Class 7 Science Chapter 5 NCERT Book - Changes Around Us: Physical and Chemical

 Page 1


Changes Around Us: 
Physical and Chemical
5
I placed a cube of ice 
here half an hour ago. 
It has now become 
water!
The bottle containing 
cold water is not cold 
anymore.
The bottle containing 
cold water is not cold 
anymore.
A bud that I saw 
yesterday on this rose 
plant has become a 
? ower today.
A bud that I saw 
yesterday on this rose 
plant has become a 
? ower today.
Yesterday, I saw some 
brown spots on a 
banana, but today it 
has more brown spots 
and a strong smell.
brown spots on a 
banana, but today it 
These students are describing some changes. What kinds of 
changes are they talking about?
Chapter 5.indd   57 4/3/2025   4:52:45 PM
Page 2


Changes Around Us: 
Physical and Chemical
5
I placed a cube of ice 
here half an hour ago. 
It has now become 
water!
The bottle containing 
cold water is not cold 
anymore.
The bottle containing 
cold water is not cold 
anymore.
A bud that I saw 
yesterday on this rose 
plant has become a 
? ower today.
A bud that I saw 
yesterday on this rose 
plant has become a 
? ower today.
Yesterday, I saw some 
brown spots on a 
banana, but today it 
has more brown spots 
and a strong smell.
brown spots on a 
banana, but today it 
These students are describing some changes. What kinds of 
changes are they talking about?
Chapter 5.indd   57 4/3/2025   4:52:45 PM
Curiosity | Textbook of Science | Grade 7
58
Activity 5.1: Let us think and re? ect
You might have observed various changes happening around 
you. Some of them are listed in Table 5.1, you may notice that 
something is changing in each case. Take a moment to re? ect on 
the changes in each case. Record your observations in Table 5.1.
Table 5.1: Some changes observed around us
Making popcorn from corn 4.
5.
6.
7.
Cutting a piece of paper
Adding beetroot extract to water
Burning wood  
Drying wet clothes 8.
9.
10.
11.
Making small balls of dough 
Rolling small balls of dough into chapatis
Any other
Observation(s)
Melting ice cubes 1.
2.
3.
Chopping vegetables 
Boiling water
Change S.No.
You might have noticed that these changes could be in the size, 
shape, smell, or other property of the substance or object. Can you 
think of some other changes that happen in your surroundings? 
Make a list of those changes too.  
We observe the changes occurring around us with the help of 
our senses of sight, smell, touch, hearing, and taste.
Can we arrange these 
changes into categories?
Let us try to answer this question.
Chapter 5.indd   58 4/3/2025   4:52:45 PM
Page 3


Changes Around Us: 
Physical and Chemical
5
I placed a cube of ice 
here half an hour ago. 
It has now become 
water!
The bottle containing 
cold water is not cold 
anymore.
The bottle containing 
cold water is not cold 
anymore.
A bud that I saw 
yesterday on this rose 
plant has become a 
? ower today.
A bud that I saw 
yesterday on this rose 
plant has become a 
? ower today.
Yesterday, I saw some 
brown spots on a 
banana, but today it 
has more brown spots 
and a strong smell.
brown spots on a 
banana, but today it 
These students are describing some changes. What kinds of 
changes are they talking about?
Chapter 5.indd   57 4/3/2025   4:52:45 PM
Curiosity | Textbook of Science | Grade 7
58
Activity 5.1: Let us think and re? ect
You might have observed various changes happening around 
you. Some of them are listed in Table 5.1, you may notice that 
something is changing in each case. Take a moment to re? ect on 
the changes in each case. Record your observations in Table 5.1.
Table 5.1: Some changes observed around us
Making popcorn from corn 4.
5.
6.
7.
Cutting a piece of paper
Adding beetroot extract to water
Burning wood  
Drying wet clothes 8.
9.
10.
11.
Making small balls of dough 
Rolling small balls of dough into chapatis
Any other
Observation(s)
Melting ice cubes 1.
2.
3.
Chopping vegetables 
Boiling water
Change S.No.
You might have noticed that these changes could be in the size, 
shape, smell, or other property of the substance or object. Can you 
think of some other changes that happen in your surroundings? 
Make a list of those changes too.  
We observe the changes occurring around us with the help of 
our senses of sight, smell, touch, hearing, and taste.
Can we arrange these 
changes into categories?
