STD: IX
Matter in Our Surroundings
I . Answer the following:
1. What produces more severe burns, boiling water or steam?
ans. The particles in steam at 373 0K have more energy than water at the same temperature. This is
because the particles in steam have absorbed extra energy in the form of latent heat of vaporization. So,
when steam comes in contact with the skin, it releases more heat than the boiling water would do at the
same temperature. As a result steam at 373 0 K causes more severe burns than boiling water at the same
temperature.
2. Why are we able to sip hot tea milk faster from a saucer rather than a cup?
ans. We are able to sip hot tea faster from a saucer rather than a cup because a saucer has a greater surface are.
As a result the rate of evaporation increases and cools the tea.
3. When some salt is dissolved in water the volume of water does not increase. Why?
ans. When some salt is dissolved in water the volume of water does not increase because the salt particles
occupy the spaces between the particles of water.
4. What is sublimation?
ans. Sublimation is the change of state directly from a solid to a gas without passing through the liquid
state.
5. How does the water kept in an earthen pot(matka) become cool during summer?
ans. An earthen pot has a large number of extremely small pores. Water seeps out through them and evaporates
from the surface of the pot, thereby cooling the whole system. The latent heat required for evaporation is taken
from the water in the pot. As a result water becomes cool.
6. What is evaporation?
ans. Evaporation is the phenomenon of the change of liquid into vapour at any temperature below the
boiling point of the liquid.
7. A diver is able to cut through water in a swimming pool. Which property of matter does this
observation show?
ans. This shows that liquids are compressible. The intermolecular space between the particles of liquids is
greater as compared to the solids. Hence when the diver dives into water the particles of water get compressed.
II. Give Reasons:
1. Naphthalene balls disappear with time without leaving any solid.
ans. Naphthalene balls disappear with time without leaving any solid because they undergo sublimation
i.e. they directly change into vapour without passing through the liquid state.
2. Clothes dry faster in the sun than in the shade.
ans. Evaporation takes place faster when the temperature in increased. The temperature is higher in the
sun than in the shade. Therefore, clothes dry faster in the sun than in the shade.
3. A wet strip of cloth is placed on the forehead of person having high fever.
ans. Evaporation produces cooling. The water in the wet strip of cloth placed on the forehead evaporates.
The heat needed for evaporation is absorbed from the body, as a result the temperature of the person
having high fever comes down.
4. A gas completely fills the vessel in which it is kept.
ans. A gas completely fills the vessel in which it is kept due to the large intermolecular space between the
gaseous particles and high kinetic energy of the particles. Moreover the gas is fluid.
5. It is advisable to wear cotton clothes in summer.
ans. Cotton is good absorber of water and therefore readily absorbs the sweat. When the sweat
evaporates, it absorbs the heat from the body and cools it.
6. A solid melts when heated.
ans. When a solid is heated, the kinetic energy of the particles increases, as a result they vibrate with
greater speed. When the kinetic energy of the particles overcomes the forces of attraction between the
particles, they leave their fixed positions and begin to move freely i.e. the solid melts.
7. When a solid begins to melt, its temperature does not rise though the heating is continued.
ans. When a solid begins to melt, its temperature does not rise though the heating is continued because
the heat which is supplied is used up for changing the state of the solid by overcoming the forces of
attraction between the particles.
8. Our palm feel cold when we put some acetone or petrol or perfume on it?
ans. When we put acetone on our palm the particles gain energy from the palm or surroundings and leave the
surface of the palm giving a cool feeling.
Karuna Saraswat Sharma
09527915212
STD: IX
Matter in Our Surroundings
9. Water at room temperature is a liquid.
ans. Water at room temperature is a liquid because it does not have a fixed shape. It takes the shape of the
container in which it is poured. Secondly it can flow easily, hence it is not rigid but a fluid.
10. An iron almirah is a solid at room temperature.
ans. An iron almirah is a solid because it has a definite shape and a fixed volume. It does not flow, hence it
is rigid.
