Lakhmir Singh Manjit Kaur Class 9 Science 1st Chapter “Matter In Our Surroundings” Part-II solution

Lakhmir Singh Manjit Kaur Class 9 Science 1st Chapter “Matter In Our Surroundings” Part-II solution

Very Short Answer Type Questions

(1) The boiling point of water is 100o C. Express this in SI units (Kelvin scale)

Ans. 373 K

(2) The Kelvin temperature is 270K. What is the corresponding Celsius scale temperature?

Ans. -3o C

(3) Convert the temperature of 573 K to the Celsius scale.

Ans. 300 degree celsius.

(4) Convert the temperature of 3730 celsius to the Kelvin scale.

Ans. 646 K

(5) The boiling point of Alcohol is 780 Celsius, What is the temperature of Kelvin scale?

Ans. 351 K

(6) The Kelvin scale temperature is 0 K. What is the corresponding Celsius scale temperature.

Ans. – 273 degree celsius.

(7) Give the usual name for the following:

Heat required to change the state of a substance of a substance without changing the temperature.

Ans. Latent heat.

(8) What is the (a) common unit of temperature, and (b) SI unit of temperature

Ans. (a) O0 C

(b) Kelvin

(9) Write the relation between Kelvin scale and celsius scale of temperature.

Ans. Temp. on Kelvin scale = Temp. on Celsius scale + 273

(10) What should be added to a Celsius scale reading so as to obtain the corresponding Kelvin scale reading?

Ans. 273

(11) What is meant by saying that the latent heat of fusion of ice is 3.34 x 105 J/kg

Ans. The latent heat of fusion of a solid is the quantity of heat in joules required to convert 1 kilogram of the solid to liquid, without any change in temperature. It has been found by experiments that 3.34 x 105  joules of heat has to be supplied to change 1 kilogram of ice to water at the same temperature of Oo C, So the latent heat of fusion of ice is 3.34 x 105 J/kg.

(12) What is meant by saying that the latent heat of vaporisation of water is 22.5 x 105 J/kg?

Ans. It has been found in experiment that 22.5 x 105 joules of heat is required to change 1 kilogram of water (at its boiling point, 100o C) to steam at the same temperature of 100o C. So the latent heat of vapourisation of water is 22.5 x 105 J per kilogram.

(13) Name the temperature at which (a) a liquid changes into a gas (b) a solid changes into a liquid.

Ans. (a) Boiling point

(b) Heating point.

(14) Name one common substance which can be easily changed from one state to another by heating cooling,

Ans, Water

(15) What is the name of the process in which

(a) a solid turns directly into gas (b) a gas turns directly into a solid.

Ans. (a) Sublimation

(b) Sublimation

(16) Name one property  which is shown by ammonium chloride but not by sodium chloride.

Ans. Sublimation.

(17) What is the name of the process due to which dry ice changes into carbon di oxide gas?

Ans. Comperation.

(18) What is the common name of Solid Carbon Di Oxide?

Ans. Dry Ice.

(19) Why is solid carbon do oxide known as dry ice?

Ans. Solid carbon di oxide directly changes into carbon di oxide gas and does not melt to produce a liquid, it is called dry ice. Dry ice can produce much lower temperatures than that produced by ordinary ice. So it is much more effective for cooling purposes than ordinary ice.

(20) State one condition necessary to liquefy gases (other than applying high pressure).

Ans. Lowering of temperature.

(21) State whether the following statement is true or false.

Solid Carbon Di Oxide is stored under low pressure. (False)

(22) What is the chemical name of dry ice?

Ans. Solid Carbon dioxide.

(23) Fill in the following blanks with suitable words:

(a) Pressure; Temperature.

(b) released

(c) 273

(d) Plasma; Bose-Einstein Condensate (BEC)

(e) Plasma.

Short Answer Type Questions:

 (24) What do you understand by the term ‘latent heat’? What are the two types of latent heat?

Ans. The heat energy which has to be supplied to change the state of a substance is called its latent heat.

Latent heat is of two types –

(i) Latent heat of fusion.

(ii) Latent heat of vapourisation.

(25) Why is heat energy needed to melt a solid? Why is this heat energy called?

Ans. When a solid is heated, the heat energy makes its particles vibrate more vigorously. At the melting point, the particles of solid have sufficient energy to overcome the strong forces of attraction holding them in fixed positions and break to form small groups of particles.

This heat energy is kinetic energy.

(26) Under what condition heat can be given to a substance without raising its temperature?

Ans. The heat which is going into solid but not increasing its temperature, is the energy required to change the state of solid from solid to liquid.

(27) Why does the temperature remain constant during the melting of ice even though heat is supplied continuously.

Ans. This is because of the latent heat of fusion.

(28) Why does the temperature remain constant during the boiling of water even though heat is supplied continuously?

Ans. This is because of latent heat of vapourisation.

(29) Explain why ice at OoC is more effective in cooling than water at the same temperature.

