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MATTER - Questions & Answers

TEST YOUR KNOWLEDGE 1

1. All matter is made up of very small particles called molecules.

2. The molecules of a gas have the maximum kinetic energy.

3. The intermolecular force of attraction is negligible in gases.

4. Molecules in a solid are most tightly packed.

5. The molecules of a gas are free to move in any direction.

TEST YOUR KNOWLEDGE 2

1. The change of state from solid to liquid is called melting (or fusion).

2. The change of state from liquid to gas is called vaporization (or boiling).

3. The process of change of a liquid into its vapour at any temperature below its boiling point is called evaporation.

4. The change of state from gas to liquid is called condensation.

5. The change of state from liquid to solid is called freezing (or solidification).

EXERCISES I. Multiple Choice Questions

1. The intermolecular force of attraction is maximum in:

(a) solids

2. The intermolecular space is maximum in:

(c) gases

3. The molecules can move freely anywhere in:

(c) gases

4. The kinetic energy of molecules is maximum in:

(c) gases

5. The process of change of state from solid to gas directly is called:

(c) sublimation

II. Fill in the blanks

1. The change of state from liquid to solid is called freezing.

2. The change of state from liquid to gas is called vaporization.

3. The process of change of a state from solid to liquid is called melting.

4. The process of change of a state from gas to liquid is called condensation.

5. The temperature at which a liquid changes into gas is called its boiling point.

III. Match the following

1. Solid to liquid

(e) melting

2. Liquid to gas

(c) vaporization

3. Gas to liquid

(a) condensation

4. Liquid to solid

(b) freezing

5. Solid to gas

(d) sublimation

IV. Write True or False

1. The molecules of a liquid are in constant motion.

True

2. The intermolecular force of attraction is maximum in gases.

False

3. On heating, the kinetic energy of molecules increases.

True

4. The boiling point of water is 100°C.

True

5. Evaporation takes place only at the boiling point of a liquid.

False

V. Theoretical Questions

1. Define matter.

Matter is defined as anything that has mass, occupies space and can be perceived by our senses. It is composed of tiny particles called molecules.

2. State the kinetic theory of matter.

The kinetic theory of matter states that: (i) Matter is made up of tiny particles called molecules. (ii) The molecules are in a state of continuous random motion. (iii) The molecules exert forces of attraction on each other called intermolecular forces. (iv) The space between the molecules is called intermolecular space. (v) The kinetic energy of the molecules increases with an increase in temperature.

3. Distinguish between solids, liquids and gases on the basis of their properties.

Solids: Have a definite shape and volume, molecules are closely packed, and intermolecular force is very strong. Liquids: Have a definite volume but no definite shape, molecules are less closely packed, and intermolecular force is weaker than in solids. Gases: Have neither a definite shape nor a definite volume, molecules are far apart, and intermolecular force is negligible.

4. Describe the change of state from solid to liquid using kinetic theory.

When a solid is heated, its molecules gain kinetic energy and start vibrating more vigorously. At the melting point, the molecules acquire enough energy to overcome the strong intermolecular forces of attraction. They leave their fixed positions and begin to move within the boundary of the substance, thus changing into a liquid.

5. Describe the change of state from liquid to gas using kinetic theory.

On heating a liquid, the kinetic energy of its molecules increases. At the boiling point, the molecules acquire sufficient kinetic energy to completely overcome the intermolecular forces of attraction. They become free to move in all directions and escape the liquid surface, changing into a gas.

6. What is evaporation? State three factors on which the rate of evaporation depends.

Evaporation is the process by which a liquid changes into its vapour state at any temperature below its boiling point. Three factors affecting evaporation are: (i) Surface area of the liquid, (ii) Temperature of the liquid and its surroundings, and (iii) Humidity of the air.

7. Distinguish between evaporation and boiling.

Evaporation: It is a slow process that occurs only at the surface of the liquid at all temperatures. It causes cooling. Boiling: It is a rapid process that occurs throughout the entire mass of the liquid at a specific constant temperature (boiling point). No cooling is caused.

8. What is sublimation? Give two examples of substances which sublimate.

Sublimation is the process in which a solid directly changes into its gaseous state on heating, without passing through the liquid state. Examples: Camphor and Ammonium Chloride.

9. What is deposition? Give one example.

Deposition (or solidification) is the process in which a gas directly changes into its solid state on cooling, without passing through the liquid state. Example: Formation of frost from water vapour.

10. Why does a gas exert pressure on the walls of the container?

The molecules of a gas are in a state of continuous random motion at high speeds. During their motion, they collide with each other and also with the walls of the container. These collisions of molecules on the walls exert a force per unit area, which is known as gas pressure.

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Multiple Choice Questions - Test your understanding with these MCQs. Click "Show Answer" to reveal the correct answer.

Question 1According to the kinetic theory, matter is composed of tiny particles called:

Correct Answer: Molecules

Question 2What is the approximate size of a molecule?

Correct Answer: 10^-10 metre

Question 3The empty space between molecules of matter is known as:

Correct Answer: Inter-molecular space

Question 4Which force holds the molecules of matter together?

Correct Answer: Inter-molecular force

Question 5The force of attraction between molecules of the same substance is called:

Correct Answer: Force of cohesion

Question 6The force of attraction between molecules of two different substances is called:

Correct Answer: Force of adhesion

Question 7In which state of matter are the inter-molecular forces the strongest?

Correct Answer: Solid

Question 8In which state of matter is the inter-molecular space the maximum?

