Chapter 1: Chemical Reactions and Equations

Introduction to Chemical Reactions

• Examples of daily life situations where chemical changes occur:
  • Milk left at room temperature
  • Iron exposed to humidity
  • Fermentation of grapes
  • Cooking and digestion of food
  • Respiration
• Chemical reactions involve changes in the nature and identity of substances.
• Indicators of chemical reactions:
  • Change in state, color
  • Evolution of gas
  • Change in temperature

Activities Demonstrating Chemical Reactions

Activity 1.1: Burning Magnesium

• Burn magnesium ribbon and observe formation of magnesium oxide.
• Safety precautions: Use tongs, wear eyeglasses.

Activity 1.2: Zinc and Dilute Sulphuric Acid

• Reaction produces hydrogen gas.
• Observe temperature change and gas evolution.

Activity 1.3: Zinc and Hydrochloric Acid

• Produces zinc sulfate and hydrogen gas.
• Emphasizes the concepts of reactants and products.

Chemical Equations

• Chemical reactions can be represented by word and chemical equations.
  • Word-equation example: Magnesium + Oxygen → Magnesium oxide
• Introduction to chemical formulas in equations.
• Importance of balancing chemical equations:
  • Law of conservation of mass: Atoms must be balanced on both sides.
  • Balanced equations provide stoichiometric ratios.

Balancing Chemical Equations

• Example: Fe + H2O → Fe3O4 + H2
  • Step-by-step method using hit-and-trial.
  • Introduction of physical states in equations for more information.

Types of Chemical Reactions

Combination Reactions

• Two or more substances combine to form a single product.
• Example: Calcium oxide reacts with water to form calcium hydroxide.

Decomposition Reactions

• A single compound breaks down into two or more simpler substances.
• Thermal decomposition examples:
  • Ferrous sulfate decomposition
  • Calcium carbonate decomposition into lime and carbon dioxide.

Displacement Reactions

• An element displaces another element in a compound.
• Example: Iron displaces copper in copper sulfate solution.

Double Displacement Reactions

• Exchange of ions between two compounds.
• Example: Na2SO4 + BaCl2 → BaSO4 + 2NaCl, forming a precipitate.

Oxidation and Reduction (Redox Reactions)

• Involves gaining or losing of oxygen or hydrogen.
• Example: CuO + H2 → Cu + H2O
• Explanation of oxidation and reduction processes in reactions.

Everyday Effects of Reactions

Corrosion

• Metal deterioration due to environmental effects.
• Example: Rusting of iron.

Rancidity

• Oxidation of fats and oils leading to unpleasant smell or taste.
• Prevention by using antioxidants or airtight containers.

Conclusion

• Importance of balanced chemical equations and their representation.
• Overview of combination, decomposition, exothermic, endothermic, displacement, and redox reactions.
• Importance of understanding reaction types for practical applications.

Exercises and Questions

• Questions to reinforce the concepts learned, such as identifying reaction types, balancing equations, and explaining corrosion and rancidity.
• Encourage practical applications and deeper understanding through problem-solving.