11. Diffusion is faster if the temperature is increased.
ans. When the temperature is increased the kinetic energy of the particles increases, they move faster and
therefore the diffusion is also faster.
12. Clothes dry faster in winter than in the rainy season, though the temperature is almost the same.
ans. The rate of evaporation takes place faster when the humidity decreases. In winter the humidity is less
than that in the rainy season. Therefore, in winter the clothes dry faster than in the rainy season, though
the temperature is almost the same.
13. We can easily move our hand in air but to do the same through a solid block of wood we need a
karate expert.
ans. The particles of air have weak intermolecular force of attraction. They also have a large intermolecular
space between them. As a result we can easily move our hand in air. In case of a solid block of wood or brick
the particles are closely packed having a strong intermolecular force of attraction and very little intermolecular
space. Hence, it is difficult to move our hand through it.
14. Though a sponge is a solid, it can be compressed.
ans. A sponge has minute holes in which the air is trapped. When it is pressed, the air from the holes
escapes and therefore it can be compressed.
15. The rate of diffusion in liquids is higher than that in solids.
ans. The rate of diffusion in liquids is higher than that in solids because the particles of a liquid can move
freely and the space between the particles of a liquid is more than that in solids.
16. Droplets of water are formed on the outer surface of a glass containing ice-cold water.
ans. When the water vapour present in the air comes in contact with the cold surface of the glass, the
vapour particles lose energy and are converted into the liquid state. Therefore, droplets of water are
formed on the outer surface of a glass containing ice-cold water.
17. Gases are highly compressible.
ans. Gases are highly compressible because the space between the particles of a gas is maximum among
the three states of matter. When pressure is applied the particles come closer to one another.
18. The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food
you haveto go close.
ans. The rate of diffusion is very high in case of gases. The particles of hot sizzling food mixes with the
particles of air and reaches us several meters away. In case of cold food the food particles do not mix with the
particles of air easily. The temperature increases the rate of diffusion. Hence we have to go close to it ito get
the smell.
19. Burns caused by steam are more severe than those caused by boiling water.
ans. In comparison to boiling water, steam has absorbed extra heat energy in the form of latent heat of
vaporization. Therefore burns caused by steam are more severe than those caused by boiling water.
20. Solid carbon dioxide is called dry ice.
ans. Solid carbon dioxide is directly converted to the gaseous state without passing through the liquid
state under 1 atmospheric pressure. Therefore solid carbon dioxide is called dry ice.
21. A gas exerts pressure on the walls of the container.
ans. The kinetic energy of the particles in the gaseous state is the maximum. Particles move about randomly at
high speed. Due to this random movement the particles hit each other and also the walls of the container. The
pressure exerted by the gas is because of this force exerted by the gas particles per unit area of the container.
22. When wet clothes are to be dried, they are spread out.
ans. The rate of evaporation depends on the area of the exposed surface. When the wet clothes are
spread out, the exposed area increases, the evaporation is faster thereby frying the clothes.
23. The pressure of an enclosed gas increases when it is heated.
ans. When an enclosed gas is heated, the kinetic energy of the particles increases. The particles move
faster and exert greater force on the walls of the container resulting in an increase of pressure.
III. Distinguish between :
Karuna Saraswat Sharma
09527915212
Matter in Our Surroundings
STD: IX
1. Solid state and Liquid state
Solid state
Liquid state
i. Solids have a
i. Liquids do not have a definite shape. They take the shape of the
definite shape.
ii. Solids are rigid.
container in which they are placed.
ii.
Liquids are not rigid. They are fluid.
2. Evaporation and Boiling
Evaporation
i. Evaporation occurs only at the surface of the liquid.
Boiling
i. Boiling is a bulk phenomenon.
ii. Evaporation occurs at any temperature below boiling
point.
ii. A liquid boils only at its boiling point.
Karuna Saraswat Sharma
09527915212