Correct Answer: Gas

Question 9Molecules in a solid move by:

Correct Answer: Vibrating about their mean positions

Question 10Which Indian philosopher originally considered matter to be made of five 'tatvas'?

Correct Answer: Ancient Indian Philosophers

Question 11Maharishi Kanada called the tiny particles of matter:

Correct Answer: Anu

Question 12A molecule composed of only one atom, like Helium, is called:

Correct Answer: Monoatomic

Question 13Which of the following is an example of a diatomic molecule?

Correct Answer: Oxygen

Question 14Water (H2O) is an example of which type of molecule?

Correct Answer: Polyatomic

Question 15When sugar is dissolved in water, the water level does not rise because:

Correct Answer: Sugar particles occupy inter-molecular spaces of water

Question 16The zig-zag motion of particles suspended in a liquid or gas is known as:

Correct Answer: Brownian motion

Question 17Which experiment demonstrates the random motion of particles?

Correct Answer: Lycopodium powder on water

Question 18The inter-molecular force is effective only up to a separation of approximately:

Correct Answer: 10^-9 metre

Question 19Which state of matter has a definite shape and definite volume?

Correct Answer: Solid

Question 20Which state of matter has a definite volume but no definite shape?

Correct Answer: Liquid

Question 21Which state of matter has neither a definite shape nor a definite volume?

Correct Answer: Gas

Question 22Why do solids have a definite shape?

Correct Answer: Strong inter-molecular forces keep molecules in fixed positions

Question 23Liquids can flow because:

Correct Answer: Molecules can slide over one another

Question 24Gases fill the entire space available to them because:

Correct Answer: Inter-molecular forces are negligible

Question 25The change of a solid into a liquid on heating is called:

Correct Answer: Melting

Question 26The constant temperature at which a solid changes into a liquid is called:

Correct Answer: Melting point

Question 27The process of a liquid changing into a solid on cooling is called:

Correct Answer: Freezing

Question 28For a pure substance, the melting point and freezing point are:

Correct Answer: The same

Question 29What is the melting point of ice?

Correct Answer: 0°C

Question 30What is the boiling point of water at standard pressure?

Correct Answer: 100°C

Question 31According to the text, what is the melting point of wax?

Correct Answer: 55°C

Question 32The heat absorbed during a change of state that does not result in a temperature rise is called:

Correct Answer: Latent heat

Question 33During the melting process, the temperature of a substance:

Correct Answer: Remains constant

Question 34The change of a liquid into a gas at a fixed temperature is called:

Correct Answer: Boiling

Question 35The process of a gas changing into a liquid on cooling is called:

Correct Answer: Condensation

Question 36What happens to the kinetic energy of molecules during boiling?

Correct Answer: It is used to overcome attractive forces (potential energy increases)

Question 37Which of the following substances undergoes sublimation?

Correct Answer: Camphor

Question 38Sublimation is the process where a solid changes directly into:

Correct Answer: Vapour

Question 39The reverse process of sublimation, where a gas changes directly to a solid, is called:

Correct Answer: Deposition

Question 40Solid Carbon Dioxide is also known as:

Correct Answer: Dry ice

Question 41Which of these is a difference between evaporation and boiling?

Correct Answer: Evaporation occurs at all temperatures; boiling at a fixed point

Question 42Evaporation takes place at:

Correct Answer: The surface of the liquid

Question 43Boiling is considered a:

Correct Answer: Rapid and violent process

Question 44Which phenomenon is responsible for the cooling effect when sweat dries?

Correct Answer: Evaporation

Question 45How does an increase in the surface area of a liquid affect evaporation?

Correct Answer: It increases the rate of evaporation

Question 46How does an increase in temperature affect the rate of evaporation?

Correct Answer: Increases it

Question 47How does high humidity affect the rate of evaporation?

Correct Answer: Decreases it

Question 48Blowing air over a liquid surface increases evaporation because:

Correct Answer: It removes liquid molecules near the surface

Question 49Why are volatile liquids like alcohol kept in tightly closed bottles?

Correct Answer: To prevent rapid evaporation

Question 50The melting point of ice decreases when:

Correct Answer: Pressure increases
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True or False Questions - Determine whether each statement is true or false. Click "Show Answer" to reveal the correct answer.

Statement 1Matter is defined as anything that occupies space and has mass.

Correct Answer: True

Statement 2Sound and light are examples of matter according to the text.

Correct Answer: False

Statement 3Indian philosophers originally classified matter into five constituents called 'tatvas'.

Correct Answer: True

Statement 4Maharishi Kanada called the tiny particles of matter 'molecules'.

Correct Answer: False

Statement 5A molecule is the smallest unit of matter that can exist independently.

Correct Answer: True

Statement 6A molecule of Helium is diatomic.

Correct Answer: False

Statement 7A molecule of water is polyatomic.

Correct Answer: True

Statement 8The approximate size of a molecule is 10^-10 metres.

Correct Answer: True

Statement 9When sugar dissolves in water, the volume of water increases significantly.

Correct Answer: False

Statement 10Inter-molecular spaces are largest in solids.

Correct Answer: False

Statement 11The force of attraction between molecules of the same substance is called cohesion.

Correct Answer: True

Statement 12The force of attraction between molecules of different substances is called adhesion.

Correct Answer: True

Statement 13Brownian motion refers to the random, zig-zag motion of particles suspended in a fluid.

