Chemical Reactions
Chemistry · रासायनिक अभिक्रियाएं
📋Quick Overview
A chemical reaction is a process where reactants are transformed into products with different chemical properties. Signs of a chemical reaction include: change in colour, evolution of gas, change in temperature, formation of precipitate, or change in state. Chemical equations must be balanced — same number of atoms on both sides (Law of Conservation of Mass by Lavoisier).
📖Types of Chemical Reactions
| Type | Description | General Form | Example |
|---|---|---|---|
| Combination (Synthesis) | Two or more substances combine to form one product | A + B → AB | 2Mg + O₂ → 2MgO (burning magnesium) |
| Decomposition | One substance breaks into two or more | AB → A + B | 2H₂O → 2H₂ + O₂ (electrolysis of water) |
| Displacement (Single) | More reactive element replaces less reactive | A + BC → AC + B | Zn + CuSO₄ → ZnSO₄ + Cu |
| Double Displacement | Exchange of ions between two compounds | AB + CD → AD + CB | NaCl + AgNO₃ → AgCl↓ + NaNO₃ |
| Redox | Oxidation and reduction happen simultaneously | Oxidation + Reduction | CuO + H₂ → Cu + H₂O |
📖Oxidation vs Reduction
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Remember: OIL RIG — Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). The substance that gets oxidized is the Reducing Agent. The substance that gets reduced is the Oxidizing Agent.
📖Exothermic vs Endothermic Reactions
📖Types of Decomposition
- •Thermal Decomposition — by heat. Example: CaCO₃ → CaO + CO₂ (limestone to quicklime)
- •Electrolytic Decomposition — by electricity. Example: 2H₂O → 2H₂ + O₂ (electrolysis of water)
- •Photolytic Decomposition — by light. Example: 2AgCl → 2Ag + Cl₂ (silver chloride in sunlight turns grey)
📖Everyday Examples of Reactions
- •Rusting of iron: 4Fe + 3O₂ + water → 2Fe₂O₃·xH₂O (slow oxidation, needs moisture)
- •Corrosion: When metals react with air/water/acids and get damaged (rusting is corrosion of iron)
- •Rancidity: When fats/oils get oxidized, food smells bad. Prevented by adding antioxidants or nitrogen packing.
- •Galvanization: Coating iron with zinc to prevent rusting
- •Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (endothermic, uses sunlight)