CBSE - Matter in Our Surroundings

Chair, air, almonds and cold drink

Solids diffuse at a very slow rate. But, if the temperature of the solid is increased, then the rate of diffusion of the solid particles into air increases. This is due to an increase in the kinetic energy of solid particles. Hence, the smell of hot sizzling food reaches us even at a distance, but to get the smell from cold food we have to go close.

This observation shows that the particles of matter have intermolecular spaces. The intermolecular spaces in liquids is fair enough to let the diver pass through it. 

The characteristics of particles of matter are:
→ Particles of matter have spaces between them.
→ Particles of matter are continuously moving.
→ Particles of matter attract each other.

air, Exhaust from chimneys, cotton, water, honey, chalk, and iron.

Property	Solid state	Liquid state	Gaseous state
	Definite shape and volume.	No definite shape. Liquids attain the shape of the vessel in which they are kept.	Gases have neither a definite shape nor a definite volume.
2.	Incompressible	Slightly Compressible	Highly compressible
3.	Cannot flow	Can flow	Can flow
4.	Particles don't move freely	Particles move freely but are confined within boundary.	Particles move freely.
5.	Force of attraction between particles are maximum.	Force of attraction between particles is less than solid but more than that in gas	Force of attraction between particles is least.

(b)
→ Rigidity: It is the property of matter to resist the change of its shape.→ Compressibility: It is the property of matter in which its volume is decreased by applying force.
→ Fludity: It is the ability of matter to flow.
→ Filling a gas container: On filling a gas takes the shape of the container.
→ Shape: Having definite boundaries.
→ Kinetic Energy: It is the energy possessed by the particles of matter due to its motion.
→ Density: It is the ratio of mass with per unit volume.

The force of attraction between particles of gas is negligible. Because of this, particles of gas move in all directions. Thus, a gas fills the vessel completely in which it is kept.

Particles of gas move randomly in all directions at high speed. As a result, the particles hit each other and also hit the walls of the container with a force. Therefore, gas exerts pressure on the walls of the container.

A wooden table has fixed shape and fixed volume, which are the main characteristics of solid. Thus a wooden table should be called a solid.

Particles of air have large spaces between them. On the other hand, wood has little space between its particles. Also, it is rigid. For this reason, we can easily move our hands in air, but to do the same through a solid block of wood, we need a karate expert.

Ice which is a solid has vacant spaces between water molecules thus making ice lighter than water. Thus ice floats on water.

Convert the following temperature to Celsius scale:

(a) 300 K

► 300 K = (300 - 273)°C
= 27°C

(b) 573 K

► 573 K = (573 - 273)°C
= 300°C

(a) 250°C

-> Gaseous State (As Boiling temperature of water is 100° C).

(b) 100°C

-> Since water boils at this temperature thus it can exist in both liquid and gaseous form. At this temperature, after getting the heat equal to the latent heat of vaporization, water starts changing from liquid state to gaseous state.

During the change of state of any substance, the heat supplied or released is utilised in phase change. Such heat is called latent heat. So, the temperature of any substance remains constant during the change of state.

The gases can be converted into liquids by bringing its particles closer so atmospheric gases can be liquefied either by decreasing temperature or by increasing pressure.

A desert cooler increases the humidity of the surrounding air. The water particles in the air take the heat from the surrounding objects and evaporates. In hot and dry days the moisture level is very low in atmosphere which increases the rate of evaporation. Because of faster evaporation, cooler works well. That’s why desert cooler cool better on a hot dry day.

There are some pores in an earthen pot through which the liquid inside the pot evaporates. This evaporation makes the water inside the pot cool. In this way, water kept in an earthen pot becomes cool during summers.

Acetone, petrol, and perfume evaporate at low temperatures. When some acetone, petrol, or perfume is dropped on the palm, it takes heat from the palm and evaporates, thereby making the palm cooler.

A liquid has a larger surface area in a saucer than in a cup. Thus, it evaporates faster and cools faster in a saucer than in a cup. Thus, we are able to sip hot tea or milk faster from a saucer than a cup.

We should wear cotton clothes in summers as cotton is a good sweat absorber. Sweat is absorbed by the cotton and is exposed to the atmosphere making evaporation faster. During this evaporation, particles on the surface of the liquid gain energy from our body surface, making the body cool.

(a) 300 K
-> 300 K = (300 - 273) °C
= 27 °C

(b) 573 K
-> 573 K = (573 - 273) °C
= 300 °C

(a) 25°C
-> 25 °C = (25 + 273) K
= 298 K

(b) 373°C
->  373 °C = (373 + 273) K
= 646 K

Naphthalene balls disappear with time without leaving any solid because they undegoes sublimation easily i.e., the change of state of naphthalene from solid to gas takes place easily.

