Case study ( 4 Marks )

Question 14 Marks

You must have observed that the rate of evaporation increases with–

an increase of surface area:
We know that evaporation is a surface phenomenon. If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out.
an increase of temperature:

With the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state.
In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings makes the surroundings cold. What happens when you pour some acetone (nail polish remover)$ on your palm? The particles gain energy from your palm or surroundings and evaporate causing the palm to feel cool. After a hot sunny day, people sprinkle water on the roof or open ground because the large latent heat of vaporization of water helps to cool the hot surface.
$i.)$ Evaporation is surface phenomenon. True or false
$a.)$ True
$b.)$ False
$c.)$ None of these
$ii.)$ As temperature increases the rate of evaporation is
$a.)$ increases
$b.)$ decreases
$c.)$ remains constant
$d.)$ None of these
$iii.)$ The rate of evaporation increases with
$a.)$ Increase in wind speed
$b.)$ Decrease in wind speed
$c.)$ Does not have any effect from wind speed
$d.)$ None of these
$iv.)$ What happens when you pour some acetone (nail polish remover) on your palm?
$v.)$ We are able to sip hot tea from saucer than from cup. Why?

Answer

$i.) $aii.) a
$iii.)$ a
$iv.)$ The particles gain energy from your palm or surroundings and evaporate causing the palm to feel cool.
$v.)$ We are able to sip hot tea from saucer than from cup. This is because saucer has large surface area, due to large surface area as compare to cut area tea evaporates at faster rate

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Question 24 Marks

Do we always need to heat or change pressure for changing the state of matter? Can you quote some examples from everyday life where change of state from liquid to vapour takes place without the liquid reaching the boiling point? In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour. This phenomenon of change of a liquid into vapors at any temperature below its boiling point is called evaporation.
$i.)$ Evaporation of liquid takes place at
$a.)$ Boiling point
$b.)$ Above boiling point
$c.)$ Below boiling point
$d.)$ None of these
$ii.)$ Evaporation takes place at surface of liquid because
$a.)$ They are heavy as compare to other particles
$b.)$ They have sufficient kinetic energy to break the force
$c.)$ They are light weight as compare to other particles
$d.)$ None of these
$iii.)$ During evaporation particles of liquid change into vapour
$a.)$ From the surface
$b.)$ From the bottom
$c.)$ From all over the liquid
$d.)$ None of these
$iv.)$ Define evaporation.
$v.)$ Explain process of evaporation

Answer

$i.)$ cii.) b
$iii.)$ a
$iv.)$ The phenomenon of change of a liquid into vapors at any temperature below its boiling point is called evaporation.
$v.)$ In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour. This phenomenon of change of a liquid into vapors at any temperature below its boiling point is called evaporation.

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Question 34 Marks

What happens inside the matter during change of state? On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, theParticles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid. The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
The temperature of the system does not change after the melting point is reached, till all the ice melts. This happens even though we continue to heat the beaker, that is, we continue to supply heat. This heat gets used up in changing the state by overcoming the forces of attraction between the particles. The amount of heat energy that is required to change $1 \ kg$ of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion. So, particles in water at $0^0 C (273 K)$$ have more energy as compared to particles in ice at the same temperature.
The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point. Boiling is a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to change into the vapour state. A change of state directly from solid to gas without changing into liquid state is called sublimation and the direct change of gas to solid without changing into liquid is called deposition.
$i.)$ A change of state directly from solid to gas without changing into liquid state is called
$a.)$ Sublimation
$b.)$ Deposition
$c.)$ Boiling point
$d.)$ None of these
$ii.)$ The direct change of gas to solid without changing into liquid is called
$a.)$ Sublimation
$b.)$ Deposition
$c.)$ Boiling point
$d.)$ None of these
$iii.)$ The energy supplied by heat to solid is used to overcome the forces of attraction between the particles. True or false
$a.)$ True
$b.)$ False
$c.)$ None of these
$iv.)$ Define melting point and boiling point
$v.)$ Define latent heat of fusion

Answer

$i.)$ aii.) b
$iii.)$ a
$iv.)$ The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.
$v.)$ The amount of heat energy that is required to change $1 \ kg$ of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion.

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Question 44 Marks

There are three states of matter – solid, liquid and gas.
Solids have a definite shape, distinct boundaries and fixed volumes, that is, have negligible compressibility. Solids have a tendency to maintain their shape when subjected to outside force. Solids may break under force but it is difficult to change their shape, so they are rigid.
Liquids have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept. Liquids flow and change shape, so they are not rigid but can be called fluid.
Gas as has indefinite shape, no fixed volume. Gas gets the shape and volume of container.
Gas has very low density hence are light. Gas can flow easily and hence are called fluid.
$i.)$ Which of the following state of matter takes shape of container in which it is filled?
$a.)$ Solid
$b.)$ Liquid
$c.)$ Gas
$d.)$ Both $b$ and $c$
$ii.)$ Distance between particles of matter least in
$a.)$ Solid
$b.)$ Liquid
$c.)$ Gas
$d.)$ None of these
$iii.)$ Compressibility is least in case of
$a.)$ Solid
$b.)$ Liquid
$c.)$ Gas
$d.)$ None of these
$iv.)$ Give properties of solids.
$v.)$ Give properties of Gases.

Answer

$i.)$ dii.) a
$iii.)$ a
$iv.)$ properties of solid are given below

Solid has fixed volume.
Solid has fixed shape.
Solid has high density.
Solids are heavy.
Solid does not flow.

$v.)$ Properties of gases are

Gas has indefinite shape
Gas has no fixed volume.
Gas gets the shape and volume of container.
Gas fills the container completely.
Gas has very low density.
Because of low density gas are light.
Gas can flow easily and hence are called fluid.

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Question 54 Marks

A matter is anything that has mass and occupies space. Pen, paper, clips, sand, air, ice, etc. are different forms of matter. Every matter is made up of small particles. These particles are so tiny that they can’t be seen with naked eyes. Let’s see about the different characteristics of particles of matter.

All matter is made up of very small particles.
.Particles of matter has spaces between them.
Particles of matter are continuously moving.
Particles of matter attract each other.

Answer the following questions by referring above paragraph.
$i.)$ Which of following is not matter?
$a.)$ Pen
$b.)$ air
$c.)$ smell of perfume
$d.)$ None of these
$ii.)$ Thoughts coming in our mind are example of matter. True or false
$a.)$ True
$b.)$ False
$c.)$ None of these
$iii.)$ Which of the following is true about particles of matter?
$a.)$ Particles of matter has spaces between them
$b.)$ Particles of matter are continuously moving
$c.)$ Particles of matter attract each other
$d.)$ All of these
$iv.)$ Give 5 examples of matter in our surroundings
$v.)$ Enlist all properties of particles of matter

Answer

$i.)$ cii.) b
$iii.)$ d
$iv.)$ pen, pencil, notebook, ice and water
$v.)$ Different characteristics of particles of matter are

All matter is made up of very small particles.
.Particles of matter has spaces between them.
Particles of matter are continuously moving.
Particles of matter attract each other

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Science Case study ( 4 Marks )

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