Correct Answer: True

Statement 14Solids have a definite shape and a definite volume.

Correct Answer: True

Statement 15Liquids have a definite shape but no definite volume.

Correct Answer: False

Statement 16Gases have neither a definite shape nor a definite volume.

Correct Answer: True

Statement 17Inter-molecular forces are strongest in gases.

Correct Answer: False

Statement 18Molecules in a solid can move freely throughout the substance.

Correct Answer: False

Statement 19Molecules in a solid vibrate about their mean positions.

Correct Answer: True

Statement 20Liquids can flow because their molecules can slide over one another.

Correct Answer: True

Statement 21Gases are highly compressible compared to solids.

Correct Answer: True

Statement 22Inter-molecular force is effective up to a separation of about 10^-9 metres.

Correct Answer: True

Statement 23The temperature of a substance rises continuously during the process of melting.

Correct Answer: False

Statement 24Melting is the change of state from solid to liquid by absorbing heat.

Correct Answer: True

Statement 25The melting point of ice is 100°C.

Correct Answer: False

Statement 26Wax melts at 55°C.

Correct Answer: True

Statement 27Freezing is the process where a liquid changes into a solid by rejecting heat.

Correct Answer: True

Statement 28For a pure substance, the melting point and freezing point are the same.

Correct Answer: True

Statement 29Water contracts when it freezes into ice.

Correct Answer: False

Statement 30Wax contracts when it freezes.

Correct Answer: True

Statement 31Increasing pressure decreases the melting point of ice.

Correct Answer: True

Statement 32Increasing pressure decreases the melting point of wax.

Correct Answer: False

Statement 33Adding salt to ice raises its melting point.

Correct Answer: False

Statement 34Latent heat causes a change in the temperature of a substance.

Correct Answer: False

Statement 35Boiling takes place at all temperatures.

Correct Answer: False

Statement 36Evaporation takes place at all temperatures.

Correct Answer: True

Statement 37The boiling point of water is 100°C.

Correct Answer: True

Statement 38Vaporization is a slow and gradual process.

Correct Answer: False

Statement 39Evaporation takes place only at the surface of the liquid.

Correct Answer: True

Statement 40Boiling occurs throughout the entire mass of the liquid.

Correct Answer: True

Statement 41Evaporation produces a heating effect.

Correct Answer: False

Statement 42Condensation is the change of state from vapour to liquid.

Correct Answer: True

Statement 43The boiling point of a liquid decreases with an increase in pressure.

Correct Answer: False

Statement 44Food cooks faster in a pressure cooker because water boils at a higher temperature.

Correct Answer: True

Statement 45At high altitudes, water boils at a temperature lower than 100°C.

Correct Answer: True

Statement 46Adding impurities to a liquid lowers its boiling point.

Correct Answer: False

Statement 47Sublimation is the process where a solid changes directly into a gas.

Correct Answer: True

Statement 48Deposition is the process where a gas changes directly into a liquid.

Correct Answer: False

Statement 49Camphor and Iodine are examples of substances that sublime.

Correct Answer: True

Statement 50Dry ice is solid water.

Correct Answer: False
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Fill in the Blanks - Complete the sentences by filling in the missing words. Click "Show Answer" to check your response.

Question 1Matter is defined as anything that occupies ______ and has mass.

Correct Answer: space

Question 2Indian philosophers considered matter to be made up of five constituents called ______.

Correct Answer: tatvas

Question 3Maharishi Kanada called the tiny particles of matter ______.

Correct Answer: anu

Question 4It is now established that matter is composed of tiny particles called ______.

Correct Answer: molecules

Question 5A molecule composed of one atom is called a ______ molecule.

Correct Answer: monoatomic

Question 6A molecule composed of two atoms, such as oxygen or hydrogen, is called a ______ molecule.

Correct Answer: diatomic

Question 7The approximate size of a molecule is ______ metre.

Correct Answer: 10^-10

Question 8The spacing between the molecules of matter is called ______ space.

Correct Answer: inter-molecular

Question 9The force of attraction between the molecules of matter is called ______ force.

Correct Answer: inter-molecular

Question 10The force of attraction between molecules of the same substance is called the force of ______.

Correct Answer: cohesion

Question 11The force of attraction between molecules of two different substances is called the force of ______.

Correct Answer: adhesion

Question 12In solids, the molecules ______ about their mean positions without leaving them.

Correct Answer: vibrate

Question 13The rapid, random, zig-zag motion of particles suspended in a liquid or gas is called ______ motion.

Correct Answer: Brownian

Question 14Inter-molecular forces are effective only up to a separation of ______ metre.

Correct Answer: 10^-9

Question 15Solids have a definite ______ and a definite volume.

Correct Answer: shape

Question 16Liquids have a definite volume but no definite ______.

Correct Answer: shape

Question 17Gases have neither a definite ______ nor a definite volume.

Correct Answer: shape

Question 18The inter-molecular force is ______ in solids.

Correct Answer: strongest

Question 19The inter-molecular space is ______ in gases.

Correct Answer: maximum

Question 20In liquids, molecules can move freely within the ______ of the liquid.

Correct Answer: boundary

Question 21Gases are highly ______ due to the large spaces between their molecules.

Correct Answer: compressible

Question 22Liquids and gases can flow because the molecular forces of attraction in them are ______.

Correct Answer: weak

Question 23The process of change from one state to another at a constant temperature is called change of ______.

Correct Answer: state

Question 24Change of solid into liquid on heating is called ______ or fusion.

