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

Students can use Class 7 Science Curiosity Extra Questions and Chapter 5 Changes Around Us Physical and Chemical Extra Question Answer to prepare effectively at home.

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.
Write of change is physical or chemical.
(a) Cutting of wood
(b) Beat aluminium to make foil
(c) Milk change into curd
(d) Sediment formation
Answer:
(a) Physical change
(b) Physical change
(c) Chemical change
(d) Physical change

Question 2.
Name chemical present in vinegar.
Answer:
Acetic Acid.

Question 3.
Baking soda is mixed to lemon juice, bubbles are formed with formation of a gas. Name the gas.
Answer:
Carbon dioxide.

Question 4.
What type of change is called in which new substance with new properties is formed?
Answer:
Chemical change

Question 5.
Combustion, cooking, and rusting are chemical changes, justify the statement.
Answer:
In all these processes, new substances are being formed.

Question 6.
Give two examples of a chemical change.
Answer:
(i) Rusting of iron (ii) Curdling of milk

Question 7.
What is the colour of flame when magnesium ribbon is burnt?
Answer:
White colour

Question 8.
During rusting, which new substance is formed?
Answer:
Iron oxide

Question 9.
Define ignition temperature.
Answer:
The minimum temperature of a substance at which it catches fire is called its ignition temperature.

Question 10.
When baking soda is mixed with vinegar then a gas is released. Name the gas.
Answer:
Carbon dioxide

Question 11.
What is the colour of rust?
Answer:
Reddish brown colour

Question 12.
Gives examples of natural slow changes.
Answer:
Weathering of rocks and erosion

Question 13.
Name two desirable changes.
Answer:
Formation of curd or paneer from milk, decomposition of food waste into compost.

Question 14.
When water is frozen, ice is formed. Ice has different properties. Why do we call it a physical change ?
Answer:
Because no new substance is formed.

Question 15.
Name a process where physical and chemical changes occur.
Answer:
Burning of a candle.

Changes Around Us Physical and Chemical Class 7 Short Question Answer

Question 1.
Give one example of irreversible change.
Answer:
Rusting of iron.

Question 2.
Write an example of chemical change in following:
(a) Evolution of gas
(b) Evolution of heat
Answer:
(a) Vinegar is mixed to baking soda.
(b) Magnesium is burnt in air.

Question 3.
Name any three combustible substances.
Answer:
(a) Cotton, (b) Wood, (c) Kerosene oil.

Question 4.
What are three requirements of combustion?
Answer:
(a) Heat (permit a fuel to reach ignition temperature)
(b) Oxygen and
(c) Fuel

Question 5.
The ice melts, but we can refreeze it into ice. What type of change is it?
Answer:
It is a physical change that can be reversed too.

Question 6.
Name two changes in rocks to make soil.
Answer:
(a) Physical change and
(b) Chemical change

Question 7.
Give the chemical reaction for the burning of magnesium.
Answer:
Magnesium + Oxygen ⟶ Magnesium Oxide + Light + Heat↑

Question 8.
Why does lime water turn milky if O₂ is passed through it?
Answer:
Lime water + CO₂ ⟶ It turns milky.
Lime water + Carbon dioxide ⟶ Calcium Carboneate + Water

Question 9.
What are physical properties?
Answer:
The properties such as shape, size, colour, and state of a substance that can be observed are called physical properties.

Question 10.
What are physical changes?
Answer:
The changes in which a substance undergoes a change in its physical properties are called physical changes.
Physical changes are generally reversible. In such changes, no new substances are formed. For example, melting of ice, formation of steam, etc.

Question 11.
What is chemical change?
Answer:
A change in which one or more new substances are formed is called a chemical change. A chemical change is caused by a chemical reaction. For example, formation of curd from milk, burning of paper, etc.

Question 12.
Define rusting. How can it be prevented?
Answer:
Rust formation on iron is called Rusting. It can be prevented by oiling, painting, greasing etc.

Question 13.
Some changes observed around us are as follows:
Burning of wood, Boiling of water, Freezing of water, burning of a candle, water added to beetroot extract.
Select Reverse and Irreversible changes.
Answer:

Reversible changes	Irreversible changes
1. Boiling of water	1. Burning of wood
2. Freezing of water	2. Burning of candle

Question 14.
Explain how water can exist in solid, liquid, and gas forms.
Answer:
Water exists in three states. When heated, water becomes gas; when frozen, water becomes ice (solid); ice melts to liquid water.

Question 15.
Distinguish between a physical and a chemical change.
Answer:
Difference between physical and chemical changes:

A Physical change	A Chemical change
1. Only change in appearance. No new substances is formed.	1. New substance formed.
2. e.g., chalk converted into powder.	2. e.g., candle burns to make vapours and wax.
3. Reversible change	3. Reversible change.