Ans. Ice at OoC is more effective in cooling a substance than water at OoC. This is due to the fact that for melting, each kilogram of ice takes its latent heat of 3.34×105 joules from the substance and hence cools the substance more effectively. On the other hand, water at OoC cannot take any such latent heat from the substance.

(30) Would you cool a bucket of water more quickly by placing it on ice or by placing ice in it? Give reason for your answer.

Ans. We would place ice in the water to cool it more quickly because the ice takes its latent heat from the water and hence cools it more effectively. On the other hand, if we keep the water on ice then the latent heat would be taken from the surrounding air hence releasing its coolness to the surrounding and not the water.

(31) Why does steam cause more severe burns than boiling water?

Ans. This is because steam has more heat energy than water due to its latent heat vaporization.

(32) Which contains more heat, 1 kg of ice at Oo C or 1 kg of water at Oo C? Give reason.

Ans. The latent heat of fusion of ice is 3.34 x 105 J/Kg. It means that 3.34x 105 joules of heat is required to change 1 Kg of ice at its melting point of 0oC into water at the same temperature (of 0oC). This means that 1 Kg of ice at 0oC has 3.34 x 105 joules of less heat than 1 kg of water at the same temperature of 0oC.

(33) Which contains more heat , 1 kg of water at 100o C or 1 kg of steam at 100oC? Give reason.

Ans. 1 Kg of steam at 100 degree Celsius has more heat than water at the same temperature because when water changes into steam, it absorbs latent heat, but when steam condenses to form water, an equal amount of latent heat is given out.

(34) Explain why, steam at 100o Celsius is better for heating purposes than boiling water at 100oC.

Ans. This is because of the fact that steam at 100oC contains more heat, in the form of latent heat, than boiling water at 100oC. Hence, steam would give out 22.5 x 105 joules per kilogram more heat than boiling water.

(35) Which produces more severe burns: boiling water or steam? Why?

Ans. Steam. This is because the steam contains more heat, in the form of latent heat, than boiling water. Hence, when steam falls on our skin and condenses to produce water it gives out 22.5 x 105 joules per kilogram more heat than boiling water.

(36) Why does the temperature of a substance remain constant during the change of state?

Ans. It is because the heat gets used up in changing the state by overcoming the forces of attraction between the particles.

(37) What is the physical state of water:

(a) at 0 degree celsius?

(b) at 25 degree celsius?

(c) at 100 degree celsius?

(d) at 250 degree celsius?

Ans. (a) Either solid (as ice) or liquid as 0oC is the melting point of ice as well as the freezing point of water.
(b) Liquid.
(c) Either a liquid or a gas (steam) as 100oC is the boiling point of water as well as the condensation temperature of steam.
(d) Gas.

(38) Explain why there is no rise in temperature of a substance when it undergoes a change of state though heat is supplied continuously.

Ans. The temperature of a substance remains constant during the change of state though heat is supplied continuously because the heat gets used up in changing the state by overcoming the forces of attraction between the particles.

(39) Define melting point of a substance? What is the melting point of ice?

Ans. The temperature at which the solid substance melts and changes into a liquid at atmospheric pressure is called the melting pint of the substance.

The melting point of ice is 0oC

(40) Define boiling point of a substance? What is the boiling point of water?

Ans. The temperature at which a liquid boils and changes rapidly into a gas at atmosphere pressure is called boiling point of the liquid.

The boiling point of water is 100 degree celsius.

(41) Define the following terms:

(a) Melting

(b) Boiling

Ans. (a) The process in which a solid substances changes into a liquid on heating is called Melting.

(b) The process in which a liquid substance changes into a gas rapidly  on heating is called boiling.

(42) Define the following terms:

(a) Condensation

(b) Freezing

Ans. (a) Condensation: The process of changing a gas (or vapour) to a liquid by cooling is called condensation..

(b) Freezing: The process of changing a liquid into a solid by cooling is called freezing.

(43) Explain why naphthalene balls kept in stored clothes in our in our homes disappear over a period of time.

Ans. It is because of sublimation naphthalene balls kept in stored clothes in our in our homes disappear over a period of time.

(44) Explain briefly how gases can be liquefied.

Ans. There is a lot of space between the particles of gas. We can reduce the spaces between the particles of a gas by enclosing it in a cylinder and compressing it by pushing in the piston. If enough force is applied to the piston, the gas is highly compressed. The particles of gas get so close together that they start attracting each other sufficiently to form a liquid. And we say that gas has liquefied. When a gas is compressed too much, then heat is produced due to compression. So while applying pressure to liquefy gases, it is necessary to cool them to take away the heat produced during compression. Cooling lowers the temperature of compressed gas and help in liquefying it.

(45) How is ammonia gas liquefied?

Ans. Ammonia gas can be liquefied by applying high pressure and lowering the temperature.

(46) How does applying pressure (or compression) help in the liquefaction of a gas?

