Chemical Reactions & Acids/Bases
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Chemistry Decoder: The Magic of Change
Phase 1: The Foundation (Physical vs Chemical)
Not all changes are permanent. If you can "Undo" it, it's usually physical. If it's "Forever", it's usually chemical.
| Feature | Physical Change | Chemical Change |
|---|---|---|
| Definition | Only form/state changes. | New substance is formed. |
| Reversibility | Reversible (usually). | Irreversible (usually). |
| Examples | Melting ice, Cutting paper. | Rusting iron, Curdling milk. |
Phase 2: The Core Logic (Acids & Bases)
1. The pH Scale (Strength Meter)
Think of the pH scale (0 to 14) as a balance. 7 is The Neutral Center (Water).
- Acids (0 to 6): Sour taste, turns Blue Litmus Red. (Ex: Lemon, Stomach acid).
- Bases (8 to 14): Bitter taste, soapy feel, turns Red Litmus Blue. (Ex: Soap, Baking soda).
2. Types of Reactions
| Type | Concept | Example |
|---|---|---|
| Exothermic | Releases Heat (Gets hot). | Burning wood, Respiration. |
| Endothermic | Absorbs Heat (Gets cold). | Photosynthesis, Melting ice. |
| Neutralization | Acid + Base $ | |
| ightarrow$ Salt + Water. | Antacid for acidity. |
Phase 3: The Exam Edge (Redox & Corrosion)
1. Oxidation & Reduction (Redox)
- Oxidation: Gaining Oxygen or Losing Electrons.
- Reduction: Losing Oxygen or Gaining Electrons.
2. Everyday Corrosion
- Rusting of Iron: Needs both Air (Oxygen) and Moisture. It is a chemical change.
- Galvanization: Coating iron with Zinc to prevent rusting.
- Rancidity: When oil/fats in food get oxidized and smell bad. (Nitrogen gas in chips packets prevents this).
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