CH 01: Chemical Reactions and Equations of Class 10th Science

Chapter 1: Chemical Reactions and Equations

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Topics in the Chapter

• Introduction
• Chemical reaction
• Chemical equation
• Balanced chemical equation
• Types of chemical reactions
• Corrosion
• Rancidity

Introduction

→ Most of the substances around us undergo various changes. Some changes are temporary with no new substance formed, called physical changes.

→ Other changes result in a new substance where the reactant loses its identity to form a product, called chemical changes.

Chemical Reaction

→ A chemical reaction is the process in which two or more substances react to form a new substance with different properties.

→ Signs of a chemical reaction include:

• Change in state
• Change in color
• Evolution of gas
• Change in temperature

Chemical Equation

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

Magnesium + Oxygen → Magnesium Oxide

(Reactant) → (Product)

Balanced Chemical Equation

→ A balanced chemical equation ensures the number of atoms of each element is the same on both sides of the equation.

Zn + H₂SO₄ → ZnSO₄ + H₂

3Fe (s) + 4H₂O (g) → Fe₃O₄ (s) + 4H₂ (g)

Types of Chemical Reactions

1. Combination Reaction

→ Two or more substances combine to form a single product.

CaO (s) + H₂O (l) → Ca(OH)₂ (aq)

C (s) + O₂ (g) → CO₂ (g)

2. Exothermic Reaction

→ A reaction that releases energy in the form of heat or light.

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

3. Endothermic Reaction

→ A reaction that absorbs heat and cools the surroundings.

4. Decomposition Reaction

→ A single reactant breaks down to yield two or more products.

• Thermal decomposition: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
• Electrolysis: 2H₂O → 2H₂ + O₂
• Photochemical reaction: 2AgBr → 2Ag + Br₂

5. Displacement Reaction

→ One element displaces another from its compound.

Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)

6. Double Displacement Reaction

→ Exchange of ions between two compounds.

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

7. Redox Reaction

→ Involves transfer of electrons from one substance to another.

→ Oxidation: Loss of electrons or increase in oxidation state.

→ Reduction: Gain of electrons or decrease in oxidation state.

ZnO + C → Zn + CO

Effects of Oxidation Reactions in Daily Life

1. Corrosion

→ Gradual destruction of metals due to their reaction with oxygen and moisture in the environment.

→ Example: Rusting of iron.

Fe₂O₃.nH₂O (Hydrated iron oxide)

2. Rancidity

→ Process where fats and oils in food become rancid due to oxidation, resulting in unpleasant odor and taste.

→ Preventive methods: Adding antioxidants, airtight storage, refrigeration, etc.