I. Very short answer type questions:
1. Define latent heat.
Ans. Latent heat is the hidden heat that is required to convert the matter from one state to another state without a change in temperature.
2. Define sublimation and deposition.
Ans. Sublimation is the process by which solid on heating directly changes into the gaseous state without a change in a liquid state and vice versa.
Example- Iodin, camphor, naphthalene, dry ice, etc change directly into a gaseous state when they are heated.
Example- Iodin, camphor, naphthalene, dry ice, etc change directly into a gaseous state when they are heated.
Deposition: Deposition is the opposite process of sublimation. It involves the direct conversion of a gas to a solid without passing through the liquid state. During deposition, the gas loses energy and transitions directly into the solid state.
3. A sponge is a solid, yet we are able to compress it. Why?
Ans. A sponge is solid and has many small holes, in which air is trapped. When we press it, the air is expelled out and we are able to compress it.
4. Convert 373 C to the Kelvin.
Ans. Temp. In Kelvin = Temp. In Celsius + 273
For example - 373 C + 273 = 646 K
5. Latent heat of evaporation of two liquids A and B is 100 J/kg and 150 J/kg respectively. Which one can produce more cooling effect and why?
Ans. B can produce more cooling effect because it absorbs more heat energy per kg.
6. What happens to the melting point of solid with an increase in pressure?
Ans. In most cases, the melting point of substances increases with an increase in pressure. However, the melting point of ice decreases with an increase in pressure.
7. Name the state of matter that has minimum space between particles.
Ans. Solid-state has minimum space between particles.
8. Name the property of gas that helps aquatic plants and animals to survive in water?
Ans. Diffusion is the property of gases that helps aquatic animals and plants to survive in water. Respiratory gases oxygen and carbon dioxide diffuse in water and helps them to breathe in the water.
9. How can we liquefy gases?
Ans. When the pressure is increased on gas, the gas undergoes condensation that is it liquifies and changes into a liquid.
10. Which of the following is matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold drink, the smell of perfume.
Ans. Chair, air, almonds, cold drinks, the smell of perfume are the matter that occupies space, has mass and is realized by our senses. (Smell of perfume is matter but the smell is not a matter)
11. 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. Exhaust from chimney < air < cotton < water < honey < chalk < iron.
12. Are the three states of matter inter-convertible? How can they interconnect?
Ans - Yes, three states are interconvertible.
(a) When the solid matter is heated, it changes into the liquid and this phenomenon is called melting.
(b) When the liquid matter is heated, it changes into the gaseous state. This phenomenon is called evaporation.
(c) Gaseous state on cooling changes into the liquid state and this phenomenon is called condensation.
(a) When the solid matter is heated, it changes into the liquid and this phenomenon is called melting.
(b) When the liquid matter is heated, it changes into the gaseous state. This phenomenon is called evaporation.
(c) Gaseous state on cooling changes into the liquid state and this phenomenon is called condensation.
13. Define matter.
Ans. The matter is defined as one which occupies space, has mass and is realized by our sense. Matters may be solid, liquid or gas.
14. Write the full form of LPG and CNG.
Ans. Full form of LPG - Liquefied petroleum gas
Full form of CNG - Compressed natural gas.
15. Write the two factors that determine the rate of diffusion.
Ans. Two factors that determine the rate of diffusion are:
(a) Temperature - Diffusion increases with an increase in temperature.
(b) Density - Diffusion increases with a decrease in density.
16. What is the SI unit of volume?
Ans. S.I unit of volume is the cubic meter.
17. Fill in the blanks: 1l = _____ ml, 1 ml = ________cm^3.
Ans. 1l =1000 ml and 1ml = 1000 cm^3.
18. Define fusion.
Ans. Solid-state on heating changes into a liquid state. This phenomenon is called fusion.
19. What is the unit of measuring the pressure exerted by a gas?
Ans. Gas pressure may be measured by the unit of mmHg or Pascals.
20. Define atmospheric pressure.
Ans. The pressure of air in the atmosphere is called atmospheric pressure.
21. What is the atmospheric pressure at sea level?
Ans. 760 mm of Hg or 76 cm of Hg.
22. What does the melting point of a solid indicate?
(b) Density - Diffusion increases with a decrease in density.