Let us try to answer this question.
Chapter 5.indd   58 4/3/2025   4:52:45 PM
 Changes Around Us: Physical and Chemical
59
5.1 A Substance May Change in 
Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same!
Activity 5.2: Let us create and discuss
A. Creating some objects with paper 
? Take a few sheets of paper 
and fold them to create 
new objects (Fig. 5.1).
? Do you get the same paper 
back when you unfold 
these objects?
B. Playing with a balloon
? Take a balloon and in? ate 
it. Now, loosen your grip 
and let the air escape out.
? Do you get the unin? ated balloon back? 
? Take another balloon; in? ate it and grip the opening 
tightly. Now, prick it with a pin. 
Caution?— Be careful while using a pin.
? What happens? Will you be able to get the unin? ated 
balloon back?
C. Crushing a piece of chalk
? Crush a small piece of chalk into powder.
? Can you get the chalk piece back from the powder?
Is there any similarity in the changes listed in A, B, and C?
During all these changes, materials, such as the paper, the 
rubber sheet of the balloon, and the chalk, remained the same, 
though their appearances (shape or size) may have changed. You 
may also recall from the Grade 6 Science textbook Curiosity that 
water can exist in di? erent states (solid, liquid, and gas), and can 
change from one state to another. 
In all these cases, although we observe a change in the 
appearance, no new substance is formed. Such changes in which 
only physical properties like shape, size, and state of substances 
change are called physical changes. 
Let us explore a di? erent type of change.
Fig. 5.1: Objects made from paper
Chapter 5.indd   59 4/3/2025   4:52:46 PM
Page 4


Changes Around Us: 
Physical and Chemical
5
I placed a cube of ice 
here half an hour ago. 
It has now become 
water!
The bottle containing 
cold water is not cold 
anymore.
The bottle containing 
cold water is not cold 
anymore.
A bud that I saw 
yesterday on this rose 
plant has become a 
? ower today.
A bud that I saw 
yesterday on this rose 
plant has become a 
? ower today.
Yesterday, I saw some 
brown spots on a 
banana, but today it 
has more brown spots 
and a strong smell.
brown spots on a 
banana, but today it 
These students are describing some changes. What kinds of 
changes are they talking about?
Chapter 5.indd   57 4/3/2025   4:52:45 PM
Curiosity | Textbook of Science | Grade 7
58
Activity 5.1: Let us think and re? ect
You might have observed various changes happening around 
you. Some of them are listed in Table 5.1, you may notice that 
something is changing in each case. Take a moment to re? ect on 
the changes in each case. Record your observations in Table 5.1.
Table 5.1: Some changes observed around us
Making popcorn from corn 4.
5.
6.
7.
Cutting a piece of paper
Adding beetroot extract to water
Burning wood  
Drying wet clothes 8.
9.
10.
11.
Making small balls of dough 
Rolling small balls of dough into chapatis
Any other
Observation(s)
Melting ice cubes 1.
2.
3.
Chopping vegetables 
Boiling water
Change S.No.
You might have noticed that these changes could be in the size, 
shape, smell, or other property of the substance or object. Can you 
think of some other changes that happen in your surroundings? 
Make a list of those changes too.  
We observe the changes occurring around us with the help of 
our senses of sight, smell, touch, hearing, and taste.
Can we arrange these 
changes into categories?
Let us try to answer this question.
Chapter 5.indd   58 4/3/2025   4:52:45 PM
 Changes Around Us: Physical and Chemical
59
5.1 A Substance May Change in 
Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same!
Activity 5.2: Let us create and discuss
A. Creating some objects with paper 
? Take a few sheets of paper 
and fold them to create 
new objects (Fig. 5.1).
? Do you get the same paper 
back when you unfold 
these objects?
B. Playing with a balloon
? Take a balloon and in? ate 
it. Now, loosen your grip 
and let the air escape out.
? Do you get the unin? ated balloon back? 
? Take another balloon; in? ate it and grip the opening 
tightly. Now, prick it with a pin. 
Caution?— Be careful while using a pin.
? What happens? Will you be able to get the unin? ated 
balloon back?
C. Crushing a piece of chalk
? Crush a small piece of chalk into powder.
? Can you get the chalk piece back from the powder?
Is there any similarity in the changes listed in A, B, and C?