Question 16.
What is combustion? Name any combustible substance. What are three requirements of combustion?
Answer:
(a) Combustion is “a chemical reaction in which a substance reacts to oxygen and heat is produced along with a new substance.”
(b) Kerosene is a combustible substance.
(c) It needs fuel, oxygen, and heat.

Question 17.
What do you know about a scientist named Michael Faraday?
Answer:
He delivered a series of lectures. He stated that a candle was perfect object for scientific studies. He made some important contributions in various fields of science. He discussed physical as well as chemical processes. Various processes such as combustion and melting was discussed by him in the nineteenth century at all.

Question 18.
How would you explain candle burning in terms of physical and chemical changes?
Answer:
A candle burns. The wax melts. Vapours are formed. Wax vapours produce a flame. This includes solidification and evaporation. Both are physical changes. Burning of the vapours is chemical change. We can conclude that candle burning is a physical and a chemical change at all.

Question 19.
Enlist five chemical changes. (V. Imp.)
Answer:
(a) Rusting of iron, (b) formation of a new substance when magnesium is burnt in air, (c) burning of a candle, (d) water is added in beetroot extract and (e) burning of magnesium.

Question 20.
What does burning of a candle show?
Answer:
(a) Wax of candle melts, (b) is carried up the wick, (c) and evaporates due to heat, (d) vapour of wax burns and produces flame.
All of these are physical changes at all. On the contrary, the burning a vapour is a chemical change.
Conclusion: Both physical and chemical changes occur during burning of a candle.

Question 21.
A substance may change in appearance but not remain same. Justity. (V. Imp.)
Answer:
Blow air into water. It creates bubbles only. There is no change in water. When you blow air in the lime water; it creates bubbles. The air changes colour as it becomes milky or even cloudy. After some time, a white substance is formed. It shows that a new substance is formed. It is a chemical change.

Question 22.
Analyse the chemical equation given below:
Lime water + Carbon dioxide → Calcium Carbonate + Water.
Answer:
Carbon dioxide reacts will lime water and forms a new substance named calcium hydroxide. But it is not soluble in water. It is a chemical change formed by a chemical reaction at all. Calcium Carbonate is insoluble in water.

Changes Around Us Physical and Chemical Class 7 Long Question Answer

Question 1.
Are all changes permanent? Explain by citing example. (M. Imp.)
Answer:
When a thing undergoes change, it can return to an original form. It means changes can be reversed e.g., the ice melts; and it can be frozen into ice also. Another example is that water evaporates; may be condensed back into liquid water also. But certain changes cannot be reversed like chopped vegetables do not come to its original shape and size. Other example is of popcorn – making it cannot go back to its shape at all.
So there are two types of change (a) one that is reversed, (b) another cannot be reversed i.e., irreversible.

Question 2.
Explain weathering of rocks. (M. Imp.)
Answer:
Weathering is the process by which rocks are broken down into smaller pieces, eventually forming soil. It occurs through both physical and chemical changes. Physical weathering occurs when large rocks break into smaller pieces without changing their chemical composition. This can be caused by change in temperature due to climate, the growth of tree roots, or the freezing of water within cracks in the rocks. Chemical weathering happens when water or chemicals in the water react with the minerals in rocks, changing their composition. For example, a black coloured rock called basalt, which contains iron, undergoes a chemical change. When exposed to water or moist air for a long time, the iron reacts with oxygen to form iron oxide, which gives the rock a red colour.

Question 3.
How would you prove that oxygen is necessary for combustion? (V. Imp.)
Answer:
Aim: Lets find out whether the presence of oxygen is essential for combustion.

Material Required: One glass tumbler, two identical candles, two petridishes etc.

Procedure:

1. Place two candles on two separate petridishes, light them with matchbox.
2. Cover one of the candles with a glass tumbler.
3. Record your observations.

Observations:

1. The candle that was not covered as in Fig. (a) continues to burn.
2. The covered candle as in Fig. (b) stops burning after some time.

Inference
Oxygen from the air is essential for combustion. If you cover a burning candle, it cannot get air and the flame goes out because there is no oxygen to support burning. You can test the carbon dioxide gas by adding a small amount of lime water in the petridish. You will notice that it turns milky due to the formation of calcium carbonate. This confirms that oxygen is required for combustion.

Changes Around Us Physical and Chemical Class 7 Case Based Questions

1. Read the following passage carefully and answer the questions that follow:
The sediments lie at the base of mountains. They are formed by physical changes. These changes break big rocks into smaller ones. Several causes of it are climatic, temperature conditions, water freezing in cracks of the rocks as well as roots of plants which are growing there. All these cause breaking of the rocks. Chemical present in water react to rocks and change their composition also. This is called a physical change.

