๐ Class 7 Science Curiosity – Chapter 5 Notes
๐ Changes Around Us: Physical and Chemical | Amresh Academy
๐ Introduction
- Physical Changes
- Chemical Changes
⚙️ 1. Types of Changes
๐น Physical Changes
๐ Change in:
- Shape
- Size
- State
❌ No new substance is formed
๐ Examples:
- ❄️ Melting ice
- ๐ Folding paper
- ๐ง Boiling water
- ๐ Inflating a balloon
๐น Chemical Changes
๐ New substance is formed through a chemical reaction ๐งช
๐ Examples:
- ๐ฅ Burning wood
- ๐งฑ Rusting iron
- ๐งช Vinegar + baking soda
- ๐ฅ Curdling milk
๐ง 2. Characteristics
⚪ Physical Changes:
- No new substance
- Often reversible
๐ด Chemical Changes:
- New substances formed
- Usually irreversible
๐งช 3. Key Examples
๐น Physical Changes:
- ❄️ Melting ice cubes
- ๐ฅ Cutting vegetables
- ๐ Drying clothes
๐น Chemical Changes:
๐งฑ Rusting:
๐ Iron + Oxygen → Iron oxide
๐ฅ Combustion:
๐งช Lime Water Test:
๐ CO₂ + Lime water → Calcium carbonate (milky)
๐ฅ 4. Combustion
๐ A chemical reaction with oxygen
⚡ Requirements:
- ๐ฅ Fuel
- ๐ฌ️ Oxygen
- ๐ก️ Ignition temperature
๐ฏ️ Example:
๐ Burning candle:
- Wax melting → Physical change
- Wax burning → Chemical change
๐ 5. Reversible vs Irreversible Changes
✔️ Reversible Changes:
๐ Can be reversed
- Ice ↔ Water
- Water ↔ Steam
❌ Irreversible Changes:
๐ Cannot be reversed
- Burning wood
- Making popcorn
๐ฏ 6. Desirable vs Undesirable Changes
✔️ Desirable Changes:
๐ Useful changes
- Cooking food ๐ฒ
- Ripening fruits ๐
❌ Undesirable Changes:
๐ Harmful changes
- Rusting ๐งฑ
- Food spoilage ๐
⚠️ Note:
๐ 7. Natural Changes
๐ชจ Weathering:
๐ Formation of soil
- Physical → Breaking rocks
- Chemical → Rusting in rocks
๐ Erosion:
๐ Movement of soil
- Caused by wind ๐ฌ️
- Or water ๐ง
๐ Final Summary
๐ Changes around us are of two main types:
- Physical → No new substance
- Chemical → New substance formed
๐ Understanding changes helps us in:
- Daily life
- Industry
- Environment ๐
✨ Perfect for revision + exams + quick understanding ๐
