📘 Class 10 Science – Chapter: Chemical Reactions and Equations Notes

✨ Introduction to Chemical Reactions

• A chemical reaction involves the transformation of one or more substances into new substances.

• Indications of chemical reactions:

  • Change in color

  • Change in temperature

  • Evolution of gas

  • Formation of precipitate

Example: Rusting of iron, burning of magnesium.

🔹 Chemical Equations

• A chemical equation is a symbolic representation of a chemical reaction.

• Reactants: Substances that react.

• Products: New substances formed.

Example:
Magnesium + Oxygen → Magnesium oxide
Mg + O₂ → MgO

🔹 Balanced Chemical Equation

• Follows the Law of Conservation of Mass: mass of reactants = mass of products.

• Atoms of each element must be balanced on both sides.

Example:
Unbalanced: Fe + H₂O → Fe₃O₄ + H₂
Balanced: 3Fe + 4H₂O → Fe₃O₄ + 4H₂

🔹 Types of Chemical Reactions

● Combination Reaction

• Two or more reactants combine to form a single product.

Example:
CaO + H₂O → Ca(OH)₂

● Decomposition Reaction

• A single compound breaks into two or more simpler substances.

• Requires energy (heat, light, electricity).

Example:
2H₂O → 2H₂ + O₂ (Electrolysis)

● Displacement Reaction

• A more reactive element displaces a less reactive one from its compound.

Example:
Zn + CuSO₄ → ZnSO₄ + Cu

● Double Displacement Reaction

• Exchange of ions between two compounds forming new compounds.

Example:
Na₂SO₄ + BaCl₂ → BaSO₄⬇ + 2NaCl

● Redox Reaction

• Involves oxidation (loss of electrons) and reduction (gain of electrons).

Example:
Zn + CuO → ZnO + Cu

Zn is oxidized, CuO is reduced.

🔹 Exothermic and Endothermic Reactions

🔹 Corrosion and Rancidity

● Corrosion

• Gradual destruction of metals due to reactions with moisture, air.

• Example: Rusting of iron:
  Fe + O₂ + H₂O → Fe₂O₃.xH₂O

● Rancidity

• Oxidation of oils and fats causing bad smell and taste.

• Preventive measures:

  • Refrigeration

  • Using antioxidants

  • Storing in airtight containers

🔹 Important Symbols Used in Chemical Equations

Let me know if you want me to add:

• Reaction mechanism diagrams

• Step-by-step balancing examples

• Practice exercises with solutions