Chapter 1
Matter in our surroundings
Intext questions and answers
Page no 3:
1) Which of the following are matter: chair, air, love, smell, hate, almonds, thoughts, cold drink, the smell of perfume?
Ans: Anything which occupies space has mass and can be felt by any one of five senses is called matter. Therefore chair, air, smell, almonds, cold drinks, and smell of perfume are matter. Smell is matter because it is due to the presence of some volatile substances in the air.
2) Give a reason for the following observations: the smell of hot sizzling food reaches you several metres away but to get the smell from cold food you have to go close.
Ans: The particles of matter possess kinetic energy and thus are constantly moving. At low temperature the kinetic energy is low and hence the particles move slowly. But as the temperature rises, the kinetic energy increases and hence the particles move faster. Now since the particles of hot vapours coming out of hot sizzling food move faster, therefore, they easily reach us even when we are several metres away. On the other hand, the particles of vapours coming out of cold food travel only slowly hence do not reach us. Therefore, to get the smell from cold food we have to go close to the food.
3) A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Ans: The diver is able to cut through water in the swimming pool because matter is made up of particles which have vacant spaces between them. Moreover, the attractive forces between molecules of water are not very strong. The diver can easily cut through the water by applying force to displace water and occupy its place. This observation shows that particles of matter attract each one other.
4) What are the characteristics of the particles of matter?
Ans:
1) Which of the following are matter: chair, air, love, smell, hate, almonds, thoughts, cold drink, the smell of perfume?
Ans: Anything which occupies space has mass and can be felt by any one of five senses is called matter. Therefore chair, air, smell, almonds, cold drinks, and smell of perfume are matter. Smell is matter because it is due to the presence of some volatile substances in the air.
2) Give a reason for the following observations: the smell of hot sizzling food reaches you several metres away but to get the smell from cold food you have to go close.
Ans: The particles of matter possess kinetic energy and thus are constantly moving. At low temperature the kinetic energy is low and hence the particles move slowly. But as the temperature rises, the kinetic energy increases and hence the particles move faster. Now since the particles of hot vapours coming out of hot sizzling food move faster, therefore, they easily reach us even when we are several metres away. On the other hand, the particles of vapours coming out of cold food travel only slowly hence do not reach us. Therefore, to get the smell from cold food we have to go close to the food.
3) A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Ans: The diver is able to cut through water in the swimming pool because matter is made up of particles which have vacant spaces between them. Moreover, the attractive forces between molecules of water are not very strong. The diver can easily cut through the water by applying force to displace water and occupy its place. This observation shows that particles of matter attract each one other.
4) What are the characteristics of the particles of matter?
Ans:
- Particles of matter have space between them
- Particles of matter are continuously moving
- Particles of matter attract each other
Page no 6
1. The mass per unit volume of a substance is called density. (density = mass / volume) arrange the following in order of increasing density
air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Ans: The order of increasing density is :
air < exhaust from chimney < cotton < water < honey < chalk < iron
1. The mass per unit volume of a substance is called density. (density = mass / volume) arrange the following in order of increasing density
air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Ans: The order of increasing density is :
air < exhaust from chimney < cotton < water < honey < chalk < iron
2) Give reason
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in the air but to do the same through a solid block of wood we need a karate expert.
Ans (a): The particles of a gas are constantly moving in all the directions with different speeds; therefore, they do not have a fixed volume and hence completely fill the vessel in which they are kept.
(b) The particles of a gas are constantly moving in all directions with different speeds as a result of this random motion the particles of gas collide with one another and also against the walls of the container. As a result of these collisions, missions the gas exerts some force on the walls of the container. This force per unit area is called pressure of the gas. Thus, gases exert pressure due to the Collisions conditions of the particles of the gas on the walls of the containing vessel.
(c)
(d) We can easily move our hand in the air since the forces of attraction between the particles of gas (that is air) are very weak and hence can be easily were overcome for the movement of the hand. In contrast, the particles of a solid are closely packed and hence the inter particles of forces of attraction are very strong. As a result, they cannot be easily overcome for the movement of the hand. In other words, we need a karate expert with almost incredible power to separate these particles apart.
3) Liquids generally have lower density as compare to solids. But you must have observed that ice floats on water. Find out why?
Ans: Ice has a cage-like structure that is when water freezes to form ice a number of empty spaces are created. As a result, volume increases for the same mass of water. In other words, mass per unit volume and density of ice is lower than that of water and hence ice floats over water.