16. What is the SI unit of volume?
Ans. S.I unit of volume is the cubic meter.
17. Fill in the blanks: 1l = _____ ml, 1 ml = ________cm^3.
Ans. 1l =1000 ml and 1ml = 1000 cm^3.
18. Define fusion.
Ans. Solid-state on heating changes into a liquid state. This phenomenon is called fusion.
19. What is the unit of measuring the pressure exerted by a gas?
Ans. Gas pressure may be measured by the unit of mmHg or Pascals.
20. Define atmospheric pressure.
Ans. The pressure of air in the atmosphere is called atmospheric pressure.
21. What is the atmospheric pressure at sea level?
Ans. 760 mm of Hg or 76 cm of Hg.
22. What does the melting point of a solid indicate?
Ans. The melting point of a solid is a fixed temperature at which a solid changes into a liquid state and it indicates the strength of the force of attraction between the particles of the solid.
23. What is dry ice?
Ans. Solid carbon dioxide is called dry ice. It is used as a cooling agent.
Carbon dioxide gas is first pressurized and cooled to form liquid CO2 and once released to atmospheric pressure, the liquid carbon dioxide converts to dry ice and CO2(g).
24. What is frosting?
And. Conversion of gas to solid directly without changing into liquid is called frosting.
25. Write an expression for the relation between celsius C and Fahrenheit F.
Ans. 9/5 C = F - 32
26. 1 atmosphere = _____________ Pa..
And. 101325 Pa
23. What is dry ice?
Ans. Solid carbon dioxide is called dry ice. It is used as a cooling agent.
Carbon dioxide gas is first pressurized and cooled to form liquid CO2 and once released to atmospheric pressure, the liquid carbon dioxide converts to dry ice and CO2(g).
24. What is frosting?
And. Conversion of gas to solid directly without changing into liquid is called frosting.
25. Write an expression for the relation between celsius C and Fahrenheit F.
Ans. 9/5 C = F - 32
26. 1 atmosphere = _____________ Pa..
And. 101325 Pa
27. Why is boiling a bulk phenomenon?
Ans. Boiling is a bulk phenomenon. Particles of the liquid gain enough energy to change to a vapour state. The entire liquid and all the molecules including the interior and the surface gain energy to change to a vapour state.
II. Short answer type questions:
1. Explain why heat energy is needed to melt a solid?
Ans. In a solid intermolecular force between the particles is very strong so heat energy is essential to overcome the intermolecular force.
2. Explain the state of matter on the basis of kinetic theory.
Ans. State of matter on the basis kinetic theory:
(i) When the intermolecular forces between the particles are strong, particles come closer and occupy solid state.
(ii) When the intermolecular force between the particles is weak, particles stay far apart from one another and occupy either liquid or gaseous state.
3. Write the S.I units of the followings:
(i) Mass (ii) Length ( iii) Temperature (iv) Force (v) Volume (v)Density (v)Pressure.
Ans. (i) Mass ----- Kg ( Kilogram)
(ii) Length ---- m
(iv) Temperature --- K ( Kelvin)
(v) Force -- N (Newton)
(vi) Volume --- m3( Cubic meter)
(v) Density --- Kg/m3
(vi) Pressure -- Pa ( Pascal)
4. Give reasons for the following observation: The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.
Ans. The rate of evaporation, kinetic energy and diffusion increases with the rise in temperature. Thus the smell of hot sizzling food reaches us from several meters away.
The rate of evaporation, kinetic energy, and diffusion of cold food, comparatively less than hot food. So cold food realized only on coming closer.
5. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Ans. A diver is able to cut through water in a swimming pool because of a weak intermolecular force of attraction between water molecules. The diver used streamlines action to reduce this force.
6. What are the characteristics of the particles of matter?
Ans. (i) Matter in either of the state (solid, liquid or gas) is composed of very small particles of molecules or atoms or ions.
(ii) The constituent particles, atoms, molecules or ions have space between them.
(iii) The particle of matter is held together by intermolecular force.
(iv) Particles of matter are always in a state of motion.
(v) Particles of matter possess kinetic and potential energy.
7. State the form of energy possessed by particles of matter in motion? How does the increase in temperature affect the rate of diffusion?
