🔹 1. Chemical Reaction
- A chemical reaction involves transformation of reactants into products.
- It involves breaking and forming of chemical bonds.
- Signs of a chemical reaction:
- Change in state
- Change in color
- Evolution of gas
- Change in temperature
- Formation of precipitate
🔹 2. Chemical Equation
- Representation of a chemical reaction using symbols and formulas.
- Word equation: Magnesium + Oxygen → Magnesium oxide
- Chemical equation: Mg + O₂ → MgO
🔹 3. Balanced and Unbalanced Equations
- Balanced equation: Equal number of atoms of each element on both sides.
- Unbalanced equation: Unequal number of atoms.
- Balanced using Law of Conservation of Mass: Mass can neither be created nor destroyed.
🔹 4. Types of Chemical Reactions
- Combination Reaction
- Two or more substances combine to form a single product.
- Example: CaO + H₂O → Ca(OH)₂
- Decomposition Reaction
- A compound breaks down into simpler substances.
- Example: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
- Displacement Reaction
- A more reactive element displaces a less reactive element.
- Example: Zn + CuSO₄ → ZnSO₄ + Cu
- Double Displacement Reaction
- Exchange of ions between two compounds.
- Example: Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
- Redox Reaction
- Involves both oxidation and reduction.
- Example: CuO + H₂ → Cu + H₂O
🔹 5. Oxidation and Reduction
- Oxidation: Gain of oxygen or loss of hydrogen.
- Reduction: Loss of oxygen or gain of hydrogen.
- Redox = Oxidation + Reduction
🔹 6. Effects of Oxidation in Daily Life
- Corrosion
- Iron reacts with oxygen and moisture → rust (Fe₂O₃·xH₂O)
- Prevention: Painting, greasing, galvanizin
- Rancidity
- Oxidation of fats/oils causes bad smell/taste
- Prevention: Refrigeration, antioxidants, air-tight packaging
🔹 7. Important Terms
- Reactants: Substances that react
- Products: Substances formed
- Exothermic Reaction: Releases heat
- Endothermic Reaction: Absorbs heat
- Precipitate: Insoluble solid formed in a solution