Overview
This lecture introduces chemical reactions and equations, methods for representing and balancing them, types of chemical reactions, and the effects of oxidation in everyday life.
Introduction to Chemical Reactions
- Chemical reactions involve changes in the nature and identity of substances.
- Signs of a chemical reaction include change in state, color, temperature, and evolution of gas.
- A chemical reaction can be represented as a word equation and then as a chemical equation.
Writing and Balancing Chemical Equations
- Word equations list the reactants and products; arrows indicate direction.
- Chemical formulas in equations make them concise.
- A balanced chemical equation has equal numbers of atoms of each element on both sides.
- The law of conservation of mass requires equations to be balanced.
- Use the hit-and-trial method to balance chemical equations.
- Physical states are shown as (s) solid, (l) liquid, (g) gas, (aq) aqueous.
Types of Chemical Reactions
Combination Reactions
- Two or more substances combine to form a single product.
- Example: CaO(s) + H₂O(l) → Ca(OH)₂(aq) + heat (exothermic reaction).
Decomposition Reactions
- A single compound breaks down into two or more products.
- Types include thermal (heat), photolytic (light), and electrolytic (electricity) decomposition.
- Example: CaCO₃(s) → CaO(s) + CO₂(g) (thermal).
Displacement Reactions
- A more reactive element displaces a less reactive one from its compound.
- Example: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s).
Double Displacement Reactions
- Ions are exchanged between two compounds, often forming a precipitate.
- Example: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq).
Oxidation and Reduction (Redox Reactions)
- Oxidation is gain of oxygen or loss of hydrogen.
- Reduction is loss of oxygen or gain of hydrogen.
- Redox reactions involve simultaneous oxidation and reduction.
- Example: 2Cu + O₂ → 2CuO (oxidation); CuO + H₂ → Cu + H₂O (reduction).
Effects of Oxidation in Everyday Life
Corrosion
- Metals react with environmental substances, causing rust (iron) or tarnishing (silver, copper).
- Corrosion damages various metal objects and structures.
Rancidity
- Fats and oils oxidize, producing unpleasant smell/taste.
- Antioxidants or airtight storage prevent rancidity in foods.
Key Terms & Definitions
- Reactant — Substance that undergoes chemical change in a reaction.
- Product — New substance formed as a result of a chemical reaction.
- Balanced Chemical Equation — Equation with equal numbers of each type of atom on both sides.
- Combination Reaction — Reaction where two or more reactants form a single product.
- Decomposition Reaction — Reaction where a single compound splits into multiple products.
- Displacement Reaction — Reaction in which one element replaces another in a compound.
- Double Displacement Reaction — Reaction involving the exchange of ions between reactants.
- Oxidation — Gain of oxygen or loss of hydrogen.
- Reduction — Loss of oxygen or gain of hydrogen.
- Redox Reaction — Reaction involving both oxidation and reduction.
- Corrosion — Gradual destruction of metals due to reaction with environment.
- Rancidity — Spoilage of fats and oils due to oxidation.
Action Items / Next Steps
- Practice writing and balancing chemical equations for given reactions.
- Complete textbook exercises and group activities as assigned.
- Review examples of each reaction type and their distinguishing features.