Ch-1: Matter in Our Surroundings

Chapter 1 – Matter in Our Surroundings 

Exercise-1.1-1.2 Page: 3

1. Which of the following are matter?

Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.

Solution:

The following substances are matter:

Chair

Air

Almonds

Lemon water.

2. 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.

Solution:

Particles in the air, if fueled with higher temperatures, acquire high kinetic energy which aids them

to move fast over a stretch. Hence the smell of hot sizzling food reaches a person even at a distance

of several meters.

3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Solution:

The diver is able to easily cut through the water in the swimming pool because of the weak forces of

attraction between water molecules. It is this property of water that attributes to easy diving.

4. What are the characteristics of the particles of matter?

Solution:

The characteristics of particles of matter are:

(a) Presence of intermolecular spaces between particles

(b) Particles are in constant motion

(c) They attract each other

Exercise-1.3 Page: 6

1. The mass per unit volume of a substance is called density. (density=mass/volume). Arrange the following in the order of increasing density – air, exhaust from the chimneys, honey, water, chalk, cotton and iron.

Solution:

The following substances are arranged in the increasing density:

Air

Exhaust from chimney

Cotton

Water

Honey

Chalk

Iron

2. Answer the following.

a) Tabulate the differences in the characteristics of matter.

b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container,

shape, kinetic energy and density.

Solution:

(a) The difference in the characteristics of the three states of matter.

Characteristics	Solid	Liquid	Gas
Shape	Fixed shape	No Fixed shape	No Fixed shape
Volume	Fixed volume	Fixed volume	No Fixed volume
Intermolecular force	Maximum	Less than solids	Very less
Intermolecular space	Very less	More than solids	maximum
Rigidity/Fluidity	Rigid/cannot flow	Can flow/not rigid	Can flow/not rigid
Compressibility	negligible	compressible	Highly compressible

(b) (i) Rigidity: It is the propensity of a substance to continue to remain in its shape when treated

with an external force.

(ii) Compressibility: It is the attribute of the particles to contract its intermolecular space when

exposed to an external force thereby escalating its density.

(iii) Fluidity: It is the ability of a substance to flow or move about freely.

(iv) Filling the gas container: The particles in a container take its shape as they randomly vibrate in

all possible directions.

(v) Shape: It is the definite structure of an object within an external boundary

(vi) Kinetic energy: Motion allows particles to possess energy which is referred to as kinetic

energy. The increasing order of kinetic energy possessed by various states of matter are:

Solids < Liquids < Gases

Mathematically, it can be expressed as K.E =12mv2, where ‘m’ is the mass and ‘v’ is the velocity

of the particle.

(vii) Density: It is the mass of a unit volume of a substance. It is expressed as:

d = M/V, where ‘d’ is the density, ‘M’ is the mass and ‘V’ is the volume of the substance

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.

Solution:

a) Kinetic energy possessed by gas particles is very high which allows them to randomly move

across all directions when contained, hence the particles fills the gas vessel entirely.

b) Gas molecules possess high kinetic energy, due to which they are under constant motion inside

the container in random directions which causes them to hit the walls of the container and hence create vibrations. These collisions with the walls of the container generate pressure.

c) A wooden table should be called a solid as it possesses all the properties of a solid such as:

1. 1. • Definite size and shape
      • Intermolecular attraction between closely packed particles.
      • It is rigid and cannot be compressed

d) Molecules in gases are loosely packed as compared to solid molecules which are densely packed.

Hence we are easily able to break the force of attraction when we move our hand through air but find it difficult to break through a solid (because of greater forces of attraction between molecules) which a karate expert is able to smash with the application of a lot of force.

1. 1. 4. Liquids generally have a lower density than solids. But you must have observed that ice floats on water. Find out why.

Solution:

Density of ice is less than the density of water. The low density of ice can be attributed to the small

pores it has which allows it to trap air hence ice floats on water.

Exercise-1.4 Page: 9

1. 1. 1. Convert the following temperature to Celsius scale:

a. 300K          b. 573K

Solution:

a.  0°C=273K

300K= (300-273)°C = 27°C

b. 573K= (573-273)°C = 300°C

1. 1. 2. What is the physical state of water at:

a. 250°C         b. 100°C ?

Solution:

(a) At 250°C – Gaseous state since it is beyond its boiling point.

(b) At 100°C – It is at the transition state as the water is at its boiling point. Hence it would be

present in both liquid and gaseous state.

1. 1. 3. For any substance, why does the temperature remain constant during the change of state?

Solution:

It is due to the latent heat as the heat supplied to increase the temperature of the substance is used up to transform the state of matter of the substance hence the temperature stays constant.

1. 1. 4. Suggest a method to liquefy atmospheric gases.

Solution:

It can be achieved by either increasing the pressure or decreasing the temperature which ultimately leads to the reduction of spaces between molecules.

Exercise-1.5 Page: 10

1. 1. 1. Why does a desert cooler cool better on a hot dry day?

Solution:

It is because the temperature is high and it is less humid on a hot dry day which enables better evaporation. High levels of this evaporation provide better cooling effects.

