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Understanding the Name of the Chapter
The chapter is called "Changes Around Us: Physical and Chemical" .
Let us break it down:
CHANGES
Alters appearance, state, or composition
PHYSICAL
Same substance · New look
CHEMICAL
New substance formed · Different properties
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Changes
Anything that alters the appearance, state, or composition of a substance — ice melting, a balloon bursting, a banana ripening. -
Physical
A change that affects only the appearance — size, shape, or state — and no new substance is formed . -
Chemical
A change in which one or more new substances are formed . Often the new substance has a different colour, smell, or property.
In this chapter, we will learn about different physical and chemical changes happening around us.
Topics We Will Study in This Chapter
Topics We Will Study
5.1
A Substance May Change in Appearance but Remain the Same!
5.2
A Substance May Change in Appearance and Not Remain the Same!
5.3
Some Other Processes Involving Chemical Changes
5.4
Can Physical and Chemical Changes Occur in the Same Process?
5.5
Are Changes Permanent?
5.6
Are All Changes Desirable?
5.7
Some Slow Natural Changes
Activity 5.1 — Spot the Changes Around You
The chapter opens with a reflection activity:
Procedure
- Look at each change listed in Table 5.1.
- Note what is changing — size, shape, smell, colour, state, or something else.
- Record your observations in the table.
Table 5.1 — Some Changes Observed Around Us
| S.No. | Change | Observation(s) |
|---|---|---|
| 1. | Melting ice cubes | Solid ice becomes liquid water; shape lost; same substance — can be refrozen. |
| 2. | Chopping vegetables | One whole becomes many small pieces; size and shape change; same substance. |
| 3. | Boiling water | Water (liquid) turns into steam (gas); bubbles seen; can be condensed back. |
| 4. | Making popcorn from corn | Hard kernels become soft, fluffy puffs; size, shape, smell all change; cannot reverse. |
| 5. | Cutting a piece of paper | One sheet becomes many smaller pieces; same paper material; cannot become whole again. |
| 6. | Adding beetroot extract to water | Clear water turns pinkish-red; only colour mixes; no new substance formed. |
| 7. | Burning wood | Wood becomes ash and smoke; new substances; heat and light produced; cannot reverse. |
| 8. | Drying wet clothes | Water evaporates from cloth; cloth becomes dry; can re-wet. |
| 9. | Making small balls of dough | Flat dough becomes round balls; only shape changes; same dough. |
| 10. | Rolling balls of dough into chapatis | Round balls become flat circles; only shape changes; same dough. |
| 11. | Mixing salt in water | Salt disappears into water; water tastes salty; salt can be recovered by evaporation. |
Observation
- The changes you record can be in size, shape, smell, colour, state, taste, or some other property of the substance or object.
- For some changes (1, 3, 5, 8, 9, 10, 11) you can clearly recognise the same substance after the change — just looking different.
- For other changes (4, 7, and a ripening fruit) the substance itself seems to have turned into something new (popcorn from corn; ash and smoke from wood).
- Many changes can be reversed (1, 3, 8, 9, 10, 11); a few cannot (4, 5, 7).
Explanation
- We notice these changes using our five senses — sight, smell, touch, hearing, and taste.
- Once we have a list of changes, the next step is to arrange them into categories .
- The simplest grouping is: changes where no new substance is formed (physical) versus changes where a new substance IS formed (chemical).
- The rest of this chapter develops this grouping carefully and shows how to tell the two apart.
We use our senses — sight, smell, touch, hearing, and taste — to notice these changes. The next question is: can we sort them into categories?
