🌟 Class 7 Science Curiosity – Chapter 5 Notes
🔄 Changes Around Us: Physical and Chemical | Amresh Academy
📘 Introduction
- Physical Changes
- Chemical Changes
⚙️ 1. Types of Changes
🔹 Physical Changes
👉 Change in:
- Shape
- Size
- State
❌ No new substance is formed
📌 Examples:
- ❄️ Melting ice
- 📄 Folding paper
- 💧 Boiling water
- 🎈 Inflating a balloon
🔹 Chemical Changes
👉 New substance is formed through a chemical reaction 🧪
📌 Examples:
- 🔥 Burning wood
- 🧱 Rusting iron
- 🧪 Vinegar + baking soda
- 🥛 Curdling milk
🧠 2. Characteristics
⚪ Physical Changes:
- No new substance
- Often reversible
🔴 Chemical Changes:
- New substances formed
- Usually irreversible
🧪 3. Key Examples
🔹 Physical Changes:
- ❄️ Melting ice cubes
- 🥕 Cutting vegetables
- 👕 Drying clothes
🔹 Chemical Changes:
🧱 Rusting:
👉 Iron + Oxygen → Iron oxide
🔥 Combustion:
🧪 Lime Water Test:
👉 CO₂ + Lime water → Calcium carbonate (milky)
🔥 4. Combustion
👉 A chemical reaction with oxygen
⚡ Requirements:
- 🔥 Fuel
- 🌬️ Oxygen
- 🌡️ Ignition temperature
🕯️ Example:
👉 Burning candle:
- Wax melting → Physical change
- Wax burning → Chemical change
🔁 5. Reversible vs Irreversible Changes
✔️ Reversible Changes:
👉 Can be reversed
- Ice ↔ Water
- Water ↔ Steam
❌ Irreversible Changes:
👉 Cannot be reversed
- Burning wood
- Making popcorn
🎯 6. Desirable vs Undesirable Changes
✔️ Desirable Changes:
👉 Useful changes
- Cooking food 🍲
- Ripening fruits 🍎
❌ Undesirable Changes:
👉 Harmful changes
- Rusting 🧱
- Food spoilage 🍞
⚠️ Note:
🌍 7. Natural Changes
🪨 Weathering:
👉 Formation of soil
- Physical → Breaking rocks
- Chemical → Rusting in rocks
🌊 Erosion:
👉 Movement of soil
- Caused by wind 🌬️
- Or water 💧
📌 Final Summary
👉 Changes around us are of two main types:
- Physical → No new substance
- Chemical → New substance formed
👉 Understanding changes helps us in:
- Daily life
- Industry
- Environment 🌍
✨ Perfect for revision + exams + quick understanding 🚀