1. 1. 2. How does the water kept in an earthen pot (matka) become cool during summer?

Solution:

An earthen pot is porous in nature. These tiny pores facilitate penetration of water and hence their evaporation from the pot surface. The process of evaporation requires energy which is contributed by water in the pot as a result of which water turns cooler.

1. 1. 3. Why does our palm feel cold when we put on some acetone or petrol or perfume on it?

Solution:

Acetone, petrol, and perfume are volatile substances that get evaporated when they come in contact

with air. Evaporation is facilitated as it uses energy from palm hence leaving a cooling effect on our

palms.

1. 1. 4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

Solution:

A saucer has a larger surface area than a cup which promotes quicker evaporation hence the tea or milk in a saucer cools down faster.

1. 1. 5. What type of clothes should we wear in summer?

Solution:

In summer, it is preferred to wear light-colored cotton clothes because light color reflects heat and cotton materials have pores that absorb sweat, facilitating their evaporation hence causing a cooling effect in the skin.

Exercise Page: 12

1. 1. 1. Convert the following temperature to Celsius scale.

(a) 293K                (b) 470K

Solution:

0°C=273K

(a) 293K= (293 – 273)°C = 20°C

(b)  470K= (470 – 273)°C = 197°C

1. 1. 2. Convert the following temperatures to the Kelvin scale.

(a) 25°C                (b) 373°C

Solution:

0°C = 273K

(a) 25°C = (25+273)K = 298K

(b) 373°C = (373+273)K = 646K

1. 1. 3. Give reason for the following observations:

(a) Naphthalene balls disappear with time without leaving any solid.

(b) We can get the smell of perfume while sitting several metres away.

Solution:

1. 1. 4. At room temperature, naphthalene balls undergo sublimation wherein they directly get converted

from a solid to a gaseous state without having to undergo the intermediate state, i.e., the liquid state.

1. 1. 1. Molecules of air move at a higher speed and have large intermolecular spaces. Perfumes comprise

of flavoured substances that are volatile which scatters quickly in air, becoming less concentrated over a distance. Hence we are able to smell perfume sitting several metres away.

1. 1. 5. Arrange the following in increasing order of forces of attraction between the particles – water, sugar, oxygen.

Solution:

Oxygen (gas) < water (liquid) < sugar (solid)

1. 1. 6. What is the physical state of water at –  

(a) 25°C (b) 0°C (c) 100°C?

Solution:

(a) At 25°C, the water will be in liquid form (normal room temperature)

(b) At 0°C, the water is at its freezing point, hence both solid and liquid phases are observed.

(c) At 100°C, the water is at its boiling point, hence both liquid and gaseous state of water (water

vapor) are observed.

1. 1. 7. Give two reasons to justify –

(a) Water at room temperature is a liquid.

(b) An iron almirah is a solid at room temperature.

Solution:

(a) Transition in the states of matter of water occurs at 0°C and 100°C. At room temperature, water

is in the liquid state, thereby exhibiting all the properties of a liquid such as

1. 1. • Water flows at this temperature
      • It has a fixed volume and it takes the shape of its container

(b) The melting and boiling points of iron are as high as 1538°C and 2862°C respectively. The room

temperature is about 20-25 °C. Hence iron almirah is a solid at room temperature.

1. 1. 8. Why is ice at 273K more effective in cooling than water at the same temperature?

Solution:

Water at this temperature(273K) is less effective than ice as ice can readily form water through absorption of ambient heat energy as opposed to water which does not exhibit this property as it already possesses additional latent heat of fusion so does not require extra heat. Hence ice cools rapidly compared to water at the same temperature.

1. 1. 9. What produces more severe burns, boiling water or steam?

Solution:

Steam produces severe burns. It is because it is an exothermic reaction that releases high amount of heat which it had consumed during vaporization.

1. 1. 10. Name A, B, C, D, E and F in the following diagram showing a change in its state.

Solution:

A: Melting (or) fusion (or) liquefaction

B: Evaporation (or) vaporization

C: Condensation

D: Solidification

E: Sublimation

F: Sublimation

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NOTES AND DEFINITIONS

States of Matter

• Matter can be classified as solid, liquid and gas on the basis of interparticle forces and the arrangement of particles.
• These three forms of matter are interconvertible by increasing or decreasing pressure and temperature.  For example, ice can be converted from solid to a liquid by increasing the temperature.

Property	Solid	Liquid	Gas
Shape and volume	Fixed shape and volume	No fixed shape but has volume	Neither definite shape nor volume
Energy	Lowest	Medium	Highest
Compressibility	Difficult	Nearly difficult	Easy
Arrangement of molecules	Regular and closely arranged	Random and little sparsely arranged	Random and more sparsely arranged
Fluidity	Cannot flow	Flows from higher to lower level	Flows in all directions
Movement	Negligible	Depends on interparticle attraction	Free, constant and random
Interparticle space	Very less	More	Large
Interparticle attraction	Maximum	Medium	Minimum
Density	Maximum	Medium	Minimum
Rate of diffusion	Negligible	It depends on interparticle attraction.	Maximum

Atomic view of the three states of matter

Solid

Liquid

Gas

Evaporation

The phenomenon by which molecules in liquid state undergo a spontaneous transition to the gaseous phase at any temperature below its boiling point is called evaporation.

