In this Class 7 Science Curiosity Chapter 5 Changes Around Us Physical and Chemical, we will explore the different types of changes – physical and chemical – and understand how they affect substances. Some changes may only affect the appearance, while others form entirely new substances.
We will also learn about reversible and irreversible changes, desirable and undesirable changes, and how natural forces like wind and water slowly break down rocks over time.
Changes Around Us Physical and Chemical
We see many changes happening around us every day. Ice melts into water, paper burns to ash, milk turns into curd, and fruits ripen. But have you ever wondered – why do these changes happen, are they permanent, or can we get the original material back?
Through simple observations and activities, this chapter helps us understand:
- How to identify physical and chemical changes.
- What conditions are needed for combustion.
- Why some changes are useful and others are harmful.
- How nature slowly shapes the Earth through weathering and erosion.
This chapter builds a strong foundation for understanding changes in materials, both in our everyday life and in the natural world.
Also download:
Class 7 Science Worksheet Curiosity
Class 7th Science NCERT Solutions Curiosity
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Physical and Chemical Changes Notes
Physical Changes
- Only physical properties like shape, size, and state change.
- No new substance is formed.
- Examples: Melting ice, cutting paper, folding cloth.
Chemical Changes
- New substances with different properties are formed.
- Involve chemical reactions.
- Examples: Rusting iron, burning wood, curdling milk.
Some Important Chemical Changes
- Rusting: Iron + Water + Oxygen → Rust (iron oxide)
- Combustion: Magnesium + Oxygen → Magnesium oxide + Heat + Light
Physical and Chemical Change Together
- Example: Burning a candle:
- Melting of wax – Physical change
- Burning of wax vapour – Chemical change
Reversible and Irreversible Changes
- Reversible: Can be undone. (e.g., melting wax)
- Irreversible: Cannot be undone. (e.g., curdling milk)
Desirable and Undesirable Changes
- Desirable: Cooking, digestion, composting.
- Undesirable: Rusting, food spoilage.
Natural Changes
- Weathering: Physical and chemical breakdown of rocks.
- Erosion: Transport of sediments by wind or water.
Changes Around Us Class 7 Questions and Answers
Q1. What is a physical change?
Ans: A change in which no new substance is formed and only the appearance or state changes.
Q2. What is a chemical change?
Ans: A change in which one or more new substances are formed with different properties.
Q3. Define ignition temperature.
Ans: The lowest temperature at which a substance catches fire.
Q4. Name a natural process that includes both physical and chemical changes.
Ans: Weathering of rocks.
Q5. Why is burning a candle both physical and chemical?
Ans: Wax melts (physical), vapour burns (chemical).
Q6. Why is rusting of iron a chemical change?
Ans: Rusting of iron is a chemical change because a new substance, iron oxide (rust), is formed that cannot be converted back into iron.
Class 7 Science Curiosity Chapter 5 MCQs
Q1. Which of the following is a chemical change?
a) Boiling water
b) Melting wax
c) Rusting
d) Freezing water
Q2. The burning of magnesium ribbon produces:
a) Carbon dioxide
b) Water
c) Magnesium oxide
d) None of these
Q3. What turns lime water milky?
a) Carbon dioxide
b) Oxygen
c) Hydrogen
d) Nitrogen