Correct Answer: melting

Question 25The fixed temperature at which a solid changes into a liquid is called the ______ point.

Correct Answer: melting

Question 26Change of liquid into solid on cooling is called ______.

Correct Answer: freezing

Question 27The melting point of ice is ______ degree Celsius.

Correct Answer: 0

Question 28The melting point of wax is ______ degree Celsius.

Correct Answer: 55

Question 29For a pure substance, the melting point and the ______ point are the same.

Correct Answer: freezing

Question 30During the melting process, the temperature of the substance remains ______.

Correct Answer: constant

Question 31The heat absorbed during a change of state without a rise in temperature is called ______ heat.

Correct Answer: latent

Question 32Latent heat is utilized to increase the ______ energy of the molecules.

Correct Answer: potential

Question 33Water ______ on freezing, unlike wax which contracts.

Correct Answer: expands

Question 34The melting point of ice ______ with an increase in pressure.

Correct Answer: decreases

Question 35The melting point of wax ______ with an increase in pressure.

Correct Answer: increases

Question 36Adding salt to ice lowers its melting point; this mixture is called a ______ mixture.

Correct Answer: freezing

Question 37Change of liquid into gas at a fixed temperature is called ______ or vaporization.

Correct Answer: boiling

Question 38The fixed temperature at which a liquid changes into a vapour is called the ______ point.

Correct Answer: boiling

Question 39The boiling point of water is ______ degree Celsius.

Correct Answer: 100

Question 40Change of vapour into liquid on cooling is called ______.

Correct Answer: condensation

Question 41For a substance, the boiling point and the ______ point are the same.

Correct Answer: condensation

Question 42The boiling point of a liquid ______ with an increase in pressure.

Correct Answer: increases

Question 43Food cooks faster in a pressure cooker because the boiling point of water is ______.

Correct Answer: increased

Question 44It is difficult to cook vegetables on mountains because the boiling point of water ______ due to low pressure.

Correct Answer: decreases

Question 45Adding impurities to a liquid ______ its boiling point.

Correct Answer: increases

Question 46The change of liquid into vapour at all temperatures from the surface is called ______.

Correct Answer: evaporation

Question 47Evaporation is a ______ process, whereas boiling is a rapid process.

Correct Answer: slow

Question 48Evaporation takes place only at the ______ of the liquid.

Correct Answer: surface

Question 49Evaporation causes ______ in the surroundings.

Correct Answer: cooling

Question 50The rate of evaporation increases if the ______ of the liquid is higher.

Correct Answer: temperature
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Short Answer Questions - Practice concise answers to these questions. Click "Show Answer" to reveal the response.
Question 1

What is defined as anything that occupies space and has mass?

Answer:
Matter
Question 2

What did Maharishi Kanada call the tiny particles of matter?

Answer:
Anu
Question 3

What are the tiny particles that make up matter called today?

Answer:
Molecules
Question 4

What is a molecule composed of one atom called?

Answer:
Monoatomic
Question 5

What is the approximate size of a molecule?

Answer:
10^-10 metre
Question 6

What is the space between molecules called?

Answer:
Inter-molecular space
Question 7

What is the force of attraction between molecules called?

Answer:
Inter-molecular force
Question 8

What is the force of attraction between molecules of the same substance?

Answer:
Cohesion
Question 9

What is the force of attraction between molecules of different substances?

Answer:
Adhesion
Question 10

What is the zig-zag motion of suspended particles called?

Answer:
Brownian motion
Question 11

In which state of matter are inter-molecular forces strongest?

Answer:
Solid
Question 12

In which state of matter are inter-molecular spaces largest?

Answer:
Gas
Question 13

Which state of matter has a definite shape and volume?

Answer:
Solid
Question 14

Which state of matter has a definite volume but no definite shape?

Answer:
Liquid
Question 15

Which state of matter has neither definite shape nor volume?

Answer:
Gas
Question 16

What is the process of a solid changing into a liquid?

Answer:
Melting
Question 17

What is the constant temperature at which a solid melts called?

Answer:
Melting point
Question 18

What is the process of a liquid changing into a solid?

Answer:
Freezing
Question 19

What is the melting point of ice?

Answer:
0°C
Question 20

What is the melting point of wax?

Answer:
55°C
Question 21

Does temperature change during the melting process?

Answer:
No
Question 22

What is the heat absorbed during change of state called?

Answer:
Latent heat
Question 23

What is the process of a liquid changing into a gas at a fixed temperature?

Answer:
Boiling
Question 24

What is the boiling point of water?

Answer:
100°C
Question 25

What is the process of a gas changing into a liquid?

Answer:
Condensation
Question 26

What is the process of a solid changing directly into gas?

Answer:
Sublimation
Question 27

What is the process of a gas changing directly into solid?

Answer:
Deposition
Question 28

Name a substance that undergoes sublimation.

Answer:
Camphor
Question 29

What is solid carbon dioxide commonly called?

Answer:
Dry ice
Question 30

Does water expand or contract on freezing?

Answer:
Expand
Question 31

Does wax expand or contract on freezing?

Answer:
Contract
Question 32

What happens to the melting point of ice if pressure increases?

Answer:
Decreases
Question 33

What happens to the boiling point of water if pressure increases?

Answer:
Increases
Question 34

What is a mixture of ice and salt called?

Answer:
Freezing mixture
Question 35

Does adding impurities increase or decrease the boiling point?

