Chemical Reactions and Equations: Lecture Notes

Introduction

• Warm welcome to students.
• Overview of the session: Chemical Reaction and Equations.
• Purpose: Quick revision and important topics for CBSE Class 10.

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Chemical Reactions in Daily Life

• Examples of Chemical Changes:
  • Curdling of milk (Lactic acid formation from lactose).
  • Rusting of iron nails (Formation of hydrated iron oxide).
  • Importance of recognizing chemical changes in everyday life.

Definition of Chemical Reaction

• A process where one or more substances (reactants) undergo a change to form new substances (products) with different properties.
• Observable signs of chemical reactions include:
  • Change in state (e.g., gas to solid).
  • Change in color (e.g., blue copper sulfate turning green).
  • Evolution of gas (e.g., zinc reacting with sulfuric acid).
  • Change in temperature (exothermic and endothermic reactions).
  • Formation of precipitate (e.g., mixing of lead nitrate and potassium iodide).

Writing Chemical Equations

• Skeletal Equations: Basic representation using symbols and formulas.
• Balanced Equations: Ensure the number of atoms is equal on both sides, adhering to the Law of Conservation of Mass.
  • Coefficients are used to balance equations (e.g., 2H₂ + O₂ → 2H₂O).

Types of Chemical Reactions

1. Combination Reaction:
   • Two or more reactants combine to form a single product.
   • Example: H₂ + Cl₂ → 2HCl.
2. Decomposition Reaction:
   • A single substance breaks down into two or more simpler substances.
   • Types:
     • Thermal Decomposition (heat required).
     • Electrolysis (electricity required).
     • Photodecomposition (light required).
3. Displacement Reaction:
   • A more reactive element displaces a less reactive element from its compound.
   • Example: Zn + CuSO₄ → ZnSO₄ + Cu.
4. Double Displacement Reaction:
   • Exchange of ions between two compounds.
   • Example: Na₂SO₄ + BaCl₂ → BaSO₄ (precipitate) + 2NaCl.
5. Redox Reaction:
   • Simultaneous oxidation and reduction occur in the same reaction.
   • Example: Cu + O₂ → CuO (Cu is oxidized, O₂ is reduced).

Oxidation and Reduction

• Oxidation: Addition of oxygen or removal of hydrogen; loss of electrons.
• Reduction: Removal of oxygen or addition of hydrogen; gain of electrons.
• Reducing agent: substance that gets oxidized and causes reduction in another.
• Oxidizing agent: substance that gets reduced and causes oxidation in another.

Corrosion and Rancidity

• Corrosion: Degradation of metals due to chemical reactions with environmental elements (e.g., rusting of iron).
• Rancidity: Oxidation of fats and oils leading to bad smell and taste in food.
  • Prevention methods: Use of antioxidants, storing in airtight containers, refrigeration.

Conclusion

• Summary of chemical reactions and importance in daily life.
• Encouragement to visit Vedantu platform for more learning and revision.
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