brown coating? The NCERT Class 10 Science chapter Chemical Reactions and Equations begins with visible changes like these and turns them into chemical equations. Reactions such as 2Mg + O₂ → 2MgO, Zn + H₂SO₄ → ZnSO₄ + H₂, and Fe + CuSO₄ → FeSO₄ + Cu show how reactants form new products.

The 2026 NCERT chapter links each observation to a rule. Atoms are rearranged, equations are balanced by conservation of mass, and products may show gas formation, colour change, heat change or precipitate formation. The final part connects oxidation with rusting of iron and rancidity in oil-rich food.

Key Takeaways

• Magnesium burning: Magnesium burns with a dazzling white flame and forms white magnesium oxide.
• Conservation of mass: A balanced equation keeps the number of atoms of each element equal on both sides.
• Decomposition clue: Ferrous sulphate changes from green crystals and gives sulphur dioxide and sulphur trioxide on heating.
• Food oxidation: Chips packets are flushed with nitrogen to slow rancidity caused by oxidation of fats and oils.

CBSE Class 10 Science Revision Notes Chapter 1 Structure 2026

Chemical Reactions: How New Substances Are Formed

A chemical reaction takes place when the nature and identity of the original substance change. Milk turning sour, iron rusting and food getting digested are examples where new substances form.

In Chemical Reactions and Equations, these daily changes become the starting point for reactants, products and symbolic equations. The same idea supports most observations used in class 10 science chapter 1 notes.

Signs of a chemical reaction

A chemical reaction can be identified by any one of these changes:

• Change in state
• Change in colour
• Evolution of gas
• Change in temperature
• Formation of a precipitate

Examples:

1. Magnesium burns with a dazzling white flame and forms white magnesium oxide.
2. Zinc reacts with dilute sulphuric acid and releases hydrogen gas.
3. Lead nitrate reacts with potassium iodide and forms yellow lead iodide.
4. Calcium oxide reacts with water and releases heat.

Reactants and products

Reactants are the substances that take part in a chemical reaction. Products are the new substances formed after the reaction.

Example:

Magnesium + Oxygen → Magnesium oxide

Mg + O₂ → MgO

Magnesium and oxygen are reactants. Magnesium oxide is the product.

Chemical Equations: Writing Reactions in Symbolic Form

A chemical equation represents a chemical reaction using symbols and formulae. It is more precise than a sentence because it shows the reacting substances, products and direction of change.

The NCERT Class 10 Science chapter first uses word equations, then replaces names with chemical formulae. This shift helps students write shorter and more exact reaction statements.

Word equation

A word equation uses names of substances.

Example:

Magnesium + Oxygen → Magnesium oxide

The arrow shows the direction of the reaction. Reactants are written on the left side, and products are written on the right side.

Chemical equation

A chemical equation uses chemical formulae instead of names.

Example:

Mg + O₂ → MgO

This equation is a skeletal equation because the number of oxygen atoms is unequal on both sides. The left side has two oxygen atoms, while the right side has one oxygen atom.

Skeletal equation

A skeletal equation is an unbalanced chemical equation. It gives the correct formulae of reactants and products, but atoms are unequal on both sides.

Example:

Fe + H₂O → Fe₃O₄ + H₂

This equation needs balancing because iron and oxygen atoms are unequal on both sides.

Balanced Chemical Equations and Conservation of Mass

A balanced chemical equation follows the law of conservation of mass. The total number of atoms of each element remains the same before and after the reaction.

Chemical formulae are kept unchanged while balancing. Only coefficients are added before formulae.

Why chemical equations are balanced

Chemical equations are balanced because atoms are neither created nor destroyed in a chemical reaction. They rearrange to form new substances.

Example:

Skeletal equation:

Fe + H₂O → Fe₃O₄ + H₂

Balanced equation:

3Fe + 4H₂O → Fe₃O₄ + 4H₂

The balanced equation has 3 Fe atoms, 8 H atoms and 4 O atoms on both sides.

Balancing Fe and steam reaction

Step 1: Write the skeletal equation.

Fe + H₂O → Fe₃O₄ + H₂

Step 2: Balance oxygen first.

Fe + 4H₂O → Fe₃O₄ + H₂

Step 3: Balance hydrogen.

Fe + 4H₂O → Fe₃O₄ + 4H₂

Step 4: Balance iron.

3Fe + 4H₂O → Fe₃O₄ + 4H₂

Final balanced equation:

3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

Physical state symbols in equations

Physical state symbols show whether reactants and products are solid, liquid, gas or aqueous solution.

Example:

CaCO₃(s) → CaO(s) + CO₂(g)

This equation shows calcium carbonate and calcium oxide as solids. Carbon dioxide is released as a gas.