Answer:
Increase
Question 36

What is the change of liquid to gas at all temperatures called?

Answer:
Evaporation
Question 37

Where does evaporation take place in a liquid?

Answer:
Surface
Question 38

Does evaporation cause heating or cooling?

Answer:
Cooling
Question 39

How does higher temperature affect evaporation rate?

Answer:
Increases
Question 40

How does higher humidity affect evaporation rate?

Answer:
Decreases
Question 41

What is the boiling point of alcohol?

Answer:
78.3°C
Question 42

What is the boiling point of ether?

Answer:
35°C
Question 43

What is the melting point of copper?

Answer:
1085°C
Question 44

What is the latent heat of fusion of ice?

Answer:
336 x 10^3 J/kg
Question 45

What is the latent heat of vaporization of water?

Answer:
2260 x 10^3 J/kg
Question 46

What is the unit of specific latent heat?

Answer:
Joule per kilogram
Question 47

Which state of matter is highly compressible?

Answer:
Gas
Question 48

Which state of matter is rigid?

Answer:
Solid
Question 49

What kind of motion do molecules in a solid have?

Answer:
Vibrational
Question 50

What instrument is used to observe Brownian motion?

Answer:
Microscope
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Long Answer Questions - Practice detailed answers to these comprehensive questions. Click "Show Answer" to reveal the response.
Question 1

Define matter and explain its composition according to modern scientific theory.

Answer:
Matter is defined as anything that occupies space, has mass, and can be perceived by our senses. Examples include air, water, iron, and milk. According to modern scientific theory, matter is composed of tiny particles called molecules. A molecule is the smallest unit of matter that can exist independently and retains all the physical and chemical properties of that substance. These molecules can be made of atoms of the same kind (as in elements like oxygen) or different kinds (as in compounds like water).
Question 2

Describe an experiment to demonstrate that matter is composed of tiny particles and that there are spaces between them.

Answer:
To demonstrate this, take a 100 mL beaker and fill it half with water. Mark the initial water level on the outside of the beaker. Add some sugar to the water and stir it well with a glass rod until the sugar dissolves completely. Observe the water level again. You will notice that the water level remains the same as the initial mark. This observation leads to two conclusions: first, matter (sugar and water) is made of tiny particles; second, there are empty spaces between the particles of water, known as inter-molecular spaces, which the sugar particles occupy upon dissolving, preventing any rise in volume.
Question 3

List and explain the four main characteristics of the molecules of matter.

Answer:
1. They are very small in size: Molecules are approximately 10^-10 meters in size and cannot be seen even with a microscope. 2. They have spaces between them: There are gaps between molecules called inter-molecular spaces, which vary across states (least in solids, maximum in gases). 3. They are in constant motion: Molecules possess kinetic energy and are always moving (vibrating in solids, moving freely in liquids and gases). 4. They attract each other: Molecules exert an inter-molecular force of attraction on one another, which can be cohesive (between same substances) or adhesive (between different substances).
Question 4

Explain the concept of inter-molecular forces, distinguishing between the force of cohesion and the force of adhesion.

Answer:
Inter-molecular force is the force of attraction existing between the molecules of matter. This force holds the substance together. It is very strong in solids, weaker in liquids, and negligible in gases. The force of attraction between molecules of the same substance is called the force of cohesion (e.g., attraction between water molecules). The force of attraction between molecules of two different substances is called the force of adhesion (e.g., water molecules sticking to a glass surface).
Question 5

Describe an experiment using Potassium Permanganate to show that molecules are very small in size.

Answer:
Dissolve a crystal of potassium permanganate in 100 mL of water. The water will turn a deep pink color. Take 10 mL of this solution and mix it with 90 mL of fresh water. The new solution will still be pink, though lighter. Repeat this dilution process several times. You will observe that the water remains pink even after high dilution. This demonstrates that a single crystal of potassium permanganate must be made of millions of tiny particles capable of spreading out and coloring a large volume of water, proving that particles of matter are extremely small.
Question 6

What is Brownian motion? Describe an experiment to demonstrate it.

Answer:
Brownian motion is the random, zig-zag motion of particles suspended in a fluid (liquid or gas) resulting from their collision with the fast-moving atoms or molecules in the gas or liquid. To demonstrate this, take a beaker with water and sprinkle some lycopodium powder on the surface. Illuminate the beaker with a lamp and observe the surface through a microscope. You will see the fine lycopodium particles moving rapidly in a random, zig-zag path. This happens because the invisible, constantly moving water molecules collide with the lycopodium particles, pushing them in different directions.
Question 7

Differentiate between solids, liquids, and gases based on their volume and shape.

Answer:
Solids have a definite shape and a definite volume because their molecules are fixed in position and held by strong forces. Liquids have a definite volume but no definite shape; they take the shape of the container they are poured into because their molecules can move within the boundary of the liquid. Gases have neither a definite shape nor a definite volume; they fill the entire space available to them because their molecules are free to move in all directions.
Question 8

Explain the molecular model of solids.

Answer:
In the molecular model of solids: 1. Molecules are very closely packed, meaning inter-molecular spaces are very small. 2. The molecules are arranged in a fixed, rigid pattern. 3. The inter-molecular forces of attraction are very strong, holding the molecules firmly in place. 4. The molecules do not move from their positions but only vibrate to and fro about their mean positions. This rigid arrangement gives solids their definite shape and volume.
Question 9

Explain the molecular model of liquids.

