Chemical Reactions and Equations

Introduction

• Everyday phenomena involve chemical reactions:
  • Milk spoiling, iron rusting, fermentation of grapes, cooking and digestion of food.
• Chemical reactions: Change in identity of substances, distinguished from physical changes.
• Indicators of chemical reactions:
  • Change in state
  • Change in color
  • Evolution of gas
  • Change in temperature

Activities Demonstrating Chemical Reactions

Activity 1.1 - Burning Magnesium

• Burn magnesium ribbon; observe white powder formation (magnesium oxide).
• Represents a chemical reaction: Magnesium + Oxygen → Magnesium oxide.

Activity 1.2 - Zinc and Acid Reaction

• Zinc reacts with dilute sulphuric acid; hydrogen gas is evolved.
• Observations: Temperature change, zinc dissolves.

Activity 1.3 - Lead Nitrate and Potassium Iodide

• Mix solutions; observe precipitate formation.
• Reaction: Lead nitrate + Potassium iodide → Lead iodide + Potassium nitrate.

Writing and Balancing Chemical Equations

• Chemical reactions can be represented by word equations and chemical equations.
• Chemical Equation: Symbols of reactants and products.
• Law of Conservation of Mass requires balancing equations.
• Example:
  • Unbalanced: Fe + H2O → Fe3O4 + H2
  • Balanced: 3Fe + 4H2O → Fe3O4 + 4H2

Types of Chemical Reactions

Combination Reaction

• Two or more substances combine to form a single product.
• Example: Calcium oxide + Water → Calcium hydroxide (exothermic reaction).

Decomposition Reaction

• A single compound breaks down into two or more products.
• Example: 2FeSO4 → Fe2O3 + SO2 + SO3 (thermal decomposition).

Displacement Reaction

• An element displaces another element in a compound.
• Example: Fe + CuSO4 → FeSO4 + Cu

Double Displacement Reaction

• Exchange of ions between two compounds.
• Precipitation reaction as a subtype.
• Example: Na2SO4 + BaCl2 → BaSO4 + 2NaCl

Redox Reactions

• Involve transfer of electrons/oxygen.
• Oxidation: Gain of oxygen or loss of hydrogen.
• Reduction: Loss of oxygen or gain of hydrogen.
• Example: CuO + H2 → Cu + H2O

Effects of Oxidation in Daily Life

Corrosion

• Metals are corroded by moisture, air, etc.
• Example: Rusting of iron.

Rancidity

• Oxidation of fats and oils leads to spoilage.
• Prevention by using airtight containers or gases like nitrogen.

Summary

• Chemical equations represent reactants, products, and states.
• Balancing equations ensures the same number of atoms on both sides.
• Various types of reactions include combination, decomposition, displacement, and double displacement.
• Reactions can be endothermic or exothermic.
• Redox reactions involve oxidation and reduction processes.

Exercises

• Multiple exercises to practice balancing equations, identifying types of reactions, and understanding the application of chemical concepts in real life.