Chemical Reactions and Equations

Daily Life Situations and Chemical Changes

• Milk spoiling, iron rusting, fermentation of grapes, cooking, digestion, and respiration all involve chemical changes.
• Chemical reactions involve changes in the nature and identity of substances.

Observations Indicating Chemical Reactions

• Change in state
• Change in color
• Evolution of gas
• Change in temperature

Activities Demonstrating Chemical Reactions

• Activity 1.1: Burning of magnesium ribbon produces magnesium oxide.
• Activity 1.2: Formation of hydrogen gas by reacting zinc with dilute sulphuric acid.

Chemical Equations

• Word Equations: Long descriptions can be simplified using word equations, e.g., Magnesium + Oxygen -> Magnesium oxide.
• Skeletal Chemical Equations: Use chemical formulas for a concise representation, e.g., Mg + O2 -> MgO.
• Balanced Chemical Equations: Follow the law of conservation of mass; the total mass of reactants equals the total mass of products.
  • Example: Zn + H2SO4 -> ZnSO4 + H2
  • Balancing with coefficients ensures atom count equality on both sides.

Types of Reactions

Combination Reactions

• Two or more substances combine to form one product.
• Example: CaO + H2O -> Ca(OH)2 (Exothermic reaction)

Decomposition Reactions

• Single substance breaks down into two or more substances.
• Thermal Decomposition: Involves heat, e.g., CaCO3 -> CaO + CO2.

Displacement Reactions

• One element displaces another from its compound.
• Example: Fe + CuSO4 -> FeSO4 + Cu

Double Displacement Reactions

• Exchange of ions between two compounds.
• Precipitation Reaction: Produces an insoluble precipitate, e.g., Na2SO4 + BaCl2 -> BaSO4 + 2NaCl.

Redox Reactions

• Involve oxidation (gain of oxygen/loss of hydrogen) and reduction (loss of oxygen/gain of hydrogen).
• Example: CuO + H2 -> Cu + H2O

Everyday Effects of Reactions

Corrosion

• Metals corrode due to environmental exposure, e.g., rusting of iron.

Rancidity

• Oxidation of fats/oils leads to spoilage.
• Prevention methods include antioxidants and airtight containers.

Summary Points

• Chemical reactions involve changes in the substances' nature.
• Equations must be balanced to reflect the law of conservation of mass.
• Various types of reactions include combination, decomposition, displacement, and redox reactions.
• Real-world examples of reactions include corrosion and rancidity.

Exercises

• Includes practice on identifying types of reactions, balancing chemical equations, and understanding the practical implications of chemical reactions.