Page no 9
1) Convert the following temperature to Celsius scale:
(a) 300 K (b) 573K
Ans: (a) 0c=0k-273=300-273=270c
(b) 0c=0k-273=573-273=3000c
2) What is the physical state of water at
(a)250°c (b)1000c
Ans: (a) gaseous state.
(b) Gaseous state.
3) For any substance why does the temperature remained constant during the change of state?
Ans: The temperature remains constant during the change of a state because the heat energy supplied to the substance is used in overcoming the forces of attraction between the particles of that state. As a result, the thermometer does not show any rise in temperature until the entire substance undergoes a change of state.
(a) 300 K (b) 573K
Ans: (a) 0c=0k-273=300-273=270c
(b) 0c=0k-273=573-273=3000c
2) What is the physical state of water at
(a)250°c (b)1000c
Ans: (a) gaseous state.
(b) Gaseous state.
3) For any substance why does the temperature remained constant during the change of state?
Ans: The temperature remains constant during the change of a state because the heat energy supplied to the substance is used in overcoming the forces of attraction between the particles of that state. As a result, the thermometer does not show any rise in temperature until the entire substance undergoes a change of state.
4) Suggest a method to liquify atmospheric gases.
Ans: The atmospheric gases can be liquified by cooling under pressure.
Page no 10
1) Why does a desert cooler cool better on a hot dry day?
Ans: On a hot dry day the humidity (amount of water vapour in the air) is less and therefore, rate of evaporation is more. Since we know that evaporation causes cooling, therefore, as the rate of evaporation is more on a hot dry day, therefore, the desert cooler cool better.
2) How does the water kept in an earthen pot (Matka) becomes cool during summer?
Ans: Earthen port has many small pores present in its walls, from which water oozes out slowly. As water comes out on the outer surface of Matka it evaporates. Since evaporation causes cooling, therefore, water kept in earthen pot become cold.
3) Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Ans: As we put any of these on our palm, the particles of the substances absorb energy from the palm and evaporates. Therefore, it causes cooling and we feel the sensation of cooling. Acetone, petrol or perfume or low boiling liquids.
4) Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Ans: The surface area of hot tea or milk in a saucer is more than a cup. Because of the larger surface area, cooling will be more rapid in a saucer than a cup. Hence, we are able to sip hot tea or milk faster from a saucer. However, in a cup, the surface area is small, so evaporation occurs slowly and the liquid remains hot for a long time.
5) What type of clothes should we wear in summer?
Ans: We should wear white cotton clothes in summer. This is because cotton is a good observer of water and therefore, it helps in observing sweat from our body. It also exposes it to the atmosphere for easy evaporation. The evaporation of this wet cools our body. Therefore, our body feels cool.
Exercise
1) Convert the following temperature to celsius scale at
(a) 293K (b) 470 K
Ans: (a) 0c=0k-273=293-273=200c
(b) 0c=0k-273=293-470=1970c
2) Convert the following temperature is to the Kelvin scale is
(a) 25°C (b) 373°C
Ans: (a) 0k=0c+273=25+273=2980k
(b) 0k=0c+273=373+273=6460k
3) Give the reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
Ans: Naphthalene undergoes sublimation that is changes state from solid to gas directly hence it disappears.
(b) We can get the smell of perfume sitting several metres away.
Ans: Perfume particles enter mixes with the particles, that is it undergoes diffusion hence we can get the smell of the perfume sitting several metres away.
4) Arrange the following substances in increasing order of forces of attraction between the particles water, sugar, oxygen.
Ans: Oxygen, water, sugar
5) What is the physical state of water at –
(a)250c
(b) 00c
(c)1000c
Ans: 250c- liquid state
00c- solid state.
1000c-gaseous state
6) Give two reasons to justify
(a)water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
Ans: (a) as it has no fixed shape but take the shape of the container it has fixed volume
(b) It has a definite shape and district boundary it has fixed volume with Nick negligible compressibility.
7) Why is ice at 273K more effective in cooling than water at the same temperature?
Ans: The melting point of ice is 273K, it absorbs heat to melt but the temperature does not change, but water remains water at the same temperature hence ice is more effective in cooling.
8) What produces more severe burns, boiling water or steam?
Ans: Steam produces more severe burns than boiling water. Particles in steam have more energy than water at the same temperature as particles in steam have observed in extra energy in the form of latent heat of vaporisation.
9) Name A, B, C, D, E and F in the following diagram showing the change in its state.