Ans. There is a lot of space between the particles of a gas. If enough pressure is applied to the gas, it gets highly compressed. The particles of gas get so close together that they start attracting each other sufficiently to form a liquid. And we say that the gas has liquefied.

(47) How does perspiration or sweating help keep our body cool on a hot day?

Ans. Perspiration (or sweating) is our body’s method. Of maintaining a constant temperature. On a hot day or after doing some physical exercise, when our body temperature tends to rise too much, our sweat glands give out moisture on our skin. When this sweat evaporates it takes the latent heat of vaporization from our body. This keeps our body cool.

(48) Why does all the water of the earth not get evaporated during hot summer days?

Ans, This is because of the high value of latent heat of vaporization of water.

(49) If the back of your hand is moistened with alcohol, you will find that it rapidly becomes dry. Why is it that while it is drying , your hands feels cool.

Ans. If the back of our hand is moistened with alcohol we will see it is rapidly drying and gets cool due to the fact that to change from the liquid to the vapour state, alcohol requires latent heat of vaporization. The alcohol takes this latent heat of vaporization from our hand. The hand loses heat and gets cool.

(52) What type of clothes should we wear in summer? Why?

Ans. We should wear cotton clothes in hot summer days to keep cool and comfortable.

We get a lot of sweat on our body in hot summer days. Now cotton is a good absorber of water, so it absorbs the sweat from our body and exposes it to the air for evaporation.

(53) Why we are able to sip hot tea or milk hot tea or milk faster from a saucer rather than from a cup?

Ans. We are able to sip hot tea or milk faster from a saucer rather than from a cup because saucer has a large surface area. Due to the large surface of saucer, the evaporation of hot tea (or milk) from the saucer is faster. And this faster evaporation cools the hot tea (or milk) more quickly making it convenient for us to drink it.

(54) Why does our palm feel cool when we put some acetone (or perfume) on it?

Ans. If we put a little perfume at the palm of our hand and wave it around, the spirits evaporates rapidly and our hand feels very cool. This is due to the fact that no change from the liquid to the vapour state, perfume requires latent heat of vaporization from anything which it touches. By losing heat, this anything gets cooled.

(55) How will you demonstrate that water vapour is present in air?

Ans. The formation of drops of water on the outside surface of tumbler containing crushed ice shows the presence of water vapour in air.

Long Answer Type Questions:

(56) (a) Define the term latent heat of fusion of a solid. How much is the latent heat of fusion of ice?

(b) Draw a leveled diagram of the experimental set-up to study the latent heat of fusion of ice.

Ans. (a) The latent heat of fusion of a solid is the quantity of heat in joules required to convert 1 kilogram of the solid to liquid without any change in temperature.

The latent heat of fusion of ice – 3.34 x 105 joules per kilogram.

(57) (a) Define the term latent heat of vaporization of a liquid. What is the value of the latent heat of vaporization of water?

(b) Draw a leveled diagram of the experimental set up to study the latent heat of vaporization of water.

Ans. (a) The heat which is going into boiling liquid but not increasing its temperature is the energy required to change the state of liquid to gas. This is known as the latent heat of vaporization of liquid.

Latent heat of vaporization of water is 22.5 x 105 joules per kilogram.

(58) (a) What is sublimation? Name two substance which undergo sublimation.

(b) Draw a leveled diagram of the experimental sat up to demonstrate the sublimation of ammonium chloride.

Ans. (a) The changing of solid directly into vapours on heating and of vapours into solid on cooling is called sublimation.

Two substance which undergo sublimation are iodine, camphor.

(59) (a) What are the two ways in which the physical states of matter can be changed?

(b) Draw the states of matter triangle to show the interconversion of states of matter.

(c) How can the evaporation of a liquid be made faster?

Ans. (a)  Matter can change from one state to another if heated or cooled. If ice (a solid) is heated it changes to water (a liquid). This change is called MELTING. If water is heated, it changes to steam (a gas).

(c) Evaporation of a liquid be made faster By increasing or raising the temperature liquid can be evaporated faster.

(60) (a) What is evaporation? State the various factors which affect evaporation.

(b) Why does evaporation cool a liquid?

Ans. The process of a liquid changing into vapour (or gas) even below its boiling point is called evaporation.

The various factors which affect evaporation are:

(i) Temperature

(ii) Surface area

(iii) Humidity

(iv) Wind speed.

(b) Whenever a liquid evaporates, it must be supplied the latent heat of vaporization. The cool caused by evaporation is based on the fact that: when a liquid evaporates its takes the latin heat of vaporization from anything which it touches. By losing heat this anything gets cooled. For example: During summer day water is kept in an earthen pot to keep it cool. This is because the earthen pot has a large number of extremely small pores in its walls. Some of the water continuously keeps deeping through these pores to the outside of the pot. This water evaporates continuously and takes the latented heat required for vaporisation from earthen pot and the remaining water. In this way, the remaining water loses heat and gets cooled.


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