Chemical Reactions and Equations

Introduction to Chemical Changes

• Chemical changes alter the chemical nature of substances.
• Examples:
  • Milk souring at room temperature.
  • Rust formation on an iron tawa in moisture.
  • Fermentation of grapes producing alcohol.
  • Cooking and digestion altering texture and nutrients.
  • Respiration oxidizes food to release energy.

Examples of Chemical Reactions

• Magnesium Ribbon Burning: Burnt in oxygen, forms magnesium oxide.
• Potassium Iodide and Lead Nitrate: Forms lead iodide precipitate.
• Zinc and Dilute HCl/H2SO4: Evolves hydrogen gas and heat.

Observations in Chemical Reactions

• State change, color change, gas evolution, temperature change indicate reactions.

Chemical Equations

• Word Equations: Description of reactions (e.g., Magnesium + Oxygen → Magnesium Oxide)
• Reactants and Products: Reactants (left), Products (right), separated by an arrow.

Balancing Chemical Equations

• Law of Conservation of Mass: Mass of reactants = Mass of products.
• Steps to Balance:
  1. Enclose chemical formulas in boxes.
  2. Tabulate atoms of elements on both sides.
  3. Focus on substances with maximum atoms.
  4. Adjust coefficients to balance atoms.
  5. Check balanced equation.
  6. Specify physical states (g, l, aq, s).

Types of Chemical Reactions

1. Combination Reaction

• Two or more reactants form a single product.
• Example: Calcium oxide + Water → Calcium hydroxide
• Exothermic (heat-releasing) reactions.

2. Decomposition Reaction

• A single compound breaks into simpler substances.
• Thermal Decomposition: Heat-induced breakdown (e.g., Ferrous sulfate).
• Electrolytic Decomposition: Electricity-induced (e.g., Water electrolysis).
• Photolytic Decomposition: Light-induced (e.g., Silver chloride breakdown).

3. Displacement Reaction

• More reactive element displaces a less reactive one.
• Example: Iron + Copper sulfate → Iron sulfate + Copper

4. Double Displacement Reaction

• Exchange of ions between two compounds.
• If precipitate forms, it's a precipitation reaction.

5. Oxidation and Reduction (Redox) Reactions

• Oxidation: Gain of oxygen.
• Reduction: Loss of oxygen.
• Example: Copper oxide + Hydrogen → Copper + Water (Redox reaction)

Effects of Oxidation Reactions

Corrosion

• Metals corroded by moisture and acids.
• Examples: Rusting of iron, tarnishing of silver.

Rancidity

• Oxidation of fats and oils leading to smell/taste change.
• Prevention: Antioxidants, airtight containers, nitrogen packing.

Conclusion

• Understanding chemical reactions and equations is crucial for grasping chemical processes.
• Important for applications in day-to-day life.