Overview
This lecture covers various types of chemical reactions, focusing on gas-producing double displacement reactions, single and double displacement, decomposition, combustion, synthesis, and the recognition of redox reactions.
Double Displacement Gas Production Reactions
- Double displacement reactions can produce unstable compounds that decompose into water and a gas.
- Classic examples: mixing vinegar (acetic acid) and baking soda (sodium bicarbonate) produces CO₂ bubbles.
- If reaction forms H₂CO₃, it decomposes into H₂O and CO₂ gas.
- If H₂SO₃ forms, it breaks down into H₂O and SO₂ gas.
- Formation of NH₄OH leads to H₂O and NH₃ gas.
- Example: CaCO₃ + 2HCl → CaCl₂ + H₂CO₃ (which decomposes to H₂O + CO₂).
Single Displacement Reactions
- A more active element replaces a less active one (cation replaces cation or anion replaces anion).
- Example: Fe + CuSO₄ → FeSO₄ + Cu (iron replaces copper).
- For halogens: F₂ replaces Cl⁻, Cl₂ replaces Br⁻, Br₂ replaces I⁻.
- No reaction occurs if the replacing element is lower in reactivity.
Synthesis and Decomposition Reactions
- Synthesis: two elements combine to form one compound (e.g., 2Na + Cl₂ → 2NaCl).
- Decomposition: a compound breaks down into simpler substances, often producing a gas.
- Decomposition may need heat, electricity, or a catalyst.
Combustion Reactions
- Hydrocarbons or alcohols react with O₂ to form CO₂ and H₂O.
- Example: CH₄ + 2O₂ → CO₂ + 2H₂O.
- Ethanol combustion: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.
Reactions of Oxides with Water
- Non-metal oxides + water → acids (e.g., SO₂ + H₂O → H₂SO₃).
- Metal oxides + water → bases (e.g., MgO + H₂O → Mg(OH)₂).
Redox (Oxidation-Reduction) Reactions
- Occur when oxidation states change due to electron transfer.
- Metals lose electrons (oxidized); non-metals gain electrons (reduced).
- Many single displacement, synthesis, and decomposition reactions are redox reactions.
- Example: KClO₃ decomposing to KCl and O₂ is a redox reaction.
Key Terms & Definitions
- Double Displacement Reaction — Two compounds exchange ions to form two new compounds.
- Single Displacement Reaction — One element replaces another in a compound.
- Redox Reaction — Reactions involving a change in oxidation states.
- Spectator Ions — Ions not involved in the actual chemical change.
- Combustion Reaction — Hydrocarbon or alcohol reacts with oxygen, forming CO₂ and H ₂O.
- Synthesis Reaction — Two elements/compounds combine to form a single product.
- Decomposition Reaction — One compound breaks down into two or more simpler substances.
Action Items / Next Steps
- Memorize gas-forming double displacement products (H₂CO₃, H₂SO₃, NH₄OH) and their decomposition products.
- Practice predicting products and balancing reactions for all discussed reaction types.
- Review solubility rules and activity series for single displacement predictions.
- Know common oxidation states for redox reaction identification.