Ans. Kinetic energy is possessed by particles of matter in motion. When the temperature is increased, kinetic energy increases and the rate of movement of particles also increases. The higher the temperature, the higher the kinetic energy and the faster the rate of diffusion.
8. Define the kinetic theory of matter.
Ans. The theory which visualizes that any substance whether solid liquid or gas is made up of tiny particles atoms molecules or ions which are in constant motion is called the Kinetic theory of Matter.
9. Define the latent heat of vaporization and latent heat of fusion.
Ans. The latent heat of vaporization is the quantity of heat in joules required to convert 1 kg of liquid to vapour or gas without a change in temperature.
The latent heat of fusion is the quantity of heat in joules required to convert 1 kg of solid to liquid without a change in temperature.
10. Why should we wear cotton clothes in summer?
Ans. Because cotton cloths are a good absorber of water, so in summer it absorbs sweat from our body and evaporates it into the atmosphere by absorbing heat from our body and the heat of the body gets dissipated during evaporation of sweat and keeps us cool.
11. Write the two differences between gas and vapour?
Ans.
Ans.
Vapour
i. A substance which under ordinary temperature is a solid or liquid, but under specific conditions is gaseous, is called vapour.
ii. It is a substance above its boiling point temperature.
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Gas
i. Gas is a substance above its critical temperature but below its critical pressure.
ii.It a substance which exists in the
gaseous state under ordinary conditions.
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12. What happens when the temperature of the solids increase?
Ans. When the temperature of the solid is increased, the supplied heat absorbed by the constituent particles and therefore the kinetic energy of the constituent particles increases. Due to this intermolecular force of attraction decreases and inter-molecular space increases, thus solid starts changing into a liquid state.
13. When heat is being supplied to a solid, then what does the heat energy do to the particles of solid?
Ans. When heat is being supplied to a solid, then the heat energy increases the kinetic energy of the particles of solid and the particles start vibrating more vigorously leading to the weakening of interparticle forces.
14. Why is it that on increasing the wind speed the rate of evaporation increases?
Ans. With the increase in wind speed, the particles of water vapour move away with the wind, decreasing the amount of water vapour in the surrounding. Hence evaporation increases.
15. Why do we say that evaporation is a surface phenomenon?
Ans. The particles of the surface of liquids which are in contact with surroundings, gain heat energy from surroundings and its kinetic energy increases, due to these particles of the surface of water evaporate. So evaporation takes place at the surface of a liquid and we say that evaporation is a surface phenomenon.
16. Why is it that a wooden chair should be called a solid and not a liquid?
Ans. Because a wooden chair like solid, have least, and fixed inter-particle space between their molecules, constituent particles are closely packed and can vibrate about a fixed axis.
While in liquids they have more inter-particle space between their molecules than solid, constituent particles are loosely packed and free to move in such a way that they remain in contact with one another. So a wooden chair is called a solid.
While in liquids they have more inter-particle space between their molecules than solid, constituent particles are loosely packed and free to move in such a way that they remain in contact with one another. So a wooden chair is called a solid.
17. How does evaporation cause cooling?
Ans. Evaporation requires heat energy. The particles of surface liquid absorb this heat energy from its surroundings during evaporation and thus temperature is lowered and one feels cool.
18. Why does our palm feel cold when we put some acetone or petrol or petroleum on it.
Ans. Due to evaporation of low boiling point liquids that is acetone by absorbing the heat from our palm.
19. Why does the water kept in an earthen pot becomes cool during summer?
Ans. In summer the temperature is more and evaporation becomes faster. The earthen pots are porous and allow the tiny water particles to get evaporated. The heat required for evaporation is supplied by water kept in the pot. So
20. Why does a desert cooler cool better on a hot dry day?
Ans. On a hot dry day, the temperature is more and humidity is low due to which the rate of evaporation of water becomes faster. Due to the increase in the rate of evaporation more water gets vaporized and cooling is better.
21. Explain the interconversion of three states of matter with the help of a chart or diagram. Name the process of each conversion.
Ans.