During all these changes, materials, such as the paper, the 
rubber sheet of the balloon, and the chalk, remained the same, 
though their appearances (shape or size) may have changed. You 
may also recall from the Grade 6 Science textbook Curiosity that 
water can exist in di? erent states (solid, liquid, and gas), and can 
change from one state to another. 
In all these cases, although we observe a change in the 
appearance, no new substance is formed. Such changes in which 
only physical properties like shape, size, and state of substances 
change are called physical changes. 
Let us explore a di? erent type of change.
Fig. 5.1: Objects made from paper
Chapter 5.indd   59 4/3/2025   4:52:46 PM
Curiosity | Textbook of Science | Grade 7
60
5.2 A Substance May Change in 
Appearance and Not Remain 
the Same!
Activity 5.3: Let us explore 
? Take two glass tumblers or small transparent bottles. Mark 
them A and B. 
? Fill one-fourth of glass tumbler A with tap water and 
one-fourth of glass tumbler B with lime water. 
? Now, blow air (exhale) into each glass tumbler, one at a time, 
using separate straws (Fig. 5.2) and observe them. 
Caution?— Do not suck the water or lime water while doing this.
Straw Straw
(a)
A B
(b)
Glass tumbler  
containing tap 
water
Glass tumbler 
containing 
lime water
Fig. 5.2: Blowing air in (a) tap water; (b) lime water
Do you notice any changes?  
In glass tumbler A, blowing air into water creates bubbles 
only, and there is no change in the appearance of the water. In 
glass tumbler B, blowing air into lime water creates bubbles, and 
turns the lime water milky (or cloudy). If we leave it for some 
time, a white substance settles at the bottom of the glass tumbler, 
indicating something new has formed. Such changes, in which 
one or more new substances are formed, are called chemical 
changes. New substances are formed through a process called 
chemical reaction. In this case, carbon dioxide from the air you 
breathe out (exhale) reacts with lime water, and forms a new 
white-coloured substance (calcium carbonate) that is insoluble 
in water. Therefore, the liquid in the bottle appears milky. Along 
with this a small amount of water is also formed. This formation 
of a new substance indicates a chemical change. The chemical 
reaction involved in this change can be represented in short 
form as a chemical equation. 
Chapter 5.indd   60 4/3/2025   4:52:47 PM
Page 5


Changes Around Us: 
Physical and Chemical
5
I placed a cube of ice 
here half an hour ago. 
It has now become 
water!
The bottle containing 
cold water is not cold 
anymore.
The bottle containing 
cold water is not cold 
anymore.
A bud that I saw 
yesterday on this rose 
plant has become a 
? ower today.
A bud that I saw 
yesterday on this rose 
plant has become a 
? ower today.
Yesterday, I saw some 
brown spots on a 
banana, but today it 
has more brown spots 
and a strong smell.
brown spots on a 
banana, but today it 
These students are describing some changes. What kinds of 
changes are they talking about?
Chapter 5.indd   57 4/3/2025   4:52:45 PM
Curiosity | Textbook of Science | Grade 7
58
Activity 5.1: Let us think and re? ect
You might have observed various changes happening around 
you. Some of them are listed in Table 5.1, you may notice that 
something is changing in each case. Take a moment to re? ect on 
the changes in each case. Record your observations in Table 5.1.
Table 5.1: Some changes observed around us
Making popcorn from corn 4.
5.
6.
7.
Cutting a piece of paper
Adding beetroot extract to water
Burning wood  
Drying wet clothes 8.
9.
10.
11.
Making small balls of dough 
Rolling small balls of dough into chapatis
Any other
Observation(s)
Melting ice cubes 1.
2.
3.
Chopping vegetables 
Boiling water
Change S.No.
You might have noticed that these changes could be in the size, 
shape, smell, or other property of the substance or object. Can you 
think of some other changes that happen in your surroundings? 
Make a list of those changes too.  
We observe the changes occurring around us with the help of 
our senses of sight, smell, touch, hearing, and taste.
Can we arrange these 
changes into categories?
Let us try to answer this question.
Chapter 5.indd   58 4/3/2025   4:52:45 PM
 Changes Around Us: Physical and Chemical
59
5.1 A Substance May Change in 
Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same! Appearance but Remain the Same!
Activity 5.2: Let us create and discuss
A. Creating some objects with paper 
? Take a few sheets of paper 
and fold them to create 
new objects (Fig. 5.1).
? Do you get the same paper 
back when you unfold 
these objects?
