Changes Around Us Physical and Chemical Class 7 Extra Questions and Answers Science Chapter 5

By tackling these Class 7 Science Extra Questions and Class 7 Curiosity Chapter 5 Extra Question Answer Changes Around Us Physical and Chemical, students will build a solid foundation in the topic.

Class 7 Science Chapter 5 Changes Around Us Physical and Chemical Extra Questions

Class 7 Science Chapter 5 Extra Questions on Changes Around Us Physical and Chemical

Changes Around Us Physical and Chemical Class 7 Very Short Question Answer

Question 1.
What is the change called in which physical properties of substance changes?
Answer:
Physical change

Question 2.
Which are the three essential factors for combustion?
Answer:
Combustible substance, oxygen and ignition temperature.

Question 3.
Burning candle is which kind of change?
Answer:
Both physical and chemical changes.

Question 4.
Which kind of change is rusting?
Answer:
It is a chemical change.

Question 5.
Why the balloon inflated when yeast is pourd in bottle filled with sugar solution?
Answer:
Because yeast forms carbon dioxide by decomposing sugar, that is why balloon inflated.

Question 6.
What is ignition temperature?
Answer:
That minimum temperature on which a substance starts burning.

Question 7.
What is weathering?
Answer:
Breaking of rocks is called weathering.

Question 8.
What is the name of the phenomena by which firefly shines?
Answer:
Bioluminescence

Question 9.
Name a desirable change which is also irreversible.
Answer:
Making chapatis with the flour.

Question 10.
Which is reversible change—melting of ice or changing milk in curd?
Answer:
Melting ice is reversible change.

Question 11.
Write an example of desirable change.
Answer:
Stitching clothes.

Question 12.
What is irreversible change?
Answer:
Changes which cannot get back are called irreversible changes.

Question 13.
Which substance is formed when magnesium ribbon bums?
Answer:
Magnesium oxide is formed.

Question 14.
By which process soil is formed in nature?
Answer:
By the process of weathering.

Question 15.
How did a chemical change indicated?
Answer:
By chemical reactions.

Changes Around Us Physical and Chemical Class 7 Short Question Answer

Question 1.
Write differences in physical and chemical changes.
Answer:
Physical properties of matter are changed in physical changes, e.g. formation of . powder by chalk, no new substance is formed. Whereas in chemical changes, a new substance is formed, e.g. changing milk into curd.

Question 2.
What is combustion?
Answer:
Combustion is a chemical change in which a substance reacts with oxygen and form heat and light is called combustion the substance which bums are known as combustible substance like paper, wood, cotton, kerosene etc.

Question 3.
Define ignition temperature.
Answer:
Ignition temperature is the minimum temperature on which any substance catches fire. Ex. : Burning matchstick have temperature more than ignition temperature of paper so paper catches fire immediately.

Question 4.
Write difference in reversible and irreversible changes.
Answer:
Action of any substance is started at a point and getting it back in its original state is reversible change and some changes cannot be reversed back are called irreversible change.

Question 5.
How human is responsible for atmospheric pollution?
Answer:
The increased consumption of fuel in cars, trains, aeroplanes etc. are increasing the amount of C0₂ in atmosphere, drying of paint on walls, doors etc. releases substance by evaporation caused atmospheric pollution.

Question 6.
What is called Bioluminescense?
Answer:
Bioluminescence is a chemical reaction in which light is produced without heat. It is also called wonder of nature eg. firefly insect which is seen in fields and gardens in evening. Their lighting is a chemical change.

Question 7.
Write differences in desirable and undesirable changes.
Answer:
Some changes in daily life are useful and fulfill our needs known as desirable change e.g. changing milk into curd, ripening of fruits etc. In contrast, some changes are harmful for us in any form are called undesirable e g. rusting of iron. Question 8. Describe change when a candle burns. Answer: Melting of wax when a candle bums is a physical change and burning of wax vapour is a chemical change. Melting wax and vapourising is irreversible and solidifying of wax is a reversible change. So it is both physical and chemical changes.

Changes Around Us Physical and Chemical Class 7 Long Question Answer

Question 1.
How to identify chemical change. Explain with an example.
Answer:
Changes in which one or more new substances are formed, are called chemical changes e g. blowing in lime water, turns the lime water milky, if it is left untouched for some time then a white substance settles at the bottom, which exhibit formation of a new subtance chemical reaction

Question 2.
What are the essential conditions for combustion. Explain.
Answer:
For combustion, combustible substance, oxygen and ignition temperature (on which temperature, substance starts to bum) are essential. Fuel is a combustible substance, oxygen reacts and temperature should be adequate to burn substance. Light and heat both are produced in combustion.

Question 3.
Write difference in physical and chemical changes with example.
Answer:
Only physical properties are changed in physical change. Ex. : Melting of ice, folding of paper, breaking of rocks etc. No new substance formed. New substance formed in chemical change. Ex.: Making of curd, combustion, rusting in iron. Physical changes can be reversible but chemical reactions are mostly irreversible.

Question 4.
How does soil formed in nature?
Answer:
Formation of soil in nature is happen because of weathering. Rocks broken in pieces with temperature, rain and air etc. which is a physical change. These rocks dissolves by chemical reactions. Broken particles of rocks form soil by chemical changes. This process happen in 0 thousands years and important for fertility of soil. Thus rocks form soil by both chemical and physical changes.

Question 5.
Describe chemical and physical changes when a candle burns.
Answer:
Both changes can be seen when a candle bums. First, wax melts and liquid is formed which is a physical change. Then this liquid wax pulled upward with the help of a wick and form wax vapour by vapourising. Wax vapour bums by . reacting with oxygen and produce C02, vapour, heat and light which is a chemical change. So burning of candle is an example of both physical and chemical changes

Wax + O₂ → CO₂ + H₂O + Heat + Light

Question 6.
Explain differences in reversible and irreversible changes with example.

Reversible change	Irreversible change
1. After change in any substancc, getting it back in same state is called reversible change.	I After change. if substance does not get back in same state is called irreersjbIe change.
2. Only state of matter change.	2. A new substance formed by changing the original
3. Mainly physical changes.	3. Changes arc main Ichetnical.
4. Ex. Melting of ice and so1idif back as ice.	4. Ex. Making of curd by milk (but milk cannot get back by curd)

Question 7.
How does chemical changes are identified? Explain with an experiment in which gas is released and also write chemical reaction.
Answer:
Chemical changes are identified with formation of new substance, colour change, gas emission and with production of heat or light.

Experiment : Take a test tube, mix vinegar (an acid) with baking soda (a base). Bubbles of CO₂ gas are released in this reaction. This gas can be identified by passing through lime water, which turned milky.

Chemical reaction :

This reaction is clearly a chemical change, because new’ substance (salt and gas) are formed.

Question 8.
What is combustion? Describe process of burning of magnesium ribbon with its chemical reaction. Make a diagram also.
Answer:
Combustion is a chemical reaction in which a substance reacts fastly with oxygen and produce heat and light.
Combustion of magnesium: When magnesium ribbon is heated in flame. It bums with white shiny

Question 9.
Explain the chemial reaction of rusting in iron. Also write the factors responsible for it.
Answer:
Metals spoiled after coming in contact with moisture, oxygen and acids of atmosphere. Rusting in iron is most common example of it.

Chemical reaction :
Iron forms iron oxide by reaction in presence of oxygen and water, known as rust.

Factors responsible for rusting:

1. Presence of moisture
2. Oxygen in air
3. Salt : Rusting is fast when object comes in contact with sea shore and salt water.
4. Presence of acids : Acidic atmosphere enhances corrosion.