(i) Solid to Liquid: Fusion
(ii) Liquid to Gas: Vaporization
(iii) Gas to liquid: Condensation
(iv) Liquid to Solid: Solidification
(v) Solid to Gas: Sublimation
(vi) Gas to Solid: Frosting
22. Discuss the various factors affect the rate of evaporation.
Ans. Factors affect the rate of evaporation:
I. Temperature- Evaporation increases with an increase in temperature.
ii. Humidity - Evaporation increases with a decrease in humidity
iii. Wind speed- Evaporation increases with an increase in wind speed.
iii. Wind speed- Evaporation increases with an increase in wind speed.
iv. Surface area-Evaporation increases with an increase in surface area.
23. How does pressure help in liquefaction of gas? Name two liquefied gases used in daily life.
Ans. When the pressure has increased the result of having more molecules in a certain volume. This means that the average distances between molecules are shorter and intermolecular forces get stronger, which is the key to the formation of a liquid.
24. Gases are more compressible, write two reasons for this.
Ans. Force of attraction between molecules of gases is negligible due to which intermolecular space is maximum than solid and liquid. That is why gases are more compressible.
25. If the boiling points of oxygen, argon, and nitrogen are -182C, -186C and -196C
(a) Which gas forms the liquid first as the air is cooled?
(b) Which gas is obtained first when liquid air boils up?
Ans. (a) Oxygen forms the liquid first as the air is cooled.
(b) Nitrogen obtained first when liquid air boils up as it has the lowest boiling point.
26. Why do we see water droplets on the outer surface of a glass containing ice-cold water?
Ans. The water vapour present in the atmosphere, on coming in contact with the cold glass of water and condense into water droplets (in liquid state).
27. During the summer, we perspire more. Why?
And. In summers temperature of the outside is more than our body temperature so to get equilibrium our body temperature starts increasing so as to cool our body sweat glands produce sweat so that it can evaporate and take the heat of our body hence cooling.
28. When we dissolve salt in water, the level of water does not change. Why?
Ans. When we dissolve salt in water, the level of water does not change because the particles of water are loosely packed and having space between them which is known as intermolecular space. This intermolecular space accommodates the salt particles.
29. The melting point of sodium and potassium are 370K and 336K. What information it can provide?
Ans. The melting point of sodium is greater than potassium. It means the interparticle force is stronger and interparticle distance or space is less in sodium.
30. Water boils below 100 degrees C at the mountain. Explain.
Ans. Water boils when its vapour pressure becomes equal to the atmospheric pressure which is 76 cm of Hg. Atmospheric pressure at the mountain is less than 76 cm of Hg. So water boils below 100 degrees C at the mountain.
31. The heat energy is more in steam than in water at 100 degrees C or 373 K (100C + 273). Why?
Ans. Particles in steam, that is, water vapour at 373 K (100 C) have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporization.
32. The heat energy is more in the water at 0 degrees C or 273 as compared to particles in ice at the same temperature. Why?
Ans. particles in water at 0 C (273 K) have more energy as compared to particles in ice at the same temperature because particles in water have absorbed extra energy in the form of latent heat of fusion.
33. Convert the following temperatures to the Kelvin scale:
(a) 35 degree C (b) 273 degree C.
Ans. (a) 35 degree C - 35 + 273 = 308 k
(b) 273 degree C - 273 + 273 = 546 k
34. Convert the following temperatures to the Celsius scale:
(a) 400 k (b) 673 k.
Ans. (a) 400 k = 400 - 273 = 127 C
(b) 673 k = 673 - 273 = 400 C
26. Why do we see water droplets on the outer surface of a glass containing ice-cold water?
Ans. The water vapour present in the atmosphere, on coming in contact with the cold glass of water and condense into water droplets (in liquid state).
27. During the summer, we perspire more. Why?
And. In summers temperature of the outside is more than our body temperature so to get equilibrium our body temperature starts increasing so as to cool our body sweat glands produce sweat so that it can evaporate and take the heat of our body hence cooling.
28. When we dissolve salt in water, the level of water does not change. Why?
Ans. When we dissolve salt in water, the level of water does not change because the particles of water are loosely packed and having space between them which is known as intermolecular space. This intermolecular space accommodates the salt particles.
29. The melting point of sodium and potassium are 370K and 336K. What information it can provide?
Ans. The melting point of sodium is greater than potassium. It means the interparticle force is stronger and interparticle distance or space is less in sodium.
