1. Chemical Reaction
A chemical reaction is a process in which one or more substances change into new substances with different properties.
Signs of a Chemical Reaction
- ✅ Change in colour
- ✅ Evolution of gas
- ✅ Change in temperature
- ✅ Formation of precipitate
- ✅ Change in state
2. Chemical Equation
Example:
Magnesium + Oxygen → Magnesium Oxide
Balanced equation:
2Mg + O₂ → 2MgO
Why Balance Chemical Equations?
- Follows the Law of Conservation of Mass
- Number of atoms on both sides must be equal.
3. Types of Chemical Reactions
(A) Combination Reaction
Two or more substances combine to form one product.
Example:
CaO + H₂O → Ca(OH)₂
(B) Decomposition Reaction
One compound breaks into simpler substances.
Example:
2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
(C) Displacement Reaction
A more reactive element displaces a less reactive element.
Example:
Zn + CuSO₄ → ZnSO₄ + Cu
(D) Double Displacement Reaction
Exchange of ions between two compounds.
Example:
AgNO₃ + NaCl → AgCl↓ + NaNO₃
AgCl is a white precipitate.
(E) Oxidation and Reduction (Redox)
Oxidation:
- Addition of oxygen
- Removal of hydrogen
Reduction:
- Removal of oxygen
- Addition of hydrogen
Example:
CuO + H₂ → Cu + H₂O
- CuO is reduced
- H₂ is oxidized
4. Oxidation in Everyday Life
Corrosion
Slow destruction of metals due to air and moisture.
Example:
Rusting of iron.
Prevention:
- Painting
- Oiling/Greasing
- Galvanization
- Electroplating
Rancidity
Oxidation of oils and fats causing bad smell and taste.
Prevention:
- Store in airtight containers
- Refrigeration
- Add antioxidants
- Nitrogen flushing in food packets
Important Definitions
- Reactants: Substances that take part in a reaction.
- Products: New substances formed.
- Precipitate: Insoluble solid formed during a reaction.
- Catalyst: Increases reaction speed without being consumed.
Most Important Chemical Equations (Learn These)
- 2Mg + O₂ → 2MgO
- CaO + H₂O → Ca(OH)₂
- Zn + H₂SO₄ → ZnSO₄ + H₂↑
- Zn + CuSO₄ → ZnSO₄ + Cu
- Fe + CuSO₄ → FeSO₄ + Cu
- AgNO₃ + NaCl → AgCl↓ + NaNO₃
- CuO + H₂ → Cu + H₂O
- 2H₂ + O₂ → 2H₂O
- 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
- 2Fe + O₂ + H₂O → Fe₂O₃·xH₂O (Rust)