Living Science Chemistry Class 6 ICSE Solutions Chapter 5 Changes Around Us

ICSE Living Science Chemistry for Class 6 Solutions Chapter 5 Changes Around Us

Check Your Progress

Answer these questions.
Question 1.
Tick the type of change that occurs in the following cases.
a. Growth of a tree (natural/man-made)
Answer:
natural

b. Evaporation of water from a lake (slow/fast)
Answer:
slow

c. Erosion of soil (desirable/undesirable)
Answer:
undesirable

d. Change of day and night (periodic/non-periodic)
Answer:
periodic

Question 2.
Are the following changes reversible or irreversible ?
a. Ripening of fruits
Answer:
irreversible

b. Dissolving of sugar in water
Answer:
Reversible

c. Glowing of an electric bulb
Answer:
Reversible

d. Burning of a piece of paper
Answer:
Irreversible

A. Tick the most appropriate answer.

Question 1.
Which of the following is not an example of a natural change ?
a. Change of day and night
b. Change of seasons
c. Eruption of a volcano
d Cooking food
Answer:
d. Cooking food

Question 2.
Cutting down of trees in an example of
a. a desirable change
b. an undesirable change
c. cannot say
d none of these
Answer:
c. cannot say

Question 3.
Which of the following is not a reversible change ?
a. Stretching of a rubber band
b. Dissolving sugar in water
c. Burning of magnesium in air
d Evaporation of water
Answer:
c. Burning of magnesium in air

Question 4.
Which of the following is not a physical change ?
a. Drying of wet clothes
b. Sublimation
c. Melting of wax
d Rusting of iron
Answer:
d. Rusting of iron

Question 5.
Physical changes are
a. permanent
b. periodic
c. temporary
d irreversible
Answer:
c. temporary

B. Tick the correct words.

Question 1.
The eruption of a volcano is a (fast/man-made) change.
Answer:
fast

Question 2.
A cyclone is (a periodic/undesirable) change.
Answer:
an undesirable

Question 3.
Germination of seeds is an (undesirable/irreversible) change.
Answer:
irreversible

Question 4.
Phases of the moon is a (periodic/man-made) change.
Answer:
periodic

Question 5.
Heating of sugar is a (chemical/physical) change.
Answer:
chemical

C. State if the following statements are true or false. Correct the statement if it is false.

Question 1.
The occurrence of tide is a man-made change.
Answer:
False. The occurrence of tide is a natural change.

Question 2.
Burning of magnesium ribbon is an irreversible change.
Answer:
True

Question 3.
Boiling of water is a physical change.
Answer:
True

Question 4.
Magnetization of iron is a chemical change.
Answer:
False. Magnetization of iron is a physical change.

Question 5.
Burning of a candle involves both physical and chemical changes.
Answer:
True

D. Name the following.

Question 1.
A type of change that is made by humans
Answer:
Man-made change

Question 2.
A type of change that occurs within a very short period of time
Answer:
Fast change

Question 3.
A type of change that is useful to us
Answer:
Desirable change

Question 4.
A type of change that is repreated at regular intervals of time
Answer:
Periodic change

Question 5.
A type of change that can be returned to its original form by reversing the conditions.
Answer:
Reversible change

E. State whether the following are physical changes.

Question 1.
Drying of wet clothes
Answer:
Physical

Question 2.
Formation of curd from milk
Answer:
Chemical

Question 3.
Photosynthesis
Answer:
Chemical

Question 4.
Burning of wood
Answer:
Chemical

Question 5.
Dissolving sugar in water
Answer:
Physical

Question 6.
Bursting of a fire cracker
Answer:
Chemical

Question 7.
Cooking of food
Answer:
Chemical

Question 8.
Glowing of an electric lamp
Answer:
Physical

Question 9.
Rusting of iron
Answer:
Chemical

F. Answer the following in detail.

Question 1.
Differentiate between the following changes with suitable examples.
a. Natural and man-made changes
Answer:
Natural:

1. These are changes that occur in nature on their own.
2. We have no control over
3. Examples : Change of day and night, earthquakes, growth of living beings, volcano etc

Man-made changes :

1. These are changes that occur due to the efforts or activities of humans.
2. We can control these changes. changes.
3. Examples: Burning of fuels, cooking of food,cutting of trees, etc.

b. Slow and fast changes
Answer:
Slow :

1. Changes that occur over a long period of time (few hours or many years) are called slow changes.
2. Examples : Rusting of iron, germination of seed, tooth decay, soil formation, freezing of water, etc.