30. Water boils below 100 degrees C at the mountain. Explain.
Ans. Water boils when its vapour pressure becomes equal to the atmospheric pressure which is 76 cm of Hg. Atmospheric pressure at the mountain is less than 76 cm of Hg. So water boils below 100 degrees C at the mountain.
31. The heat energy is more in steam than in water at 100 degrees C or 373 K (100C + 273). Why?
Ans. Particles in steam, that is, water vapour at 373 K (100 C) have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporization.
32. The heat energy is more in the water at 0 degrees C or 273 as compared to particles in ice at the same temperature. Why?
Ans. particles in water at 0 C (273 K) have more energy as compared to particles in ice at the same temperature because particles in water have absorbed extra energy in the form of latent heat of fusion.
33. Convert the following temperatures to the Kelvin scale:
(a) 35 degree C (b) 273 degree C.
Ans. (a) 35 degree C - 35 + 273 = 308 k
(b) 273 degree C - 273 + 273 = 546 k
34. Convert the following temperatures to the Celsius scale:
(a) 400 k (b) 673 k.
Ans. (a) 400 k = 400 - 273 = 127 C
(b) 673 k = 673 - 273 = 400 C
35. Why does the temperature of a system does not change after melting point of reached?
Ans. When a substance undergoes a change of state, such as melting or boiling, the temperature of the system remains constant until the entire substance has completed the phase transition. This phenomenon is known as a phase transition plateau or plateau region. Here's why the temperature doesn't change during this transition.
III. Long answer type questions:
1. Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.
Ans. Rigidity- It is the property of matter to resist the change in shape
Compressibility-It is the property of matter in which its volume decreased by applying force.
Fluidity - Gas can flow freely in any direction due to the presence of weak
Intermolecular forces between particles.
Filling a gas container- On filling a gas takes the shape of the container.
Shape- Having definite shapes.
Kinetic energy- It is the energy possessed by the particles of matter due to its motion.
Density - Ratio of mass to the volume.
2. Tabulate the differences in the characteristics of states of matter.
Ans. (i) Solid - The constituent particles are tightly packed.
Liquid- The constituent particles are loosely packed.
Gas - There is no definite arrangement in particles.
(ii) Solid - Interparticle distance is fixed and is very small.
Liquid - Inter-molecular space is small but greater than solid.
Gas - Intermolecular space is very large compared to the solid and liquid.
(iv) Solid - Have definite shape, sizes, and volume.
Liquid - Have no definite shape, but have a definite volume.
Gas - Have no definite shape, definite volume and size, it acquires the shape of containers.
(v) Solids are very less compressible.
Liquids are less compressible but more than solid.
Gases are highly compressible due to the presence of a very large space between the molecules.
3. Give reasons:
(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 gas are free to move in any direction due to very weak inter-particle force which is negligible, That is why a gas fills completely the vessel in which it is kept in
(b) Since the particles of a gas are free to move in all the possible direction, they strike the walls of the container with a definite force per unit area and exert a definite force under a given set of conditions to develop pressure.
(c) In a wooden table, the constituent particles are unable to exert translational motion because they are held together by strong cohesive forces due to which wood has definite shape, volume, and size. Therefor a wooden table is called a solid.
(d) The constituent particles of wood which is solid held together by strong intermolecular force, the movement of hand through a solid block of wood , therefore, require a large amount of energy to separate the particles so only a karate expert is able to exert such a large force and is able to do so.
4. Give reasons for the following taking into evaporation:
(a) While putting clothes for drying up we spread them out.
(b) Clothes dry up faster when spread near a heater.
(c) Clothes take a very long time to dry on a rainy day.
Ans. (a) Spreading the cloths for drying increases the surface area which helps it to dry faster as the rate of evaporation increases with an increase in area.
(b) Clothes dry up faster when spread near a heater because the heater increases the temperature which helps it to dry faster as the rate of evaporation increases with an increase in temperature.
(c) Clothes take a very long time to dry on a rainy day because the rate of evaporation decreases with an increase in humidity.
5. Carbon dioxide was taken in an enclosed cylinder and compressed by applying pressure.
(a) Which state of matter will be obtained after completion of the process?
(b) Name and define this process.
(c) What is the common name of the product obtained in the above process?
Ans. (a) In solid-state.