How Chemical Reactions Are Classified

Class 10 Science classifies chemical reactions by the way reactants change into products. The main patterns are combination, decomposition, displacement, double displacement and redox reactions.

Each pattern has a different clue. Some reactions form one product, some break one reactant, some replace elements, and some exchange ions.

Combination reactions and exothermic changes

A combination reaction forms one product from two or more reactants. The product has a new chemical identity.

Example:

CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat

Calcium oxide reacts with water to form calcium hydroxide. This reaction releases heat, so it is also exothermic.

Other examples:

C(s) + O₂(g) → CO₂(g)

2H₂(g) + O₂(g) → 2H₂O(l)

Exothermic reactions

An exothermic reaction releases heat with products. Respiration is an exothermic process because glucose breaks down with oxygen and releases energy.

Equation:

C₆H₁₂O₆(aq) + 6O₂(aq) → 6CO₂(aq) + 6H₂O(l) + Energy

Burning of natural gas is another exothermic reaction.

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

Decomposition reactions using heat, light and electricity

A decomposition reaction breaks one reactant into two or more simpler products. Energy is needed to break the bonds in the reactant.

Thermal decomposition uses heat.

CaCO₃(s) → CaO(s) + CO₂(g)

Ferrous sulphate also decomposes on heating.

2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g)

Electrolytic decomposition uses electricity.

2H₂O(l) → 2H₂(g) + O₂(g)

Photolytic decomposition uses light.

2AgCl(s) → 2Ag(s) + Cl₂(g)

Silver chloride turns grey in sunlight because silver metal forms.

Endothermic reactions

An endothermic reaction absorbs energy from the surroundings. Decomposition reactions usually need heat, light or electricity.

Example:

2AgBr(s) → 2Ag(s) + Br₂(g)

This reaction takes place in sunlight. It is used in black and white photography.

Displacement Reactions with Metal Reactivity

A displacement reaction takes place when a more reactive element removes a less reactive element from its compound. Iron placed in copper sulphate solution shows this reaction through a colour change.

The blue colour of copper sulphate fades, and copper deposits on the iron nail. This happens because iron is more reactive than copper.

Iron and copper sulphate reaction

Iron displaces copper from copper sulphate solution.

Equation:

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Iron forms iron sulphate, while copper separates as a brown deposit. This is a displacement reaction.

Other displacement reactions

Zinc and lead also displace copper from its compounds.

Examples:

Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

Pb(s) + CuCl₂(aq) → PbCl₂(aq) + Cu(s)

These reactions show that a more reactive metal can displace a less reactive metal from its salt solution.

Double Displacement and Precipitation Reactions

A double displacement reaction involves exchange of ions between two compounds. The reaction between sodium sulphate and barium chloride forms an insoluble white solid.

A precipitation reaction forms an insoluble solid from solutions. The insoluble solid is called a precipitate.

Barium chloride and sodium sulphate reaction

Sodium sulphate reacts with barium chloride to form barium sulphate and sodium chloride.

Equation:

Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)

Barium sulphate is a white insoluble precipitate. Sodium chloride remains in solution.

Lead nitrate and potassium iodide reaction

Lead nitrate reacts with potassium iodide to form lead iodide and potassium nitrate.

Equation:

Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq)

Lead iodide forms a yellow precipitate. This reaction is both double displacement and precipitation.

Oxidation and Reduction in Chemical Reactions

Oxidation and reduction occur together in a redox reaction. Class 10 explains these changes through gain or loss of oxygen and hydrogen.

A substance is oxidised when it gains oxygen or loses hydrogen. A substance is reduced when it loses oxygen or gains hydrogen.

Oxidation

Oxidation means gain of oxygen or loss of hydrogen.

Example:

2Cu + O₂ → 2CuO

Copper gains oxygen and forms black copper(II) oxide. So, copper is oxidised.

Reduction

Reduction means loss of oxygen or gain of hydrogen.

Example:

CuO + H₂ → Cu + H₂O

Copper(II) oxide loses oxygen and forms copper. So, copper(II) oxide is reduced.

Hydrogen gains oxygen and forms water. So, hydrogen is oxidised.

Redox reaction

A redox reaction involves oxidation and reduction in the same reaction.

Example:

ZnO + C → Zn + CO

Zinc oxide is reduced to zinc. Carbon is oxidised to carbon monoxide.

Another example:

MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂

Hydrochloric acid is oxidised to chlorine. Manganese dioxide is reduced to manganese chloride.

Corrosion and Rancidity as Everyday Oxidation Effects

Oxidation affects metals and food materials in daily life. Rusting and food spoilage show how slow chemical reactions can damage useful materials.

