Chemical Reactions and Equations

Chemical Reactions and Equations

• Word Equations: Show reactants (starting materials) and products (resulting materials)
• Balanced Equations: Represent chemical reactions accurately; the number of atoms of each element is equal on both sides
• Reaction Conditions: Indicate temperature, pressure, catalyst needed, use symbols (e.g., 340 atm, sunlight, Heat)
• Combination Reaction: Two or more reactants combine to form one product
  • Examples:
    • Burning of coal: C(s) + O₂(g) → CO₂(g)
    • Formation of water: 2H₂(g) + O₂(g) → 2H₂O(l)
    • Formation of calcium hydroxide: CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat

Exothermic Reactions

• Release heat with product formation
• Examples:
  • Burning of natural gas: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g) + Heat
  • Respiration: C₆H₁₂O₆(aq) + 6O₂(g) → 6CO₂(aq) + 6H₂O(l) + energy

Decomposition Reactions

• A compound splits into two or more simpler substances
  • Thermal decomposition:
    • Uses heat as energy for reaction
    • Examples:
      • 2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g)
      • CaCO₃(s) → CaO(s) + CO₂(g)
      • 2Pb(NO₃)₂(s) → 2PbO(s) + 4NO₂(g) + O₂(g)
  • Electrolytic decomposition:
    • Uses electricity as energy source
    • Example: 2H₂O(l) → 2H₂(g) + O₂(g)
  • Photolytic decomposition:
    • Requires sunlight as the energy source
    • Examples:
      • 2AgCl(s) → 2Ag(s) + Cl₂(g)
      • 2AgBr(s) → 2Ag(s) + Br₂(g)

Endothermic Reactions

• Require energy (heat, light, electricity) to break reactants

Displacement Reactions

• More reactive elements replace less reactive elements in a compound
• Examples:
  • Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
  • Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
  • Pb(s) + CuCl₂(aq) → PbCl₂(aq) + Cu(s)

Double Displacement Reactions

• New compounds form by exchanging ions between two compounds
• Forms a precipitate or an insoluble substance
• Example: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)

Oxidation

• Gaining oxygen during a reaction
• Example: 2Cu + O₂ → 2CuO

Reduction

• Gaining electrons or a decrease in oxidation state

Redox Reactions

• Combination of oxidation and reduction; one reactant gets oxidized while the other gets reduced

Acids, Bases and Salts

• Reaction of Metals with Acids: Acid + Metal → Salt + Hydrogen gas
• Reaction of Metal Carbonates/Metal Hydrogen Carbonates with Acids: Acid + Metal Carbonate/Metal Hydrogen Carbonate → Salt + CO₂ + H₂O
• Reaction of Acids and Bases With Each Other: Acid + Base → Salt + Water

Preparation of Sodium Hydroxide

• 2NaCl(aq) + 2H₂O(l) -> 2NaOH(aq) + Cl₂(g) + H₂(g)

Other Preparations

• Bleaching powder: Ca(OH)₂(aq) + Cl₂(g) → CaOCl₂(aq) + H₂O(I)
• Baking soda: NaCl + H₂O + CO₂ + NH₃ → NH₄Cl
• Washing soda: Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O
• Plaster of Paris: CaSO₄.2H₂O → CaSO₄.1/2H₂O + 3/2H₂O

Metals and Non-metals

• Reaction of Metals with Air: Metal + O₂ → Metal Oxide (e.g., 2Cu + O₂ → 2CuO)
• Reaction of Metals with Water: Metal + Water → Metal Hydroxide + Hydrogen
  • Some metals react violently with cold water, others are slower and need steam
• Amphoteric Oxides: React with both acids and bases (e.g., Al₂O₃)
• Electrolytic Reduction : Used to extract metals from their ores
• Extraction by Roasting: Heat metal ore with oxygen to produce metal oxide
• Extraction by Calcination: Heat metal carbonate to form metal oxide

Reaction of Metals with Acids:

• Metal + Acid → Salt + Hydrogen

Extracting Metals Low in the Activity Series:

• Heating ores (e.g., cinnabar = HgS) with oxygen to produce mercury(Hg)

Extracting Metals in the Middle of the Activity Series

• Roasting: heating ZnS + 02 → ZnO + SO₂
• Calcination: heating ZnCO3 → ZnO + CO₂

Extracting Metals Towards the Top of the Activity Series

• Electrolytic Reduction (e.g., Na, Mg, Ca are obtained this way)
• Uses electricity to reduce metal ions to their elemental state

This quiz covers the fundamentals of chemical reactions and equations, including word equations, balanced equations, and various types of reactions such as combination, exothermic, and decomposition reactions. Test your knowledge on the conditions and representations involved in chemical processes.