(b) Sublimation: This is the process in which gas direct changes into solid-state vice versa.
(c) Dry Ice - It is solid carbon dioxide.
6. What is the effect of a change of pressure on the physical state of matter? Explain with an example of a gas.
Ans. Pressure plays a very important role in changing the physical state of matter. The distance between constituent particles of matter can be changed by increasing or decreasing pressure on it. Thus the interconversion of the states of matter can be affected by a change in pressure.
Example: Solid carbon dioxide called dry ice, is stored under high pressure.
If the pressure is decreased it would change from solid to a gaseous state.
7. What is the effect of the increase in temperature on the solid-state of matter? Explain.
Ans. When temperature increases heat energy of solid increases, due to this kinetic energy of particles also increases and the intermolecular force of attraction decreases. Thus the particles of matter become free to move and the solid starts changing into the liquid or gaseous state.
8. Name two processes that illustrate that on heating, movement of particles of matter increases. Define fluidity. Explain why liquids flow.
Ans.Two processes which illustrate that on heating, movement of particles of matter increases are:
(a) Diffusion - The rate of diffusion increases on heating because when the temperature of a substance is increased by heating, its particle gains kinetic energy and move more rapidly.
(b) Brownian motion. The rapid and zig-zag movement of tiny particles in a liquid is called Brownian motion. This motion increases on heating because the movement of tiny particles gain kinetic energy and move faster.
9.(i) Convert the following temperature to Celsius scale:
(a) 300 K (b) 573 K.
(ii) What is the physical state of water at:
(a) 250ºC (b) 100ºC ?
(iii) For any substance, why does the temperature remain constant during the change of state?
(iv) Suggest a method to liquefy atmospheric gases.
Ans.(i) (a)Temperature on Celsius = Temperature on Kelvin - 273.
Temperature in Celsius = 300K - 273 = 27oC
(b) Temperature in Celsius = 573K - 273 = 300oC
(ii) a. Gas, b. Steam.
(iii) During inter-conversion of state of a substance, the heat supplied or withdrawal is utilized in overcoming or restoring the inter-particle force of attraction. Thus no increase in temperature is recorded. This heat involves or absorbs is termed as the latent heat.
(iv) Atmospheric gases can be liquefied by lowering the temperature than its critical temperature and increasing the pressure.
10. Give reason after a hot sunny day people sprinkle water on the roof or open ground.
Ans. After a hot sunny day roof and the open ground becomes hot. When people sprinkle water, it evaporates and leads to a decrease in temperature because water takes heat from the floor and ground for evaporation.
10. Give reason after a hot sunny day people sprinkle water on the roof or open ground.
Ans. After a hot sunny day roof and the open ground becomes hot. When people sprinkle water, it evaporates and leads to a decrease in temperature because water takes heat from the floor and ground for evaporation.
11. State the reasons for the following:
(a) The smell of lighted incense stick reaches you several meters away, but to get the smell from until incense stick you have to go close.
(b) The naphthalene balls disappear with time without leaving any solid.
Ans. The rate of evaporation, kinetic energy and diffusion increases with the rise in temperature. Thus the smell of lighted incense stick reaches us from several meters away.
The rate of evaporation, kinetic energy, and diffusion of until incense stick, comparatively less than lighted incense stick. So until incense stick realized only on coming closer.
(b) Naphthalene balls are the sublime substances, so the naphthalene balls disappear with time without leaving any solid, in which substances are directly changed into the gaseous state without a change in liquid.
12. The rate of diffusion is faster in gas. Why?
Ans Because :
i. Force of attraction between molecules of gases is negligible due to which particles can move freely.
ii. The kinetic energy of particles of gas is more than solids and liquids.
That is why the rate of diffusion is faster in gas.
13. Why gases exert pressure on the walls of containers?
Ans. Force of attraction between molecules of gases is negligible due to which particles of gases can move randomly in all directions. During the motion, they collide with each other and also with the walls of the container.
14. Write any three differences between evaporation and boiling.
Ans. Three differences between evaporation and boiling are:
(a) Evaporation occurs at any temperature, but boiling occurs only at boiling points.
(b) Evaporation produces a cooling effect, but boiling produces a heating effect.
