CHEMICAL REACTIONS AND EQUATIONS

Page 1: Chemical Reactions and Equations

Balancing Equations

  • Follow the law of conservation of mass

  • Chemical Reaction: Process in which new substances with new properties are formed

  • Word Equation: Written in terms of words describing the reaction

  • Skeletal Chemical Reaction: Represents the reactants and products in a chemical reaction but is unbalanced

  • Balanced Chemical Equation: Same number of atoms of each element on the left-hand side (LHS) and right-hand side (RHS)

    • Examples of changes:

      • Physical Change: No new substances formed (e.g., melting of ice, cutting paper)

      • Chemical Change: New substances formed (e.g., rusting of iron, burning of wood)

Types of Chemical Reactions

  • Combination Reaction: Two or more elements react to form a single product

    • Example: Mg + O2 → 2MgO (produces heat and light)

  • Reversible Reactions: Can proceed in both forward and backward directions

  • Irreversible Reactions: Only proceed in one direction (e.g., rusting, burning)

Characteristics of Chemical Reactions

  • Exothermic Reactions: Release heat (burning magnesium ribbon)

    • Observations:

      • Change in color (e.g., burning magnesium produces white light)

      • Production of hissing sound and bubbles (e.g., strong reactions)

  • Endothermic Reactions: Absorb heat and require energy input

    • Observations: Change in state, temperature changes observed during process (e.g., decomposition of compounds)

Common Reactions Explained

  • Burning of Natural Gas (Combustion Reaction): CH4 + O2 → CO2 + H2O + Energy

  • Photosynthesis Process: 6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2

  • Formation of Precipitate: eg: CaO + H2O → Ca(OH)2

Page 2: Important Concepts

Precautions and Redox Reactions

  • Maintain a safe distance while smelling gases

  • Redox Reaction: Involves simultaneous oxidation and reduction

    • Oxidation: Loss of electrons; Reduction: Gain of electrons

    • Example: Heating Lead Nitrate results in: 2Pb(NO3)2 → 4PbO + 4NO2 + O2

    • Observations include brown fumes of NO2

Electrolysis of Water

  • Reaction at Anode: Oxygen is produced (2H2O → 2H2 + O2)

  • Reaction at Cathode: Hydrogen is produced

  • Observations: Volume ratio of H2 to O2 is 2:1

    • Acid is added to act as an electrolyte for conductivity

Displacement and Double Displacement Reactions

  • Displacement Reaction: A more reactive metal displaces a less reactive metal from its compound (e.g., Fe + CuSO4 → FeSO4 + Cu)

    • Prevention of rusting includes methods such as painting and oiling

  • Double Displacement Reaction: New substances formed by the mutual exchange of ions between two compounds

    • Example: Na2 + BaCl2 → BaSO4 + 2NaCl

    • Example: 2KI + Pb(NO3)2 → PbI2 (yellow precipitate) + 2KNO3

Prevention Tips for Corrosion

  • Use of antioxidants to inhibit oxidation

  • Packaging methods such as filling with inert gases (e.g., nitrogen or helium)

  • Refrigeration and use of airtight containers to prevent exposure to air

Key Takeaways

  • Chemical reactions can be classified based on energy changes (exothermic/endothermic) and types (combination, decomposition, displacement, double displacement).

  • Observations during chemical reactions are key indicators to understand the reaction types and their mechanisms.