Major Categories of Chemical Reactions

Introduction

• Focus on recognizing patterns in chemical reactions.
• Main types of reactions to be discussed:
  • Synthesis (Combination) Reactions
  • Decomposition Reactions
  • Single Displacement (Replacement)
  • Double Displacement (Replacement)
  • Combustion

Synthesis (Combination) Reactions

• Definition: Two or more reactants combine to form one product (A + B -> AB).
• Examples:
  • Binary Ionic Compounds:
    • Sodium (Na) + Sulfur (S) -> Sodium Sulfide (Na₂S)
    • Key Steps:
      • Determine formula by crisscross method for charges.
      • Balance the equation: 2 Na + S -> Na₂S.
    • Phases: Pure ionic compounds are solid due to strong intermolecular forces.
  • Calcium and Oxygen Reaction:
    • Calcium (Ca) + Oxygen (O₂) -> Calcium Oxide (CaO)
    • Crisscross charges, reduce for empirical formula: CaO
    • Balance: 2 Ca + O₂ -> 2 CaO
  • Pattern: Metal + Non-metal -> Ionic Compound

Phases of Matter at Room Temperature

• Diatomic Gases: Hydrogen (H₂), Nitrogen (N₂), Oxygen (O₂), Fluorine (F₂), Chlorine (Cl₂)
• Noble Gases: Helium (He), Neon (Ne), Argon (Ar), etc.
• Liquids: Bromine (Br), Mercury (Hg)
• Solids: All other elements

Decomposition Reactions

• Definition: One substance splits into two or more substances (AB -> A + B).
• Example:
  • Mercury(II) Oxide Decomposition:
    • HgO (s) -> Hg (l) + O₂ (g)
    • Balance: 2 HgO -> 2 Hg + O₂
• Special Case: Metal Carbonates
  • Decomposition of Metal Carbonates:
    • Example: CuCO₃ -> CuO + CO₂
    • Pattern: Metal Carbonate -> Metal Oxide + CO₂
    • Practical Application:
      • Related to concrete production; CaCO₃ emits CO₂ as it dries, contributing to greenhouse gases.
      • Potential impact on climate change.

Conclusion

• Synthesis: Focus on predicting ionic compounds formed from metals and non-metals.
• Decomposition: Understanding of how compounds break apart, especially with carbonates.
• Important Reaction: Carbonate decomposition's tie to climate change due to CO₂ emissions from concrete.
• Key Skills:
  • Predict synthesis products.
  • Balance chemical equations.
  • Understand phases of elements at room temperature.