Class 10 Science Notes Chapter 1: Chemical Reactions and Equations

Chemical reactions are happening around us all the time, whether it is cooking food, rusting of iron, burning of fuel, or digestion in our body. In Class 10 Science Chemical Reactions and Equations is the first chemistry chapter that introduces students to these interesting changes.

These Class 10 Science Notes Chapter 1 Chemical Reactions and Equations explains all the key concepts in simple language, making revision quick and effective. From writing balanced chemical equations to understanding different types of chemical reactions, oxidation, corrosion and rancidity.

Topics Covered in Class 10 Science NOTES Chapter 1 Chemical Reactions and Equations 

What are Chemical Reactions	Types of Chemical Reactions
Characteristics of a Chemical Reaction	Combination Reaction
Chemical Equation	Decomposition Reaction
Types of Chemical Equations	Displacement Reaction
Symbols Used in Chemical Equations	Double Displacement Reaction
Balanced Chemical Equation	Precipitation Reaction
Steps to Balance a Chemical Equation	Corrosion
Importance of Balancing a Chemical Equation	Rancidity

Class 10 Science Chapter 1: Chemical Reactions and Equations NOTES

What are Chemical Reactions

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

In a chemical reaction, atoms rearrange themselves by breaking old chemical bonds and forming new ones, resulting in the formation of new substances.

General Representation

Reactants → Products

Examples of Chemical Reactions

• Burning of magnesium ribbon
• Rusting of iron
• Digestion of food
• Respiration
• Cooking food
• Formation of curd from milk

Characteristics of a Chemical Reaction

The following observations indicate that a chemical reaction has taken place:

• Change in colour
• Evolution of gas
• Formation of a precipitate
• Change in temperature
• Change in state
• Change in smell (in some reactions)

Example

When a magnesium ribbon is burnt in air, it produces a bright white flame and forms white magnesium oxide.

Chemical Equation

2Mg + O₂ → 2MgO

What is a Chemical Equation

A chemical equation is the symbolic representation of a chemical reaction using the chemical symbols and formulae of the substances involved.

It shows:

• Reactants
• Products
• Direction of the reaction
• Physical states of substances (solid, liquid, gas, aqueous)

Types of Chemical Equations

1. Word Equation

A chemical reaction represented using the names of substances.

Example

Hydrogen + Oxygen → Water

2. Chemical Equation

A reaction represented using chemical symbols and formulae.

Example

2H₂ + O₂ → 2H₂O

Symbols Used in Chemical Equations

Symbol	Meaning
+	Reacts with
→	Produces or forms
(s)	Solid
(l)	Liquid
(g)	Gas
(aq)	Aqueous solution
Δ	Heat is supplied

Balanced Chemical Equation

A balanced chemical equation is an equation in which the number of atoms of each element is the same on both the reactant and product sides.

Balancing an equation follows the Law of Conservation of Mass, which states that matter can neither be created nor destroyed during a chemical reaction.

Why is Balancing a Chemical Equation Important?

• Follows the Law of Conservation of Mass.
• Shows the correct number of atoms on both sides.
• Represents the reaction accurately.
• Helps in performing chemical calculations.

Steps to Balance a Chemical Equation

1. Write the unbalanced chemical equation.
2. Count the number of atoms of each element on both sides.
3. Add suitable coefficients to balance the atoms.
4. Recheck the equation to ensure all atoms are balanced.

Example

• Unbalanced Equation

H₂ + O₂ → H₂O

• Balanced Equation

2H₂ + O₂ → 2H₂O

Types of Chemical Reactions

Chemical reactions are classified based on how reactants are transformed into products.

1. Combination Reaction

Definition

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

General Equation

A + B → AB

Example

2Mg + O₂ → 2MgO

Another example:

CaO + H₂O → Ca(OH)₂

The reaction between calcium oxide and water releases heat, making it an exothermic reaction.

Quick Tip: Combination reactions always produce one product.

2. Decomposition Reaction

Definition

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

General Equation

AB → A + B

Decomposition reactions require energy in the form of heat, electricity, or sunlight.

Types of Decomposition Reactions

Thermal Decomposition occurs due to heat.

Example

CaCO₃ → CaO + CO₂

Electrolytic Decomposition occurs due to electricity.

Example

2H₂O → 2H₂ + O₂

Photolytic Decomposition occurs due to sunlight.

Example

2AgCl → 2Ag + Cl₂

Silver chloride decomposes in sunlight, which is why it is stored in dark-coloured bottles.

Quick Tip: One reactant gives multiple products.

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

Example

Zn + CuSO₄ → ZnSO₄ + Cu

Since zinc is more reactive than copper, it replaces copper from copper sulphate solution.

Quick Tip: The more reactive metal always displaces the less reactive metal.

4. Double Displacement Reaction

Definition

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

General Equation

AB + CD → AD + CB

Example

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

A white precipitate of barium sulphate is formed.

Precipitation Reaction

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

Quick Tip: Ion exchange occurs in double displacement reactions.

Corrosion

Corrosion is the gradual destruction of metals due to their reaction with air, moisture, or other chemicals.

Example

Rusting of iron:

4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O

Prevention of Corrosion

• Painting
• Galvanisation
• Alloying
• Oiling and greasing
• Electroplating

Preventing corrosion increases the life of metals and reduces economic losses.

Rancidity

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

Examples

• Chips becoming stale
• Butter developing a bad smell
• Cooking oil spoiling over time

Prevention of Rancidity

• Store food in airtight containers.
• Keep food away from sunlight.
• Refrigerate oily food.
• Add antioxidants.
• Pack food with nitrogen gas to prevent oxidation.