Answer:
In the molecular model of liquids: 1. The molecules are less closely packed than in solids, meaning inter-molecular spaces are larger. 2. The molecules are not arranged in a rigid pattern. 3. The inter-molecular forces are weaker than in solids, allowing molecules to slide over one another. 4. Molecules are free to move within the boundary of the liquid but cannot easily escape it. This freedom allows liquids to flow and take the shape of their container while maintaining a fixed volume.
Question 10

Explain the molecular model of gases.

Answer:
In the molecular model of gases: 1. The molecules are very far apart, meaning inter-molecular spaces are very large compared to solids and liquids. 2. The inter-molecular forces of attraction are negligible (extremely weak). 3. The molecules move freely and randomly in all directions at high speeds. 4. Because there are almost no forces holding them back, gas molecules fill the entire available space, resulting in no fixed shape or volume.
Question 11

Compare solids, liquids, and gases in terms of compressibility and fluidity.

Answer:
Solids are practically incompressible because their molecules are closely packed with little space to move closer, and they cannot flow (they are rigid). Liquids are slightly compressible and can flow from a higher level to a lower level because their molecules can slide over one another. Gases are highly compressible because of the large inter-molecular spaces between particles, and they can flow freely in all directions.
Question 12

Define 'Change of State' and explain the terms Melting and Freezing.

Answer:
Change of state is the process by which a substance changes from one physical state to another (e.g., solid to liquid) at a constant temperature by absorbing or rejecting heat. Melting (or fusion) is the change from a solid state to a liquid state on heating at a fixed temperature called the melting point. Freezing is the reverse process, where a liquid changes into a solid state on cooling at a fixed temperature called the freezing point.
Question 13

Explain why the temperature of a substance remains constant during the process of melting.

Answer:
During melting, heat energy is supplied to the substance, but the temperature does not rise. This is because the heat energy absorbed is used to overcome the strong inter-molecular forces of attraction holding the solid particles together. The energy increases the potential energy of the molecules (increasing their separation) rather than their kinetic energy (which would raise the temperature). This heat is called latent heat.
Question 14

Describe an experiment to determine the melting point of wax.

Answer:
Put some wax in a test tube and clamp it in a vertical stand. Place the test tube in a beaker of water set on a tripod stand with a burner. Insert a thermometer into the wax. Heat the water and record the temperature of the wax every minute. You will observe the temperature rise until it reaches 55 degrees Celsius. At this point, the wax starts melting, and the temperature remains stationary at 55 degrees Celsius until all the wax has melted. This constant temperature is the melting point of wax.
Question 15

What is vaporization? Differentiate between the two types of vaporization.

Answer:
Vaporization is the change from a liquid state to a gaseous state by the absorption of heat. The two types are Boiling and Evaporation. Boiling occurs at a fixed temperature (boiling point), takes place throughout the entire mass of the liquid, and is a rapid process. Evaporation occurs at all temperatures, takes place only at the surface of the liquid, and is a slow, gradual process.
Question 16

Define Boiling Point and describe an experiment to demonstrate the boiling point of water.

Answer:
The boiling point is the constant temperature at which a liquid changes into a vapor without any further increase in temperature. To demonstrate this for water, take water in a beaker and heat it while measuring the temperature with a thermometer. The temperature will rise until it reaches 100 degrees Celsius. At this stage, the water boils vigorously, producing bubbles of steam. Even though heat is still being supplied, the temperature will remain constant at 100 degrees Celsius until all the water has vaporized.
Question 17

Explain the molecular mechanism of evaporation.

Answer:
In a liquid, molecules are in constant motion and collide with each other. During these collisions, some molecules near the surface acquire higher kinetic energy than average, sufficient to overcome the attractive forces of other molecules. These high-energy molecules escape from the liquid surface into the atmosphere. This escape of molecules from the surface constitutes evaporation.
Question 18

List five factors that affect the rate of evaporation of a liquid and explain how each affects it.

Answer:
1. Temperature of liquid: Higher temperature increases the kinetic energy of molecules, increasing the rate of evaporation. 2. Area of exposed surface: A larger surface area allows more molecules to escape simultaneously, increasing the rate. 3. Nature of liquid: Volatile liquids (like alcohol) with weaker intermolecular forces evaporate faster than water. 4. Flow of air (wind): Moving air carries away vapor molecules from the surface, preventing saturation and speeding up evaporation. 5. Humidity: High humidity means the air is already saturated with moisture, which decreases the rate of evaporation.
Question 19

Why does evaporation produce cooling? Explain with an example.

Answer:
Evaporation produces cooling because the molecules that escape the liquid surface are those with the highest kinetic energy. To escape, they absorb heat energy (latent heat) from the remaining liquid or the surroundings. This loss of heat energy lowers the temperature of the liquid and its surroundings. For example, if you pour a drop of spirit on your hand, it evaporates rapidly by taking heat from your skin, leaving your hand feeling cool.
Question 20

Why do doctors advise putting strips of wet cloth on the forehead of a patient with high fever?

Answer:
Doctors advise this because the water in the wet cloth evaporates. The process of evaporation requires heat, which is absorbed from the patient's forehead (body). As the water evaporates, it draws out the body heat, thereby lowering the temperature of the patient's body and providing relief from the fever.
Question 21

Why is water kept in earthen pots (surahi) in summer to cool it?