Perfumes has high degree of vaporization and its vapour diffuse into air easily. Therefore, we can get the smell of perfume sitting several metres away.

Oxygen, Water, Sugar.

(a) 25°C
-> Liquid State

(b) 0°C
-> Solid State, can also be in liquid state(conditions required).

(c) 100°C
-> Gaseous State, can also be in liquid state(conditions required).

Water at room temperature is a liquid because it has fluidity also it has no shape but has a fixed volume that is, it occupies the shape of the container in which it is kept.

An iron almirah is a solid at room temperature it has rigid and fixed shape.

Ice at 273 K has less energy than water (although both are at the same temperature). Water possesses the additional latent heat of fusion. Hence, at 273 K, ice is more effective in cooling than water.

Steam has more energy than boiling water. It possesses the additional latent heat of vaporization. Therefore, burns produced by steam are more severe than those produced by boiling water.

ANSWER

1. Which one of the following sets of phenomena would increase on raising
the temperature?
(a) Diffusion, evaporation, compression of gases
(b) Evaporation, compression of gases, solubility
(c) Evaporation, diffusion, expansion of gases
(d) Evaporation, solubility, diffusion, compression of gases
Ans. (c) Evaporation, diffusion, expansion of gases
Explanation: Evaporation happens because of conversation of liquid into gas and this happens because of absorption of temperature by the liquid. Hence, rise in temperature increase the rate of evaporation. Rise in temperature increase the kinetic energy of particles and gases expand on rise in temperature. Increased kinetic energy of particles
also increases diffusion.

2. Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identify the correct set of
conditions
(a) Low temperature, low pressure
(b) High temperature, low pressure
(c) Low temperature, high pressure
(d) High temperature, high pressure
Ans. (c) Low temperature, high pressure
Explanation: Low temperature reduces the kinetic energy of particles. High pressure reduces intermolecular space. Both these conditions help in turning a gas into liquid. 

3. The property to flow is unique to fluids. Which one of the following statements is  correct?
(a) Only gases behave like fluids
(b) Gases and solids behave like fluids
(c) Gases and liquids behave like fluids
(d) Only liquids are fluids
Ans. (c) Gases and liquids behave like fluids
Explanation: In gases and liquids, space between molecules is enough which facilitates the flow of these matters.

4. During summer, water kept in an earthen pot becomes cool because of the phenomenon of
(a) diffusion
(b) transpiration
(c) osmosis
(d) evaporation
Ans. (d) evaporation
Explanation: Evaporation reduces the temperature of surroundings. Due to this, water in earthen pot cools down.

5. A few substances are arranged in the increasing order of ‘forces of attraction’ between their particles. Which one of the following represents a correct arrangement?
(a) Water, air, wind
(b) Air, sugar, oil
(c) Oxygen, water, sugar
(d) Salt, juice, air
Ans. (c) Oxygen, water, sugar
Explanation: Forces of attraction between particles is the least in gases and is maximum in solids.

6. On converting 25°C, 38°C and 66°C to kelvin scale, the correct sequence of
temperature will be
(a) 298 K, 311 K and 339 K
(b) 298 K, 300 K and 338 K
(c) 273 K, 278 K and 543 K
(d) 298 K, 310 K and 338 K
Ans. (a) 298 K, 311 K and 339 K
Explanation: 25oC + 273 = 298 K, 38oC + 273 = 311 K, 66oC + 273 = 339K.

7. Choose the correct statement of the following
(a) conversion of solid into vapours without passing through the liquid state is called vapourisation. 
(b) conversion of vapours into solid without passing through the liquid state is called sublimation.
(c) conversion of vapours into solid without passing through the liquid state is called freezing.
(d) conversion of solid into liquid is called sublimation.
Ans. (b) conversion of vapours into solid without passing through the liquid state is called sublimation.

8. The boiling points of diethyl ether, acetone and n-butyl alcohol are 35°C, 56°C and 118°C respectively. Which one of the following correctly represents their boiling points in kelvin scale?
(a) 306 K, 329 K, 391 K
(b) 308 K, 329 K, 392 K
(c) 308 K, 329 K, 391 K
(d) 329 K, 392 K, 308 K
Ans. (c) 308 K, 329 K, 391 K
Explanation: Add 273 to each Celsius scale to convert them to Kelvin scale. 

9. Which condition out of the following will increase the evaporation of water?
(a) Increase in temperature of water
(b) Decrease in temperature of water
(c) Less exposed surface area of water
(d) Adding common salt to water
Ans. (a) Increase in temperature of water
Explanation: The rest of the options reduce the rate of evaporation of water.

