JKBOSE 9th Class Science Solutions Chapter 7 Matter In Our Surroundings 

◆The rate of evaporation depends upon the surface area, temperature, humidity and wind speed.

◆ Evaporation causes cooling.

◆ Boiling is a fast process whereas evaporation is a slow process.

◆ Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.

◆ Latent heat of vaporisation is the amount of heat energy required to change 1 kg of a liquid to gas at atmospheric pressure and at its boiling point.

◆ Sublimation. It is the process due to which a solid directly changes into gaseous state on heating and a gaseous state directly changes into solid state on cooling without changing into liquid state.

◆ Vapour. It is a substance which exists in the gaseous state at a temperature lower than the boiling point of its liquid state.

⇒ Temperature on Kelvin scale = 273 + Temperature on centigrade scale.

TK = 273 + tºC

⇒ Water freezes at 0ºC or 273 K.

⇒ Water boils at 100ºC or 373 K.

⇒ Unites of Latent heat of fusion are k J / kg or kcal / kg.

⇒ Unites of Latent heat of vaporisation are kJ / kg  or kcal / kg.

⇒ F – 32 / 9 = C / 5 , F = Temperature on Fahrenhiet  scale.

                              C = Temperature on Centigrade scale.

Ans.— Chair, air, almonds, cold drink, smell of perfume.

Ans.— The smell of hot sizzling food reaches us several metres away, but to get the smell from cold food we have to go close. This is because the rate of diffusion of a gas increases with the increase in temperature. In hot food, the rate of diffusion is large but in cold food, the rate of diffusion is slow.

Ans.— The diver is able to cut through water in a swimming pool because in water the attractive forces between the molecules are small.

Ans.— The characteristics of the particles of matter are :

1. The particles of matter have vacant spaces between them.

2. The particles of matter are always in motion.

3. There are attractive forces between the particles of matter.

Ans.— The increasing order of density is

Exhaust from chimnies < air < cotton < chalk < honey < iron.

Characteristics	Solid	Liquid	Gas
Vacant space	Very small	Small	very large
Attractive forces between particles	Very large	Small	Negligible
Compressibility	Negligible	Low	High
Rigidity	High	Low	Now rigid
Density	High	Low	Very Low
Energy	Small	Large as compared to solid	Very high

(b) Rigidity. It is the property by virtue of which a substance can retain its shape when a force is applied to it. Solids possess the property of rigidity.

Compressibility. The property by virtue of which the volume of a substance can be decreased by applying force or pressure on it. Gases have high compressibility because of large vacant spaces between the molecules of a gas.

Fluidity. It is the property by virtue of which the molecules of one substance can flow from one point to another. Liquids and gases possess fluidity.

Filling a gas container. A gas fills the container because there are negligible attractive forces between the molecules of a gas and the molecules of a gas move with very high velocities in all possible directions.

Shape. It is the definite geometrical arrangement of constituent particles of a substance. Solids have definite shapes.

Kinetic energy. It is the energy possessed by a particle due to its motion.

Density. Density of a substance is the mass per unit volume. Its units are g/cc or kg/m³.

Ans.— (a) This is because in a gas the attractive forces between the particles are negligible and molecules of a gas move with very high speeds in all possible directions.

(b) This is due to the hits or bombardments of the molecules of a gas against the walls of a container.

(c) This is because it has a definite mass, volume and shape.

(d) This is because in air, the attractive forces between the particles are negligible but in a solid block of wood, there are large attractive forces between the constituent particles.

Ans.— Ice floats over water because ice has lower density than liquid water. This is because in ice for a given mass volume is more as compared to in liquid water.

Ans.— (a) 300 K = 300 – 273 = 27°C.

(b) 573 K = 573 –  273 = 300°C.

Ans.— (a) Gas (b) Gas

Ans.— This is because the heat supplied is used to overcome the attractive forces between the particles i.e., there is change in potential energy.

Ans.— The atmospheric gases can be liquefied by cooling under pressure.

Ans.— This is because on a hot dry day, due to increase in temperature and lesser humidity the evaporation of water will be faster.

Ans.— This is because the water comes out from the pores of earthen pot (matka) and it evaporates. Due to evaporation it causes cooling.

Ans.— This is because the particles of acetone or petrol or perfume gain energy from our palm and surroundings and evaporate causing cooling.

Ans.— Because a saucer provide more surface area than cup for evaporation of liquid into vapour and it causes more cooling effect.

Ans.— White cotton clothes.

Ans.— (a) 293 K = 293 – 273 = 20°C

(b) 470 K= 470 – 273 = 197°C

Ans.— (a) 25°C = 25 + 273 = 298 K

(b) 373°C = 373 + 273 = 646 K

Ans.—  (a) This is because naphthalene sublimes i.e. it directly changes into vapour without melting.

(b) This is because the molecules of perfume are moving with very high velocities (i.e. diffusion) in all the directions.