Answer:
Earthen pots have many tiny pores in their walls. Water seeps out through these pores to the outer surface of the pot. This water evaporates by absorbing the necessary heat from the water remaining inside the pot and the pot itself. This continuous loss of heat due to evaporation causes the temperature of the water inside the pot to decrease, keeping it cool.
Question 22

What is sublimation? Give three examples of substances that sublime.

Answer:
Sublimation is the process by which a solid changes directly into its gaseous (vapor) state on heating, without passing through the liquid state. Conversely, the vapor changes directly back to solid on cooling. Examples of substances that sublime include camphor, ammonium chloride, iodine, naphthalene, and solid carbon dioxide (dry ice).
Question 23

Describe an experiment to demonstrate the sublimation of ammonium chloride.

Answer:
Place some powdered ammonium chloride in a china dish. Cover the dish with an inverted funnel and plug the stem of the funnel with cotton to prevent vapors from escaping. Heat the china dish using a burner. You will observe white fumes rising inside the funnel. These are vapors of ammonium chloride. As these vapors rise and touch the cooler upper walls of the funnel, they cool down and deposit as solid ammonium chloride. This demonstrates the direct change from solid to gas and back to solid.
Question 24

Differentiate between Evaporation and Boiling based on temperature, speed, and location.

Answer:
1. Temperature: Evaporation takes place at all temperatures, whereas boiling takes place only at a specific, constant temperature (boiling point). 2. Speed: Evaporation is a slow and gradual process, whereas boiling is a rapid and violent process. 3. Location: Evaporation is a surface phenomenon occurring only at the liquid's surface, whereas boiling is a bulk phenomenon occurring throughout the entire mass of the liquid.
Question 25

Explain why steam causes more severe burns than boiling water at the same temperature.

Answer:
Steam at 100 degrees Celsius contains significantly more heat energy than boiling water at 100 degrees Celsius. This extra energy is the 'latent heat of vaporization' that was absorbed to convert the water into steam. When steam comes into contact with skin, it condenses back to water and releases this large amount of latent heat (2260 Joules per gram) in addition to the heat of the hot water, causing much more severe burns.
Question 26

What is Latent Heat? Why is it called 'hidden' heat?

Answer:
Latent heat is the amount of heat energy absorbed or released by a substance during a change of state (e.g., solid to liquid, liquid to gas) without any change in its temperature. It is called 'latent' (meaning hidden) because this heat does not manifest as a rise in temperature on a thermometer; instead, it is 'hidden' in the substance as increased potential energy of the molecules.
Question 27

Explain the effect of pressure and impurities on the boiling point of a liquid.

Answer:
1. Effect of Pressure: The boiling point of a liquid increases with an increase in pressure. For example, in a pressure cooker, water boils at a temperature higher than 100 degrees Celsius because of the increased pressure. 2. Effect of Impurities: Adding impurities to a liquid generally increases its boiling point. For example, adding salt to water raises its boiling point above 100 degrees Celsius.
Question 28

Explain the effect of pressure and impurities on the melting point of a solid.

Answer:
1. Effect of Pressure: For substances that expand on freezing (like water), the melting point decreases with increased pressure. For substances that contract on freezing (like wax), the melting point increases with increased pressure. 2. Effect of Impurities: Adding impurities to a solid decreases its melting point. For example, adding salt to ice lowers its melting point significantly below 0 degrees Celsius.
Question 29

What is a freezing mixture? Give an example and its use.

Answer:
A freezing mixture is a mixture of substances (usually ice and a salt) that produces a temperature significantly lower than the freezing point of the pure solvent. A common example is a mixture of ice and common salt. When salt is added to ice, the melting point of ice is lowered, and the mixture can reach temperatures as low as -21 degrees Celsius. This is used in making ice creams (kulfi) to freeze the mixture quickly.
Question 30

Why do wet clothes dry faster on a windy day?

