Overview
This lecture introduces five main types of chemical reactions—synthesis, decomposition, combustion, single replacement, and double replacement—explaining their general formulas, real-life examples, and significance in daily life.
Synthesis (Combination) Reactions
- Two or more substances combine to form a single product.
- General formula: A + B → AB.
- Example: Aluminum reacts with iodine (after oxide layer is removed) to form aluminum iodide.
- Photosynthesis is a synthesis reaction where plants create glucose and oxygen.
Decomposition Reactions
- One substance breaks down into two or more separate substances.
- General formula: AB → A + B.
- Example: Hydrogen peroxide decomposes into water and oxygen, sped up by a catalyst.
- Airbags use decomposition of sodium azide to rapidly release gas and inflate.
Combustion Reactions
- A substance reacts with oxygen, releasing energy as heat or light.
- Typically produces carbon dioxide (CO₂) and water (H₂O) with organic compounds.
- Example: Methane bubbles combust to form CO₂ and water vapor.
- Propane combustion is used in BBQ grills for cooking.
Single Replacement (Displacement) Reactions
- One element replaces another in a compound.
- General formula: A + BC → AC + B.
- Example: Copper replaces silver in silver nitrate, forming copper(II) nitrate and silver crystals.
- Thermite reactions, a type of single replacement, produce molten metal for railway track repairs.
Double Replacement (Displacement) Reactions
- Positive ions of two compounds switch places to form two new compounds.
- General formula: AB + CD → AD + CB.
- One product is usually a gas, water, or precipitate.
- Example: Potassium iodide reacts with lead(II) nitrate to form yellow lead(II) iodide precipitate.
- Antacids use double replacement to neutralize stomach acid and relieve heartburn.
Key Terms & Definitions
- Synthesis Reaction — Two or more substances combine to form a new compound.
- Decomposition Reaction — One compound breaks down into simpler substances.
- Combustion Reaction — Substance reacts with oxygen to release energy (heat/light).
- Single Replacement Reaction — One element replaces another in a compound.
- Double Replacement Reaction — Two compounds exchange ions to form new compounds.
- Catalyst — Substance that speeds up a chemical reaction without being consumed.
Action Items / Next Steps
- Review and memorize the five types of reactions and their general formulas.
- Prepare examples for each reaction type for class discussion.
- Complete assigned textbook readings on chemical reactions.