Overview
This lecture covers how to identify and classify the main types of chemical reactions, including their general forms, key features, and common examples.
Combustion Reactions
- Combustion involves a substance reacting with oxygen to produce carbon dioxide (CO₂) and water (H₂O), releasing heat.
- Reactants usually include a hydrocarbon and oxygen; products are always CO₂ and H₂O.
- Example: C₈H₁₈ + O₂ → CO₂ + H₂O (octane combustion).
Synthesis (Combination) Reactions
- Two or more simpler substances combine to form a more complex compound.
- General form: A + B → AB.
- Can involve elements or compounds as reactants.
- Example: Mg + O₂ → MgO.
Decomposition Reactions
- A single compound breaks down into two or more simpler substances.
- General form: AB → A + B.
- Often requires heat or electricity.
- Example: CaCO₃ (heated) → CaO + CO₂.
Single Replacement (Single Displacement) Reactions
- An element replaces another element in a compound.
- General form: A + BC → AC + B.
- Usually a metal replaces another metal, or a nonmetal replaces another nonmetal.
- Example: Zn + CuCl₂ → ZnCl₂ + Cu.
Double Replacement (Double Displacement) Reactions
- Two compounds exchange ions to form two new compounds.
- General form: AB + CD → AD + CB.
- Includes several subtypes:
- Precipitation: formation of an insoluble solid.
- Acid-base neutralization: acid + base → salt + water.
- Gas evolution: formation of a gas product.
- Example: AgNO₃ + NaCl → AgCl (s) + NaNO₃.
Redox Reactions
- Involve transfer of electrons (oxidation and reduction).
- All combustion and single replacement reactions are redox.
- Some synthesis and decomposition reactions are redox if pure elements are involved.
- Double replacement reactions are not redox.
Key Terms & Definitions
- Combustion Reaction — A reaction with O₂ producing CO₂ and H₂O, releasing heat.
- Synthesis (Combination) Reaction — Two or more reactants form one product.
- Decomposition Reaction — A compound breaks into simpler substances.
- Single Replacement Reaction — One element replaces another in a compound.
- Double Replacement Reaction — Exchange of ions between two compounds.
- Precipitation Reaction — Double replacement that forms an insoluble solid.
- Acid-Base Neutralization — Acid reacts with base to form water and salt.
- Gas Evolution Reaction — Double replacement yielding a gaseous product.
- Redox Reaction — Reaction involving electron transfer.
Action Items / Next Steps
- Practice classifying given reactions by type.
- Review any homework or textbook sections on chemical reaction types.
- Memorize general reaction forms and key identifying features.