Fast changes :

1. Changes that occur within a very short period of time or within seconds are called fast changes.
2. Examples : Burning of paper lightning, during a thunderstorm, occurrence of earthquakes, etc.

c. Periodic and non-periodic changes
Answer:
Periodic

1. These are changes that are repeated at regular intervals of time.
2. Examples – Change of seasons, high tides and low tides, heartbeat, swinging of a clock pendulum, etc.

Non-periodic changes :

1. These are changes that may occur at any time or occur irregularly.
2. Examples: Dust storm, rainfall, earthquakes, landslides, etc.

d. Desirable and undesirable changes Ans.
Desirable

1. These are changes that are useful to human beings.
2. Examples : Cooking of food, ripening of fruits, change of season, formation of curd from milk, etc.

Undesirable changes :

1. These are changes that are harmful to us or cause destruction.
2. Examples: Cyclone, spoilage of food, curdling of milk, soil erosion, rusing of iron, etc.

e. Reversible and irreversible changes.
Answer:
Reversible

1. These are changes that can be reversed (returned to its original form) by reversing the conditions.
2. Examples : Melting of ice, evaporation of water, glowing of an electric bulb, dissolving sugar in water, etc.

Irreversible changes :

1. These are changes that cannot be reversed.
2. Examples : Cooking of food, Rusting of iron, burning of paper, curdling of milk, etc.

Question 2.
Define a physical change and a chemical change. Give two examples of each.
Answer:
A physical change is a change in which no new substance is formed. It is temporary and usually reversible. Examples : Drying of wet clothes, stretching a rubber band, glowing of an electric bulb, etc. A chemical change is a permanent change in which the original substance loses its own composition and properties and forms a new substance. Examples : Cooking of food, digestion of food, rusting of iron, burning of paper, etc.

Question 3.
Give two differences between a physical change and a chemical change.
Answer:

Question 4.
Explain why the burning of a candle is an example of both physical as well as chemical changes.
Answer:
Burning of a candle involves physical as well as chemical changes –
1. During the burning of a candle, some wax melts and solidifies back to wax on cooling. Therefore, this shows that melting of wax is a physical change.

2. During burning of a candle, some wax undergoes combustion. It bums to produce new substances : carbon dioxide and water vapour. Therefore, this also shows a chemical change.

Question 5.
Give two reasons to explain whether the following are physical or chemical changes.
a. Burning of wood
Answer:
Burning of wood is a chemical change as when wood is burnt in air, they undergo changes to form carbon dioxide and water vapour (new substances). The change is permanent and irreversible as ash cannot be converted back to wood.

b. Melting of ice
Answer:
Melting of ice is a physical change as it is temporary and reversible. Ice can be formed again by freezing water. No new substance is formed. The chemical composition of water does not change.

c. Glowing of an electric bulb
Answer:
Glowing of an electric bulb is a physical change as it is reversible and no new substance is formed inside the bulb. When an electric bulb is switched on, electric current passes through the filament of the bulb and the filament glows to give light. When switched off, the filament returns to its normal condition and the bulb stops glowing.

d. Cooking of food
Answer:
Cooking of food is a chemical change because the composition of raw grains and vegetables changes and new substances are formed. It is not possible to get the raw vegetables from cooked food. This shows that the change is permanent and irreversible.

e. Rusting of iron
Answer:
Rusting of iron is a chemical change as the composition and properties of rust are different from those of iron. Rust cannot be converted back to iron by simple physical methods. Therefore, the change is irreversible and permanent.

G. Give reasons for the following.

Question 1.
The processes of boiling and evaporation are physical changes.
Answer:
Process of boiling and evaporation involves the change of state from liquid to gaseous. Only the physical state of substance changes. Chemical composition of the substance does not change. No new substance is formed and this process can be reversed by condensation.

Question 2.
During a chemical change new substances are formed.
Answer:
The original substances undergo changes to form new substances which have composition and properties different from the original substances. These new substances cannot be converted back to the original substances.

Living Science Chemistry Class 6 ICSE Solutions