(c) It is a surface phenomenon, but boiling is a bulk phenomenon (whole part of the liquid)
15. The temperature-time graph given below shows the heating curve for pure wax. After studying the graph answer the following questions:
(a) What is the physical state of a substance at points A, B, C, and D?
(b) What is the melting point of the substance?
(c) What is its boiling point?
(d) Which portions of the graph indicate that change of state is taking place?
Ans. (a) A - Solid-state B - Fusion C - Liquid D - Vapourisation.
(b) At A1- the melting point is 150C
(c) At D1 - the boiling point is 1100C
(d) A1B1 and D1D2
Latent heat of fusion and latent heat of vaporization
16. How can we obtain different gases from the air? Draw the flow diagram to show the state of the process.
Ans. We may obtain different gases from air by the process of liquefaction by applying pressure and lowering the temperature.
Flow diagram :
17. What are the characteristics of Particles of Matter?
(a) Can a rubber band it change its shape on stretching? Is it solid?
(b) When sugar and salts are kept in different jars these take the shape of the jar. Are they solid?
Ans. The particles of matter:
i. are very very small.
ii. have space between them.
iii. are constantly moving.
iv. attract each other.
(a) A rubber band changes its shape on stretching under force and regains the same shape when the force is removed. It is solid.
(b) When sugar and salts are kept in different jars these take the shape of the jar but the shape of each individual sugar or salt crystal remains fixed, whether we take it in our hand, put it in a plate or in a jar. So they are solid.
18. The rate of diffusion of liquids is higher than that of solids. Why?
Ans. In the liquid state, the force of attraction between the constituent particles is less than solid, particles move freely and have greater space between each other as compared to particles in the solid-state. So the rate of diffusion of liquids is higher than that of solids.
19. What happens to the particles of matter during the change of states?
Ans. When the temperature of solids increases, the kinetic energy of the particles increases, and the particles start vibrating with more 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. After a fixed stage the solid starts melting and converted into a liquid.
20. Explain about the Bose-Einstein Condensate and plasma state of matter.
Ans. Plasma: The plasma is the fourth state of matter consists of super energetic and super excited particles in the form of ionized gases. In the fluorescent tube and neon sign bulbs neon gas and helium gas or some other gases get ionized when electrical energy flows through it. This ionized gas creates a plasma glowing inside the tube or bulb. The plasma glows with a special colour and depends on the nature of the gas. The Sun and the stars glow due to the presence of plasma in them. The plasma is created in stars due to very high temperatures.
Bose-Einstein Condensate: The BEC is formed by cooling a gas of extremely low density, about one-hundred-thousandth the density of normal air, to super-low temperatures. It was predicted by Albert Einstein in 2001, Eric A.
21. Why the interconversion of the state of matter is considered as a physical change? Give three reasons to justify your answer.
Ans. The interconversion of the state of matter is considered as a physical change as:
i. there is no change in the chemical properties of the matter.
ii. no new substance is formed, the substance remains the same in the different states.
iii. it is a reversible change, a substance can back to its original state by physical means.
NCERT QUESTIONS:
- Which of the following is matter? Chair, air, love, smell, hate, almonds, thought, cold, cold drink, the smell of perfume.
- Give reasons for the following observation: The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.
- A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
- What are the characteristics of the particles of matter?
- 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.
- (a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density. - Give reasons:
(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. - Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
- Convert the following temperature to Celsius scale: (a) 300 K, (b) 573 K.
- What is the physical state of water at a. 250ºC b. 100ºC?
- For any substance, why does the temperature remain constant during the change of state?
- Suggest a method to liquefy atmospheric gases.
- Why does a desert cooler cool better on a hot dry day?
- How does the water keep in an earthen pot (matka) become cool during summer?
- Why does our palm feel cold when we put some acetone or petrol or perfume on it?
- Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
- What type of clothes should we wear in summer?
- Convert the following temperatures to the Celsius scale. (a) 300 K (b) 573 K.
- Convert the following temperatures to the Kelvin scale. (a) 25°C (b) 373°C.
- Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several meters away. - Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.
- What is the physical state of water at— (a) 25°C (b) 0°C (c) 100°C?
- Give two reasons to justify—
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature. - Why is ice at 273 K more effective in cooling than water at the same temperature?
- What produces more severe burns, boiling water or steam?
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