Answer:
On a windy day, the moving air (wind) sweeps away the water vapor molecules that have just evaporated from the surface of the clothes. This prevents the air near the clothes from becoming saturated with humidity. By constantly replacing humid air with drier air, the rate of evaporation is maintained at a high level, causing the clothes to dry faster.
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Quick Review Flashcards - Click to flip and test your knowledge!
Question
According to the kinetic theory of matter, what are all substances made of?
Answer
All substances are made of tiny particles (molecules) that are always in a state of motion.
Question
In which state of matter do particles have the least energy and move slow or not at all?
Answer
Solid.
Question
In which state of matter do particles have much more energy and move freely at high speeds?
Answer
Gas.
Question
What is the effect of heating an object on the movement or energy of its particles?
Answer
Heating increases the movement or energy of the particles.
Question
What is the effect of cooling an object on the movement or energy of its particles?
Answer
Cooling decreases the energy of the particles.
Question
What is the scientific definition of matter?
Answer
Matter is something which occupies space, has mass and can be perceived by our senses.
Question
What did the ancient Indian philosopher Maharishi Kanada consider matter to be made of?
Answer
He considered matter to be made up of tiny particles which he called 'anu'.
Question
Modern science has established that matter is composed of tiny particles called _____.
Answer
molecules
Question
What is a molecule?
Answer
A molecule is the smallest particle of a substance that can exist freely in nature and has all the properties of that substance.
Question
A molecule composed of only one atom, such as helium or neon, is called a _____ molecule.
Answer
monoatomic
Question
A molecule composed of two atoms, such as hydrogen or oxygen, is called a _____ molecule.
Answer
diatomic
Question
A molecule composed of more than two atoms, such as water or ammonia, is called a _____ molecule.
Answer
polyatomic
Question
What is the approximate size of a single molecule?
Answer
A molecule is of the order of $10^{-10}$ metres in size.
Question
The spacing between the molecules of matter is called _____ space.
Answer
inter-molecular
Question
In which state of matter is the inter-molecular space the least?
Answer
Solids.
Question
In which state of matter is the inter-molecular space the most?
Answer
Gases.
Question
What characteristic of molecules explains why the water level doesn't change when sugar dissolves in it?
Answer
The sugar particles occupy the inter-molecular spaces between the water particles.
Question
The energy possessed by molecules due to their constant state of motion is called _____ energy.
Answer
kinetic
Question
How do molecules move in a solid?
Answer
They vibrate about their mean positions but do not leave their positions.
Question
How do molecules move in a liquid?
Answer
They are free to move well within the boundary of the liquid.
Question
How do molecules move in a gas?
Answer
They can move in a random manner everywhere in the space available to them.
Question
The force of attraction that molecules of matter exert on each other is called _____ force.
Answer
inter-molecular
Question
The inter-molecular force of attraction is effective only up to a separation of about _____ metres.
Answer
$10^{-9}$
Question
Term: Force of Cohesion
Answer
The inter-molecular force of attraction between the molecules of the same substance.
Question
Term: Force of Adhesion
Answer
The force of attraction between the molecules of two different substances.
Question
Why is it difficult to break a piece of coal into small particles?
Answer
The particles of coal are bound by the strong forces of attraction amongst themselves (cohesion).
Question
What are the three physical states of matter?
Answer
Solid, liquid, and gas.
Question
Which state of matter has a definite size (volume) and a definite shape?
Answer
Solid.
Question
Which state of matter has a definite volume but no definite shape?
Answer
Liquid.
Question
Which state of matter has neither a definite volume nor a definite shape?
Answer
Gas.
Question
In solids, the inter-molecular force is very _____, and kinetic energy is very _____.
Answer
strong, small
Question
In liquids, the inter-molecular force is not much _____, and kinetic energy is sufficient for molecules to move.
Answer
strong
Question
In gases, the inter-molecular force is _____ and kinetic energy is very _____.
Answer
negligible, high
Question
Why do solids have a definite shape?
Answer
Their molecules are in fixed positions due to strong inter-molecular forces and do not leave their positions.
Question
Why can liquids flow?
Answer
The liquid molecules can slide over one another due to weaker inter-molecular forces compared to solids.
Question
Why do gases fill the entire container they are in?
Answer
Gas molecules are quite free to move anywhere because of their very weak inter-molecular forces.
Question
Which state of matter is characterized by molecules that can only vibrate to and fro about their mean positions?
Answer
Solid.
Question
Which state of matter is characterized by loosely packed molecules whose positions are not fixed?
Answer
Liquid.
Question
Which state of matter is characterized by molecules that are wide apart and have positions that are not fixed?
Answer
Gas.
Question
Term: Change of State
Answer
The process of change from one state to another either by absorption or rejection of heat at a constant temperature.
Question
What is the process of a solid changing into a liquid upon heating at a fixed temperature called?
Answer
Melting or fusion.
Question
What is the process of a liquid changing into a solid upon cooling at a fixed temperature called?
Answer
Freezing.
Question
What is the process of a liquid changing into a gas (or vapour) upon heating at a fixed temperature called?
Answer
Boiling or vaporization.
Question
What is the process of a gas (or vapour) changing into a liquid upon cooling at a fixed temperature called?
Answer
Condensation.
Question
Term: Sublimation
Answer
The process by which a solid on heating directly changes into its vapour or gaseous state without changing into liquid.
Question
Term: Deposition
Answer
The process where a gas on being cooled directly changes into a solid.
Question
The heat absorbed or rejected during a change of state, which does not cause a change in temperature, is called _____ heat.
Answer
latent
Question
Term: Melting Point
Answer
The fixed temperature at which a solid changes into liquid without further increase in temperature.
Question
What is the melting point of ice?
Answer
$0^{\circ}$C.
Question
Term: Freezing Point
Answer
The fixed temperature at which a liquid changes into a solid state by rejecting heat.
Question
For a pure substance, how does the melting point compare to the freezing point?
Answer
The melting point and freezing point are the same.
Question
What happens to the kinetic energy of molecules when a solid is heated up to its melting point?
Answer
The kinetic energy increases, causing the molecules to vibrate more violently.
Question
During melting, the absorbed heat energy is used to do work against the forces of attraction, increasing the _____ of the molecules.
Answer
potential energy
Question
Term: Boiling Point
Answer
The fixed temperature at which a liquid changes into vapour without further increase in temperature.
Question
What is the boiling point of pure water at standard pressure?
Answer
$100^{\circ}$C.
Question
Term: Condensation Point
Answer
The temperature at which a vapour changes into liquid without any further decrease in temperature.
Question
How does increasing the pressure on a liquid affect its boiling point?
Answer
The boiling point of a liquid increases with an increase of pressure on it.
Question
Why does it take longer to cook vegetables at high altitudes?
Answer
At high altitudes, the atmospheric pressure is low, so water boils at a temperature lower than $100^{\circ}$C.
Question
Term: Evaporation
Answer
A process by which a liquid changes into vapour at all temperatures from the surface of the liquid.
Question
How does evaporation differ from boiling in terms of temperature?
Answer
Evaporation takes place at all temperatures, while boiling takes place only at a fixed temperature (the boiling point).