Ans.— The increasing order of intermolecular forces of attraction is Oxygen < Water < Sugar.

Ans.—  (a) At 25° C, water is liquid.

(b) At 0° C, water is solid (Ice).

(c) At 100° C, water is gas (Steam).

Ans.— (a) At room temperature water is liquid because the attractive forces between the molecules of water are small and can move from one point to another.

(b) An iron almirah is solid because the molecules are held together by strong intermolecular attractive forces and the molecules or particles are very close to each other.

Ans.—  Ice at 273 K is more effective in cooling than water at 273 K, this is because in ice, the molecules have lower energy as compared to the particles in the liquid water at the same temperature (273 K) and require latent heat of fusion for melting.

Ans.— Steam produces severe burns as compared to boiling water. This is because in steam the molecules have higher kinetic energies than in boiling water.

Ans.— Solid. In solids the constituent particles are closely packed and there are attractive forces between them. Therefore, the particles have low kinetic energies and can’t move from one position to another but they have only vibratory motion. Hence solids have definite shapes and definite volumes, e.g. wood, rock, copper, iron, cement, stone etc.

Liquid. In liquids the molecules have higher kinetic energies, distances between the molecules are more and attractive forces between the molecules are small. Therefore, the molecules of a liquid can move from one position to the another within the liquid. Hence the liquid can take the shape of the container. But the volume of the liquid remains fixed because the molecules can’t leave the liquid, e.g. alcohol, milk, benzene, kerosene oil, petrol etc.

Gas. In the gases, the molecules have high kinetic energies, there are large vacant spaces between the molecules and there are negligible attractive forces between the molecules. Therefore, in the gases molecules can move randomly and occupy the whole space available to them. Hence, they don’t have definite volumes and shapes, e.g. hydrogen, oxygen, nitrogen, sulphur dioxide, carbon dioxide etc.

Ans.— (a) Sublimation. It is the process in which a solid directly changes into vapour on heating and on cooling the gas directly changes into solid.

Dry ice and iodine sublime.

(b) Solid. It is that state of matter which has definite mass, volume and shape. e.g. sugar, rubber, table, stone etc.

The solids don’t diffuse because in the solid state the vacant spaces between the molecules are very small and molecules of a solid can’t move from one position to another.

(c) Liquid. A liquid is that state of matter which has definite mass and volume but has no definite shape. e.g. milk, petrol, kerosene oil, water etc.

Liquids flow because the attractive forces between the molecules of a liquid small and the molecules can freely move within the liquid.

(d) Freezing point. It is the temperature at which a liquid changes into a solid state by giving out heat energy. For examples freezing point of water is 0°C.

(e) Gas. It is defined as that state of matter which has definite mass only but has neither definite shape nor definite volume. For example, carbon dioxide, oxygen, hydrogen, ammonia etc.

The gases are compressible and show diffusion because there are large vacant space between the molecules of a gas and molecules of a gas are always in motion.

Ans.—  1. Three 2. large 3. cooling 4. decreasing, increasing 5. one.

Ans.— (a) True (b) True (c) False (d) True (e) True.

Ans.— The process of change of matter from one state to another is called interconversion of states of matter. The states of matter can be changed by changing temperature and pressure.

1. By changing temperature. By increasing temperature, the solid can be changed into liquid and liquid can be changed into gas. This is because on increasing temperature, the kinetic energies of the molecules increase and they can move freely. The reverse changes occur on cooling.

For example, ice changes into liquid water at 0°C and water changes into steam at 100°C (under normal pressure).

2. By changing pressure. When the pressure is lowered the liquid starts boiling at a lower temperature and changes into gaseous state. Similarly, by applying high pressure, a gas can be liquefied.

For example, carbon dioxide can be liquefied by applying a pressure of 70 atmosphere under normal temperature.

Ans.— This is because these are massless and do not occupy space.

Ans.— These are :

1. Plasma. It is produced in stars at very high temperature.

2. Bose-Einstein condensate. It is formed by cooling a gas of extremely low density to super low temperature.

Ans.— Examples of solids. Iron, copper, silver, glass and wood.

Examples of liquids. Water, milk, mercury, kerosene oil and petrol.

Examples of gases. Hydrogen, oxygen, carbon dioxide, nitrogen, helium.

Ans.— A gas is a substance which exists in the gaseous state at a temperature equal to or more than the boiling point of its liquid state. e.g. oxygen, hydrogen, nitrogen etc.

A vapour is a substance which exists in the gaseous state such that its temperature is lower than that of boiling point of its liquid state e.g. water vapour, iodine vapour etc.

Ans.— Rubber band is a solid because it changes its shape under force and return to its original state when the applied force is removed.

Ans.—The liquid will change into solid. This is carried out by decreasing the temperature or cooling the liquid.

Ans.— This is because water vapour present in air, on coming in contact with glass containing ice-cold water lose energy and get converted into liquid state which appear as water droplets.

