Chemical Reactions and Equations - Class 10 Notes

What is a Chemical Reaction?

• A process where one or more substances (reactants) transform into new substances (products).
• Examples include cooking food and rusting iron.

Chemical Equations

• Symbolic representation of a chemical reaction using symbols/formulas.
• Reactants: Substances undergoing change (e.g., Magnesium and Oxygen).
• Products: New substances formed (e.g., magnesium oxide when magnesium burns in air).
• Use of chemical formulas (e.g., H2O for water).

Writing a Chemical Equation

• Represented with symbols/formulae of reactants/products.
• States of matter: (s) solids, (l) liquids, (g) gases, (aq) aqueous.
• Reactants on the left (LHS), products on the right (RHS).
• Balanced Equation: Number of atoms for each element is the same on both sides.

Balancing Chemical Equations

• Law of Conservation of Mass: Atoms can't be created or destroyed.
• Use coefficients to balance the number of atoms for each element.
  • Example: Balancing Zn + HCl → ZnCl2 + H2 involves adjusting coefficients.
• Steps: Balance using maximum atoms on either side, adjust other elements, ensure equal atoms on both sides.

Types of Chemical Reactions

1. Combination Reaction

• Two or more reactants combine to form a single product.
• Examples:
  • Calcium oxide + water → Calcium hydroxide (exothermic).
  • Burning of coal (C + O2 → CO2).

2. Decomposition Reaction

• A single reactant breaks down into two or more products.
• Types:
  • Thermal Decomposition: Heating (e.g., ferrous sulphate to ferric oxide).
  • Photolytic Decomposition: Light (e.g., H2O2 to water and oxygen).
  • Electrolytic Decomposition: Electricity (e.g., electrolysis of water).

3. Displacement Reaction

• More reactive element displaces a less reactive element from a compound.
• Example: Iron with copper sulphate → Iron sulphate + Copper.

4. Double Displacement Reaction

• Ions of two compounds switch places forming new compounds.
• Example: Barium chloride + sodium sulphate → Barium sulphate + sodium chloride.

5. Endothermic and Exothermic Reaction

• Exothermic: Energy released (e.g., burning carbon).
• Endothermic: Energy absorbed (e.g., photosynthesis).

6. Oxidation and Reduction

• Oxidation: Loss of electrons or gain of oxygen.
• Reduction: Gain of electrons or loss of oxygen.
• Redox Reaction: Occurrence of oxidation and reduction together.

Effects of Oxidation in Everyday Life

1. Corrosion

• Metals react with moisture, oxygen leading to deterioration (e.g., rusting of iron).
• Examples:
  • Iron rusts to form Fe2O3.xH2O.
  • Copper forms a green oxide layer.

2. Rancidity

• Oxidation of fats/oils leads to bad taste and odor.
• Prevention: Store in airtight containers, refrigeration, use of antioxidants.

These notes aim to provide a comprehensive overview of chemical reactions and equations for Class 10 students, covering the fundamental concepts and examples necessary for understanding and examining chemical processes.