(i) How are physical changes in rocks caused?
(a) Temperature changes
(b) Tree roots are growing in rocks
(c) The freezing water found there
(d) All of these
Answer:
(d) All of these

(ii) How are rocks formed?
(a) Sediments lie at base of mountains
(b) Physical change take place in them
(c) Both (a) and (b)
(d) None of these
Answer:
(c) Both (a) and (b)

(iii) Does any chemical change occur there?
(a) Chemical in water react to rocks
(b) Changed rock composition
(c) Its cause is water or chemicals in it
(d) All of these
Answer:
(d) All of these

(iv) How are rocks formed?
Answer:
Rocks are formed by physical and chemical changes in sediments. The big rocks break into smaller ones. Some factors affect this as temperature, chemicals of water etc.

2. Read the following passage carefully and answer the questions that follow:
The Case of the Melting Ice and Inflated Balloons
During a group discussion, students shared everyday changes they had observed-ice cubes melting, paper being folded, and balloons inflating or bursting. Their teacher explained that these are all examples of physical changes, which may alter the size, shape, or state of matter, but do not produce new substances. They also discussed reversible and irreversible changes.

(i) When ice melts into water, what type of change occurs?
(a) Physical and reversible
(b) Physical and irreversible
(c) Chemical and reversible
(d) Chemical and irreversible
Answer:
(a) Physical and reversible

(ii) Bursting of an inflated balloon is:
(a) A reversible physical change
(b) An irreversible physical change
(c) A chemical change
(d) None of these
Answer:
(b) An irreversible physical change

(iii) Folding paper into different shapes (like origami) is classified as:
(a) Physical and irreversible
(b) Chemical and irreversible
(c) Physical and reversible
(d) Chemical and reversible
Answer:
(c) Physical and reversible

(iv) What is a common feature of all physical changes?
(a) Formation of a new substance
(b) Permanent colour change
(c) Only physical properties like shape or state change
(d) Emission of light
Answer:
(c) Only physical properties like shape or state change

Changes Around Us Physical and Chemical Class 7 Picture Based Questions

1. Look at the picture and answer the following questions:

(i) What does the above given Fig. (a) show?
(a) Focusing sunrays using a magnifying glass
(b) Focusing light to ignite paper
(c) Light passing through a magnifying glass
(d) None of these
Answer:
(a) Focusing sunrays using a magnifying glass

(ii) What does Fig. (b) show?
(a) Making a hole through paper
(b) Paper catches fire
(c) Sunrays heat up the paper
(d) None of these
Answer:
(b) Paper catches fire

(iii) What is called ignition temperature?
Answer:
Focusing sunrays on the paper heats it. The temperature of the paper increases with time. After some time, the paper becomes so hot that it starts burning. This minimum temperature at which a substance catches fire is called its ignition temperature.

2. Look at the picture and answer the following questions:

(i) What does this figure show?
(a) Action of an acid over sodium carbonate
(b) Action of sodium carbonate on acid
(c) Release of gas
(d) None of these
Answer:
(a) Action of an acid over sodium carbonate

(ii) Name the gas released.
(a) Oxygen
(b) Hydrogen
(c) Carbon dioxide
(d) Nitrogen
Answer:
(c) Carbon dioxide

(iii) How is lime water affected?
Answer:
The lime water becomes milky.

Changes Around Us Physical and Chemical Extra Questions for Practice

Multiple Choice Questions (MCQs)

Question 1.
Select the correct option:
(a) Vinegar + Baking soda ⟶ Carbon dioxide + Other substances
(b) Vinegar +O₂ ⟶ CO₂+ Other substances
(c) Vinegar + Iron ⟶ Carbon dioxide + Other substances
(d) None of these

Question 2.
Which one is correct?
(a) A cube of ice melts
(b) A rose plant grows to form a flower
(c) On a banana, brown spots develop after five days
(d) All of these

Question 3.
Select the physical change:
(a) A piece of paper is folded to create new objects
(b) A chark crushed to make powder
(c) Ice cubes melt
(d) All of these

Question 4.
A candle burns:
(a) It is a physical change
(b) It is a chemical change
(c) Both (a) and (b)
(d) None of these

Very Short Answer Type Questions:

Question 1.
Write two examples of reversible changes.

Question 2.
Explain the process of rust formation of iron.

Question 3.
How would you test for carbon dioxide gas formed after burning of a candle?

Question 4.
Write two combustible substances.

Short Answer Type Questions:

Question 1.
What is needed to start combustion?

Question 2.
What changes occur when a candle is lit?

Question 3.
Write the events when a candle burns.

Question 4.
Mention two changes that can be reversed and two changes that cannot be reversed.

Question 5.
Write about the weathering of rocks.

Question 6.
How is soil formed?

Question 7.
In a nutshell, briefly explain erosion.

Question 8.
Some changes are desirable while some are not. Explain with examples.

Long Answer Type Questions:

Question 1.
Is air is essential for combustion? Explain with the help of an activity.

Question 2.
Explain weathering of rocks.

Question 3.
Which gas is released when vinegar and baking soda are mixed? What happens when this gas is passed through lime water?