Ans.— This is because in summer, we perspire more and cotton being a good absorber of water, absorbs the sweat and exposes it to the atmosphere for easy evaporation and evaporation causes cooling by absorbing heat from the surroundings or body surface.

Ans.— (a) When ammonium chloride is heated in a hard glass test tube, dense white fumes of ammonium chloride fill the tube and deposit to give a white powder near the mouth of the tube (cooler parts).

(b) When carbon dioxide is compressed to 70 atmospheric pressure, it changes into solid state.

Ans.— Th is because sponge has minute holes in which there is entraped air. When it is pressed, the air is expelled out.

Ans.— The molecules in a gas are far apart and are in a state of rapid random motion in all possible directions with very high speeds. They move throughout the container in which they are put. Thus, a gas fills the container completely.

Ans.— These are :

 1. Water is converted into steam by heating. Steam is used to run turbines and to generate electricity.

2. Metals are melted by heating and these molten metals can be converted into alloys and cast into machinery parts.

3. Water can be changed into steam as well as ice. Therefore, in nature, ice (or snow), liquid water and water vapour are available.

Boiling	Evaporation
It takes place at a fixed temperature called boiling point of the liquid.	It takes place at all temperatures.
It is a fast process.	It is a slow process

Ans.— There are :

1. Exposed surface area

2. Temperature

3. Humidity in the air

4. Wind speed.

Ans.— Take a 100 ml syringe and close its nozzle by inserting it in a rubber cork or stopper. Remove the piston from the syringe so that whole of syringe is filled up with air. Apply a little vaseline to the piston and insert the piston. Compress piston and it moves downwards easily. Hence air is compressed to m a very small volume.

Now fill the syringe with water and repeat the above experiment. The piston moves hardly downwards, indicating that there is a negligible compression in volume.

The above experiment indicates that gases are highly compressible as compared to liquids.

Ans.— The gases from the atmosphere diffuse and dissolve in water. There gases mainly contain carbon dioxide and oxygen. These are taken up for their by the aquatic plants and animals survival.

Ans.— When some crystals of iodine are heated slowly in a test tube, the shiny grey iodine changes directly into vapour without melting. The vapour deposit as grey particles called sublimate on the upper cooler parts of the tube.

Ans.—  Air < Water < Honey < Iron (Increasing order of Density)

(i) Size of naphthalene balls decreases

(ii) Wax melts in the sun

(iii) Drying of wet clothes

(iv) Formation of clouds.

Ans.—  (i) Sublimation

(ii) Fusion

(iii) Evaporation

(iv) Condensation.

Ans.— (i) liquid, solid. (ii) temperature, temperature. (iii) gaseous, gas, solid, sublimation. (iv) minimum, maximum.

Ans.— Iodine, ammonium chloride, camphor, naphthalene.

Ans.— This is because in the solids, the particles are closely packed and the vacant spaces between them are negligible.

Ans.— (a) Carbon dioxide gas.

(b) Sodium chloride.

Ans.— The three states of matter occupy space and have mass.

Ans.— 1. Fluidity 2. Compressibility.

Ans.— This is due to the bombardment of the molecules of a gas against the walls of the container.

Ans.— This is because there are some vacant spaces between the particles and less attractive forces between the particles.

Ans.— This is because in gases the vacant spaces between the particles are very large as compared to that in liquids.

Ans.— Sound is not considered to be matter because it has no mass and does not occupy space.

Light has dual character. Sometime it behaves as matter and sometime behaves as wave.

Ans.— This is because during the process of melting and boiling the heat energy supplied is absorbed by the molecules to increase potential energy and to decrease the attractive forces between the molecules.

(A) Definite shape, compressible, fixed volume.

(B) Definite shape, highly compressible, fixed volume.

(C) No definite shape, highly compressible, closely packed.

(D) Definite shape, incompressible, closely packed.

Ans.— (D) Definite shape, incompressible, closely packed.

(A) Solid

(B) Liquid

(C) Gas

(D) May be solid or liquid.

Ans.— (B) Liquid

(A) Solid

(B) Liquid

(C) Gas

(D) None.

Ans.— (C) Gas

(A) Buring of saw dust

(B) Burning of log of wood

(C) Burning of Coal pieces

(D) All are fast processes.

Ans.—(A) Buring of saw dust

(A) Air

(B) Smell

(C) Chair

(D) Cold drink.

Ans.— (A) Air

(A) Solids

(B) Liquids

(C) Gases

(D) None.

Ans.— (A) Solids

(A) Solids

(B) Liquids

(C) Gases

(D) All.

Ans.— (A) Solids

(A) Solid

(A) Solid

(C) Gas

(D) All are equally compressible.

Ans.— (A) Solid

(B) 27°C

(C) 300°C

(D) -27°C.

Ans.— (B) 27°C