Ans: A) fusion
B) vaporisation
C) condensation
D) solidification
E) sublimation
F) desublimation
B) vaporisation
C) condensation
D) solidification
E) sublimation
F) desublimation
Extra Questions
1) What is matter?
Ans: Substance which has mass and occupies space is known as matter.
2) Name three states of matter.
Solid, Liquid, Gas.
3) How do aquatic animals breathe?
Ans: The aquatic animals can breathe underwater due to the presence of dissolved oxygen in the water.
4) The rate of diffusion of liquid is higher than the hot of solids. Why?
Ans: The rate of diffusion of liquid is higher than that of solids due to the fact that in the liquid state, particles move freely and have greater space between each other as compared to particles in a solid-state.
5) Gases show the property of diffusing very fast into other gases why?
Ans: Due to the high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.
6) What is the pressure exerted by gas due to?
Ans: The pressure exerted by a gas is because of the force exerted by gas particles per unit area on the walls of the container.
7) Define the following
Melting point: The temperature at which solid melts to become a liquid at the atmospheric pressure is called its melting point.
Latent heat of fusion: The amount of heat energy that is required to change one KG of a solid into liquid at atmospheric pressure as its melting point is known as the latent heat of fusion.
Latent heat of vaporisation: The amount of heat energy that is required to change one KG of liquid into a gas at atmospheric pressure as its boiling point is known as the latent heat of vaporisation.
Boiling point: The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.
8) What are these
(a) Change of solid state into a liquid state
(b) A change of state directly from solid to gas without changing into the liquid state
(c) The phenomenon of change of a liquid into vapours at any temperature below its boiling
(d) Amount of water vapour present in the air
Ans: (a) Fusion
(b) Evaporation
(c) Sublimation
(d) Humidity
9) For any substance, why does the temperature remain constant during the change of state?
Ans: The heat provided to a substance gets used up in changing the state by overcoming the forces of attraction between the particles hence the temperature remained constant during the change of state.
(a) Change of solid state into a liquid state
(b) A change of state directly from solid to gas without changing into the liquid state
(c) The phenomenon of change of a liquid into vapours at any temperature below its boiling
(d) Amount of water vapour present in the air
Ans: (a) Fusion
(b) Evaporation
(c) Sublimation
(d) Humidity
9) For any substance, why does the temperature remain constant during the change of state?
Ans: The heat provided to a substance gets used up in changing the state by overcoming the forces of attraction between the particles hence the temperature remained constant during the change of state.
Important points
- Matter is made up of particles.
- The particles of matter are very smart will stop
- Particles of matter how space between them.
- Since particles of matter or continuously moving they possess kinetic energy.
- With the increase in temperature the kinetic energy of the particles also increases.
- Intermixing of particles of two different types of matter on their own is called diffusion.
- Particles of matter have a force acting between them will stop.
- The strength of the force of attraction between particles varies from one kind of matter to another please stop.
- The three different states of matter are solid, liquid and gas.
- Solids have definite size, shape and fix it volumes.
- Liquid do not have a definite size,they take the shape of the container but have fixed volume.
- Solid-liquid and gaseous can diffuse into liquid.
- Gases are highly compressible ash compressible solids and liquids.
- Rate of diffusion of liquid is higher than that of solids.
- The pressure exerted by the gases because of those extended by gas particles per unit area on the wall of the container.
- The mass per unit volume of a substance is called density.
- The temperature at which solid melts to become a liquid at the atmospheric pressure is called the melting point.
- The melting point of solid is an indication of the strength of the force of attraction between its particles.
- Change of solid state into a liquid state is known as Fusion.
- Change of liquid state to a solid-state is called solidification.
- Change of liquid state to the gaseous state is called
- Change of gaseous state to a liquid state is called condensation.
- Change of solid-state to gaseous state or gaseous state the solid-state is called sublimation.
- The amount of heat energy that is required to change one cagey of a solid into a liquid at atmospheric pressure at its melting point is known as the latent heat of Fusion.
- The temperature at which a liquid start boiling at the atmospheric pressure is known as its boiling point.
- The amount of heat energy that is required to change one cagey of liquid into a gas atmospheric pressure at its boiling point is known as latent heat of vaporization.
- The phenomenon of change of a liquid into wafers at any temperature below its boiling point is called evaporation.
- Evaporation causes cooling.
- Factors affecting operation:
->an increase of surface area.
->an increase of temperature.
->a decrease in humidity.
->an increase in wind speed will stop.