The NCERT Class 10 Science chapter Chemical Reactions and Equations uses corrosion and rancidity to connect oxidation with familiar changes. These examples also explain why metals are protected and oil-rich food is packed carefully.

Corrosion

Corrosion is the process in which a metal is attacked by substances like moisture, oxygen or acids. Rusting of iron is the most common example.

Iron articles form a reddish brown coating when exposed to moist air. Silver forms a black coating, and copper forms a green coating.

Corrosion damages car bodies, bridges, iron railings, ships and other metal objects. Painting, oiling and galvanisation reduce contact with air and moisture.

Rancidity

Rancidity occurs when fats and oils get oxidised. The smell and taste of food change due to oxidation.

Food containing fats and oils is stored in airtight containers to slow oxidation. Chips packets are flushed with nitrogen because nitrogen reduces contact with oxygen.

Antioxidants also slow rancidity. They protect oil-rich food materials from oxidation.

Important Chemical Equations for Revision

The main equations in Chemical Reactions and Equations come from observations, balancing practice and reaction classification. Magnesium burning, zinc reacting with dilute acid, barium sulphate precipitation and copper oxide reduction are important examples.

These equations help connect a visible change with the correct reaction type. They also support balanced chemical equation class 10 practice.

Other important equations:

1. Zn + H₂SO₄ → ZnSO₄ + H₂
2. 3Fe + 4H₂O → Fe₃O₄ + 4H₂
3. 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
4. 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
5. Fe + CuSO₄ → FeSO₄ + Cu
6. 2Cu + O₂ → 2CuO
7. CuO + H₂ → Cu + H₂O
8. Pb(NO₃)₂ + 2KI → PbI₂ + 2KNO₃

NCERT-Style Questions from Chemical Reactions and Equations

The exercise questions in Chapter 1 Chemical Reactions and Equations often ask for equations, observations and reaction types. A complete answer usually includes the balanced equation and the chemical reason behind the observation.

This section follows the same question pattern used in the NCERT Class 10 Science exercises. It supports class 10 science chapter 1 chemical reactions and equations notes without changing the textbook scope.

Q1. Why should magnesium ribbon be cleaned before burning?

Magnesium ribbon is cleaned to remove the oxide layer from its surface.

Explanation:

Magnesium reacts with oxygen in air and forms a thin magnesium oxide coating. Cleaning with sandpaper exposes fresh magnesium.

Equation:

2Mg + O₂ → 2MgO

Q2. Balance: Hydrogen + Chlorine → Hydrogen chloride

The balanced equation is:

H₂ + Cl₂ → 2HCl

Explanation:

There are 2 hydrogen atoms and 2 chlorine atoms on both sides. The equation follows conservation of mass.

Q3. What happens when zinc reacts with dilute sulphuric acid?

Zinc reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas.

Equation:

Zn + H₂SO₄ → ZnSO₄ + H₂

Observation:

Gas bubbles appear near zinc granules. The test tube may feel warm.

Q4. Why does copper sulphate solution change colour with an iron nail?

Iron displaces copper from copper sulphate solution.

Equation:

Fe + CuSO₄ → FeSO₄ + Cu

The blue colour fades because copper sulphate changes into iron sulphate. Copper deposits on the iron nail.

Q5. Identify oxidation and reduction in CuO + H₂ → Cu + H₂O.

Copper(II) oxide is reduced because it loses oxygen. Hydrogen is oxidised because it gains oxygen.

Equation:

CuO + H₂ → Cu + H₂O

This is a redox reaction because oxidation and reduction occur together.

Important Terms in Chemical Reactions and Equations

The chapter uses fixed terms in definitions, observations and equation-based answers. These terms help in one-mark answers and reaction identification.

Important terms from the NCERT Class 10 Science chapter include reactants, products, skeletal equation, balanced equation, precipitate, oxidation and reduction.

Reactants

Reactants are substances that undergo chemical change in a reaction.

Example:

In Mg + O₂ → MgO, magnesium and oxygen are reactants.

Products

Products are new substances formed in a chemical reaction.

Example:

In Mg + O₂ → MgO, magnesium oxide is the product.

Skeletal equation

A skeletal equation is an unbalanced chemical equation.

Example:

Mg + O₂ → MgO

Balanced equation

A balanced equation has equal atoms of each element on both sides.

Example:

2Mg + O₂ → 2MgO

Precipitate

A precipitate is an insoluble solid formed during a reaction in solution.

Example:

BaSO₄ is the white precipitate in Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl.

Oxidation

Oxidation means gain of oxygen or loss of hydrogen.

Example:

Copper is oxidised in 2Cu + O₂ → 2CuO.

Reduction

Reduction means loss of oxygen or gain of hydrogen.

Example:

Copper(II) oxide is reduced in CuO + H₂ → Cu + H₂O.

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