Extra 30 short questions and answers from the Chapter:6 Changes Around Us for Class 6 CBSE Science:-
What are reversible changes? Give an example.
Ans:
A reversible change is a change that can be undone or reversed to get back the original substance. Example: Melting of ice.
What are irreversible changes? Give an example.
Ans:
An irreversible change is a change that cannot be reversed, and a new substance is formed. Example: Burning of paper.
Define physical change with an example.
Ans:
A physical change is a change where no new substance is formed, and the original substance retains its properties. Example: Tearing of paper.
Define chemical change with an example.
Ans:
A chemical change is a change where a new substance is formed with different properties. Example: Rusting of iron.
Give two examples of reversible changes.
Ans:
(
i
) Melting of ice, (ii) Boiling of water.
Give two examples of irreversible changes.
Ans:
(
i
) Cooking of food, (ii) Burning of wood.
What happens when water is heated?
Ans:
When water is heated, it changes into steam due to
evaporation
, which is a
reversible
change.
What happens when water is cooled?
Ans:
When water is cooled, it turns into ice due to
freezing
, which is a
reversible
change.
Why is cooking food an irreversible change?
Ans:
Cooking food is an irreversible change because new substances with different properties are formed, and we cannot get the raw ingredients back.
Is rusting of iron a chemical change? Why?
Ans:
Yes, rusting of iron is a chemical change because a new substance (iron oxide) is formed, and the change is irreversible.
Why does a metal expand on heating?
Ans:
When heated, metal particles move faster and take up more space, causing the metal to expand.
What happens when a stretched rubber band is released?
Ans:
The rubber band returns to its original shape, showing a
reversible change
.
What type of change occurs when milk is turned into curd?
Ans:
It is an
irreversible chemical change
because curd cannot be changed back into milk.
Why does a balloon burst when too much air is blown into it?
Ans:
When air is blown, the balloon expands, and if the pressure is too high, it bursts. This is an
irreversible change
.
What is contraction? Give an example.
Ans:
Contraction is the decrease in size of an object when cooled. Example: A metal ring shrinks when cooled.
What happens when butter is heated?
Ans:
Butter melts and turns into liquid, which is a
reversible change
because it can solidify again on cooling.
Give an example of a slow change and a fast change.
Ans:
(
i
)
Slow change:
Rusting of iron.
(ii)
Fast change:
Bursting of a cracker.
How is cutting paper different from burning paper?
Ans:
Cutting paper is a
physical change
(reversible), whereas burning paper is a
chemical change
(irreversible).
Why is growing of a plant an irreversible change?
Ans:
A plant cannot be changed back into a seed, and new substances are formed, making it an
irreversible change
.
What kind of change is melting of wax and burning of wax?
Ans:
Melting of wax is a
physical reversible change
, while burning of wax is a
chemical irreversible change
.
What type of change occurs when a lump of dough is rolled into chapati?
Ans:
Rolling dough into a chapati is a
physical change
as it can be changed back, but baking the chapati is an
irreversible chemical change
.
What type of change occurs when a metal is bent?
Ans:
Bending a metal is a
physical change
because no new substance is formed.
How can we prove that boiling water is a reversible change?
Ans:
When water is boiled, it turns into steam. If the steam is cooled, it turns back into water, proving it is
reversible
.
What happens when sugar is dissolved in water? Is it a reversible change?
Ans:
Sugar dissolves completely in water, forming a solution. It is
reversible
as sugar can be recovered by
evaporation
.
Why does rusting occur faster in coastal areas?
Ans:
Rusting occurs faster in coastal areas due to the presence of moisture and salt in the air, which speeds up the oxidation process.
What is an example of a periodic change?
Ans:
The
rising and setting of the Sun
is a periodic change because it happens regularly.
Why does iron expand when heated?
Ans:
When heated, the molecules of iron move apart, causing the metal to expand.
Which type of change is the germination of a seed?
Ans:
Germination of a seed is an
irreversible chemical change
as a new plant is formed.
Why is tearing of paper a physical change?
Ans:
Tearing of paper is a physical change because no new substance is formed, but the shape of the paper changes.
Why does a candle become smaller when it burns?
Ans:
When a candle burns, wax is converted into gases and smoke, which cannot be changed back. This makes it an
irreversible chemical change
.