B. Playing with a balloon
? Take a balloon and in? ate 
it. Now, loosen your grip 
and let the air escape out.
? Do you get the unin? ated balloon back? 
? Take another balloon; in? ate it and grip the opening 
tightly. Now, prick it with a pin. 
Caution?— Be careful while using a pin.
? What happens? Will you be able to get the unin? ated 
balloon back?
C. Crushing a piece of chalk
? Crush a small piece of chalk into powder.
? Can you get the chalk piece back from the powder?
Is there any similarity in the changes listed in A, B, and C?
During all these changes, materials, such as the paper, the 
rubber sheet of the balloon, and the chalk, remained the same, 
though their appearances (shape or size) may have changed. You 
may also recall from the Grade 6 Science textbook Curiosity that 
water can exist in di? erent states (solid, liquid, and gas), and can 
change from one state to another. 
In all these cases, although we observe a change in the 
appearance, no new substance is formed. Such changes in which 
only physical properties like shape, size, and state of substances 
change are called physical changes. 
Let us explore a di? erent type of change.
Fig. 5.1: Objects made from paper
Chapter 5.indd   59 4/3/2025   4:52:46 PM
Curiosity | Textbook of Science | Grade 7
60
5.2 A Substance May Change in 
Appearance and Not Remain 
the Same!
Activity 5.3: Let us explore 
? Take two glass tumblers or small transparent bottles. Mark 
them A and B. 
? Fill one-fourth of glass tumbler A with tap water and 
one-fourth of glass tumbler B with lime water. 
? Now, blow air (exhale) into each glass tumbler, one at a time, 
using separate straws (Fig. 5.2) and observe them. 
Caution?— Do not suck the water or lime water while doing this.
Straw Straw
(a)
A B
(b)
Glass tumbler  
containing tap 
water
Glass tumbler 
containing 
lime water
Fig. 5.2: Blowing air in (a) tap water; (b) lime water
Do you notice any changes?  
In glass tumbler A, blowing air into water creates bubbles 
only, and there is no change in the appearance of the water. In 
glass tumbler B, blowing air into lime water creates bubbles, and 
turns the lime water milky (or cloudy). If we leave it for some 
time, a white substance settles at the bottom of the glass tumbler, 
indicating something new has formed. Such changes, in which 
one or more new substances are formed, are called chemical 
changes. New substances are formed through a process called 
chemical reaction. In this case, carbon dioxide from the air you 
breathe out (exhale) reacts with lime water, and forms a new 
white-coloured substance (calcium carbonate) that is insoluble 
in water. Therefore, the liquid in the bottle appears milky. Along 
with this a small amount of water is also formed. This formation 
of a new substance indicates a chemical change. The chemical 
reaction involved in this change can be represented in short 
form as a chemical equation. 
Chapter 5.indd   60 4/3/2025   4:52:47 PM
 Changes Around Us: Physical and Chemical
61
Calcium hydroxide + Carbon dioxide  Calcium carbonate + Water
       (Lime water) (Insoluble substance)
The turning of lime water milky is also used as a test for 
carbon dioxide. Let us explore this with another activity using 
some substances from our kitchen.
Activity 5.4: Let us experiment 
? Take a teaspoonful of vinegar or lemon juice in a test tube.
? Add a pinch of baking soda (sodium hydrogen carbonate) 
to it.
? What do you observe?
? You would hear a ? zzing bubbling sound and see the gas 
bubbles forming.
? Pass this gas through freshly prepared lime water kept in 
another test tube, as shown in Fig. 5.3a. 
? What do you observe?
? The lime water turns milky. What do you infer about the gas 
formed by mixing vinegar and baking soda?
This indicates that the gas formed is carbon dioxide.
This activity can also be performed using two small used 
bottles instead of test tubes and a ? exible straw, as shown in 
Fig. 5.3b.
Fig. 5.3: Reaction of vinegar and baking soda
Bubbles of 
carbon dioxide gas
Lime water
Vinegar and 
baking soda
(a) (b)
carbon dioxide gas
Since a new substance, carbon dioxide, is formed in this 
reaction, we say that a chemical change has occurred here as 
well. It can be represented as—
Vinegar + Baking soda  Carbon dioxide + Other substances
Repeat the above activity using baking soda and water. Do you 
observe any bubble formation? Is this a physical or a chemical 
change?
Chapter 5.indd   61 4/3/2025   4:52:48 PM