Chemical Reactions and Equations

Introduction to Chemical Reactions

• Examples in Daily Life:
  • Milk souring in the heat
  • Rusting of iron
  • Fermentation of grapes
  • Cooking and digestion of food
  • Respiration
• Definition: Change in chemical composition, indicating a chemical reaction.

Activities Demonstrating Chemical Reactions

• Activity 1.1: Burning magnesium ribbon in air to form magnesium oxide.
  • Observation: Dazzling white flame.
• Activity 1.2: Formation of hydrogen gas by reacting dilute sulfuric acid with zinc.
• Activity 1.3: Reaction of zinc with hydrochloric acid to produce zinc sulfate and hydrogen.

Recognizing Chemical Reactions

• Signs of a chemical reaction include:
  • Change in state
  • Change in color
  • Gas evolution
  • Temperature change

Chemical Equations

• Word Equations: Describe reactions in words. Example: Magnesium + Oxygen → Magnesium Oxide.
• Chemical Equations: Use chemical symbols (e.g., Mg + O2 → MgO).
• Balanced Equations: Must satisfy the law of conservation of mass.

Balancing Chemical Equations

• Use the hit-and-trial method:
  1. Write skeletal equation.
  2. Count atoms of each element.
  3. Balance one element at a time using coefficients.
  4. Ensure mass is conserved.

Types of Chemical Reactions

1. Combination Reactions

• Definition: Two or more substances combine to form one product.
• Example: CaO + H2O → Ca(OH)2

2. Decomposition Reactions

• Definition: A single compound breaks down into two or more simpler substances.
• Example: CaCO3 → CaO + CO2

3. Displacement Reactions

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

4. Double Displacement Reactions

• Definition: Exchange of ions between two compounds.
• Example: Na2SO4 + BaCl2 → BaSO4 + 2NaCl

5. Redox Reactions

• Oxidation: Gain of oxygen or loss of hydrogen.
• Reduction: Loss of oxygen or gain of hydrogen.
• Example: ZnO + C → Zn + CO

Effects of Chemical Reactions in Daily Life

1. Corrosion

• Metals react with environmental substances leading to damage.

2. Rancidity

• Oxidation of fats and oils makes food unpalatable.
• Prevention: Use of antioxidants, airtight containers.

Summary

• Chemical equations represent reactants, products, and their states.
• Equations must be balanced to comply with the conservation of mass.
• Various types of reactions: combination, decomposition, displacement, double displacement, and redox.

Exercises

• Questions on types of reactions, balancing equations, examples of daily life applications.