10. In which of the following conditions, the distance between the molecules of hydrogen gas would increase?
(i) Increasing pressure on hydrogen contained in a closed container
(ii) Some hydrogen gas leaking out of the container
(iii) Increasing the volume of the container of hydrogen gas
(iv) Adding more hydrogen gas to the container without increasing the volume of the container
(a) (i) and (iii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)
Ans. (c) (ii) and (iii)
Explanation: Increase pressure to adding more hydrogen gas to the container without increasing the volume of container will reduce the intermolecular distance. 
 

The boiling point of pure water is 100^o C at 1 atm. Consequently, pure water freezes at 0^o C. So, the sample of water which boils at 102^o C at normal temperature and pressure is not pure water. It will freeze below 0^o C.

Ans. Since ice and water are in equilibrium, the temperature would be zero. When we heat the mixture, energy supplied is utilized in melting the ice and the temperature does not change till all the ice melts because of latent heat of fusion. On further heating, the temperature of the water would increase. Therefore, the correct option is (d).

(a) Evaporation of a liquid at room temperature leads to a __________ effect.
(b) At room temperature, the forces of attraction between the particles of solid substances are __________ than those which exist in the gaseous state.
(c) The arrangement of particles is less ordered in the __________ state. However, there is no order in the __________ state.
(d) __________ is the change of gaseous state directly to solid state without going through the __________ state.
(e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called __________. 
Ans. (a) cooling
(b) stronger
(c) liquid, gaseous
(d) sublimation, liquid
(e) evaporation 

Ans. (a) � (iii) (b) � (iv) (c) � (v) (d) � (ii) (e) � (i)

Ans. (a) � (iv) (b) � (iii) (c) � (v) (d) � (ii) (e) � (i)

Yes, this is true. In both the phenomena, there is movement of particles from region of higher concentration to that of lower concentration. However, in the case of osmosis the movement of solvent is through a semi permeable membrane which is permeable only to water molecules.

(a) Swelling up of a raisin on keeping in water.

Ans. Osmosis

(b) Spreading of virus on sneezing.

Ans. Diffusion

(c) Earthworm dying on coming in contact with common salt.

Ans. Osmosis (d) Shrinking of grapes kept in thick sugar syrup.

Ans. Osmosis

(e) Preserving pickles in salt.

Ans. Osmosis

(f) Spreading of smell of cake being baked throughout the house.

Ans. Diffusion

(g) Aquatic animals using oxygen dissolved in water during respiration. Ans. Diffusion

In case of ice the water, molecules have low energy while in the case of steam the water molecules have high energy. The high energy of water molecules in steam is transformed as heat and may cause burns. On the other hand, in case of ice, the water molecules take energy from the body and thus give a cooling effect.

The temperature of both boiling water and steam is 100°C, but steam has more energy because of latent heat of vapourisation.

Ans. (a) The water will cool initially till it reaches 0�C, the freezing point. At this stage the temperature will remain constant till all the water will freeze. After this temperature, would fall again.

(c) The rate of evaporation increases with an increase of surface area because evaporation is a surface phenomenon. Also, with the increase in air speed, the particles of water vapour will move away with the air, which will increase the rate of evaporation.

Sublimation

The amount of heat required to convert 1 kg of solid into liquid at one atmosphere pressure at its melting point is known as its latent heat of fusion.

Ans. Naphthalene is insoluble in water but soluble in ether an organic solvent. It is volatile at room temperature. Ammonium chloride is soluble in water and volatile at higher temperature. It decomposes on heating to dryness.

Cotton being a better absorber of water than nylon helps in absorption of sweat followed by evaporation which leads to cooling. So Priyanshi is more comfortable, whereas Ali is not so comfortable.

Conditions that can increase the rate of evaporation of water are
(a) an increase of surface area by spreading the shirt
(b) an increase in temperature by putting the shirt under the sun
(c) increase the wind speed by spreading it under the fan.

Evaporation produces cooling as the particles at the surface of the liquid gain energy from the surroundings and change into vapour thereby producing a cooling effect.

Air around us cannot hold more than a definite amount of water vapour at a given temperature which is known as humidity. So, if the air is already rich in water vapour, it will not take up more water therefore, rate of evaporation of water will decrease.

A sponge has minute holes in which air is trapped. Also, the material is not rigid. When we press it, the air is expelled out and we are able to compress it.

The temperature of a substance remains constant at its melting and boiling points untill all the substance melts or boils because, the heat supplied is continuously used up in changing the state of the substance by overcoming the forces of attraction between the particles. This heat energy absorbed without showing any rise in temperature is given the name latent heat of fusion/latent heat of vapourisation