🔬 Chapter 5 — Changes Around Us: Physical and Chemical
Class 7 Science | Curiosity | EduGrown Notes
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🔄 Changes Around Us — Physical and Chemical! Science is everywhere!
🔄 Physical Changes
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🔄Physical Change = Only the physical properties (shape, size, state) change — NO new substance is formed!
↩️These changes are usually reversible — can be undone!
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🔄 Physical changes — shape changes but substance stays same!
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🧊 Ice melting to water — classic physical change!
✅ Examples of Physical Changes
🧊Ice melting to water (change of state)
✂️Cutting paper into pieces
🎈Inflating/deflating a balloon
🧇Chopping vegetables
🌊Water boiling to steam
📜Folding paper into origami
⚗️ Chemical Changes
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⚗️Chemical Change = NEW substance(s) are formed — original substance is changed completely!
🔥Usually irreversible — cannot easily be undone
🧪A chemical change involves a chemical reaction — atoms rearrange to form new substances
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🔥 Burning wood — irreversible chemical change, new ash formed!
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🧪 Blowing CO2 into lime water — chemical change!
⚗️ Examples of Chemical Changes
🔥Burning wood → ash + CO2 + water vapour
🌿Photosynthesis — CO2 + water → glucose + O2
🍳Cooking food — proteins denature, new flavours form
🧪CO2 + lime water → calcium carbonate (turns milky!)
🌧️Iron rusting — iron + oxygen + water → iron oxide (rust)
🍌Ripening of fruit — starch converts to sugar
🔍 Signs of a Chemical Change
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🌡️Change in temperature (heat released or absorbed)
🌈Change in colour
💨Production of a gas (bubbles, fizzing)
🏔️Formation of a precipitate (solid settling in liquid)
👃Change in smell (new odour produced)
💡Emission of light or sound
💡 How to Remember the Difference?
🔄 Physical: Physical properties change, Product is still the same substance, usually Reversible
⚗️ Chemical: New substance formed, Not easily reversible, involves a Reaction!
Remember: Tearing paper = physical | Burning paper = chemical!
⚗️ Chemical: New substance formed, Not easily reversible, involves a Reaction!
Remember: Tearing paper = physical | Burning paper = chemical!
⭐ Quick Summary
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📝 Key Points
🔄Physical change: shape/size/state changes, NO new substance, usually reversible (cutting, melting)
⚗️Chemical change: NEW substance formed, usually irreversible (burning, rusting, cooking)
🔍Signs of chemical change: colour change, gas production, precipitate, temperature change, new smell