• For example, the gradual drying of damp clothes is caused by the evaporation of water to water vapour.

Factors affecting evaporation

• Temperature: The rate of evaporation increases with an increase in temperature.
• Surface area: The rate of evaporation increases with an increase in surface area.
• Humidity: The rate of evaporation decreases with an increase in humidity.
• Wind speed: The rate of evaporation increases with an increase in wind speed.

Cooling due to evaporation

During evaporation, the particles of a liquid absorb energy from the surroundings to overcome the interparticle forces of attraction and undergo the phase change. The absorption of heat from the surrounding makes the surrounding cool.
For example, sweating cools down our body.

Physical Nature of Matter

• A physical property is that aspect of the matter that can be observed or measured without changing its nature or composition.
• It is independent of the amount of matter present.
• Physical properties include appearance, colour, odour, density, texture, melting point, boiling point, solubility, etc.

Characteristics of Particles of Matter

Matter

Matter is anything that has mass and occupies space.

• Everything that we can touch, see, hear, taste, and also smell is matter.
• It is made up of really tiny particles which cannot be seen through the eye.

The particles of which the matter is comprised of influence its state and properties (physical and chemical).

1. Particles of matter have spaces between them

• This characteristic is one of the concepts behind the solubility of a substance in other substances. For example, on dissolving sugar in water, there is no rise in water level because the particles of sugar get into the interparticle spaces between the water particles.

2. Particles of matter are always in motion

• Particles of the matter show continuous random movements due to the kinetic energy they possess.
• A rise in temperature increases the kinetic energy of the particles, making them move more vigorously.

3. Particles of matter attract each other
In every substance, there is an interparticle force of attraction acting between the particles. To break a substance we need to overcome this force. The strength of the force differs from one substance to another.

Diffusion

When the particles of matter intermix on their own with each other, the phenomenon is called diffusion. For example, spreading of ink in water.

• During diffusion, the particles are occupying the interparticle spaces.
• The rate of diffusion increases with increase in the temperature, due to increase in kinetic energy of the particles.

Can Matter Change Its State?

Effect of change of temperature on state of matter

On increasing temperature, the kinetic energy of the particles of the matter increases and they begin to vibrate with a higher energy. Therefore, the interparticle force of attraction between the particles reduces and particles get detached from their position and begin to move freely.

• As a result, the state of matter begins to change.
• Solids undergo a phase change to form liquids.
• Similarly, liquids also undergo a phase change to form gases.

Melting point

The melting point of a solid is defined as the temperature at which solid melts to become liquid at the atmospheric pressure.

• At melting point, these two phases, i.e., solid and liquid are in equilibrium, i.e., at this point both solid state and liquid state exist simultaneously.

Boiling point

The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure.

Latent heat of fusion

It is the amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point.

Latent heat of vaporisation

It is the amount of heat energy that is required to change 1 kg of a liquid into gas at atmospheric pressure at its boiling point.

Sublimation

The transition of a substance directly from its solid phase to gaseous phase without changing into the liquid phase (or vice versa) is called sublimation.

Effect of change in pressure on state of matter

By applying pressure, the interparticle spaces between particles of matter decreases. Thus, by applying pressure and reducing temperature we can convert a solid to liquid and a liquid to gas.

Flowchart for inter-conversion of the three states of matter

IMPORTANT EXTRA QUESTIONS

Question 1.

A rubber band can change its shape on stretching. Will you classify it as solid or not? Justify?

Answer

Rubber band changes shape under force and regains the shape when the force is removed. So, it is classified as a solid.

Question 2.

Sponge, though compressible, is a solid?

Answer

A sponge has minute holes in which air is trapped. When we press it, the air is expelled out and we are able to compress it. On releasing pressure, it again regains its shape. So, it is classified as a solid.

Question 3.

Gases completely fill the vessel in which they are kept. Give reasons.

Answer

In the gaseous state, particles move freely and have greater space between them. So they occupy the entire space available. Hence, gases completely fill the vessel in which they are kept.

Question 4.

Under what conditions gases can be liquefied? In which form LPG is filled in gas cylinder?

Answer

By applying pressure and reducing temperature, gases can be liquefied. The liquefied petroleum gas (LPG) is filled in gas cylinders in the compressed gas form.

Question 5.

Liquid generally have lower density as compared to solids, but ice floats on water. Find out, why.

Answer

Ice and water both are the same substance but ice has greater volume than that of the same amount of water.

As density is inversely proportional to the volume, ice is less denser than water.

Objects having density less than water float on the surface of water.

Question 6.

What is dry ice?

Answer

Solid 

$C{O}_2$

 is called dry ice, because solid 

$C{O}_2$

 gets converted directly into gaseous state without coming into liquid state on decreasing pressure to one atmosphere.

Question 7.

Explain why temperature remains constant during interconversion of states of matter?

Answer

Heat supplied to a substance is getting used during changing its state to overcome the force of attraction between the particles. The excess heat is absorbed by the particles in the form of latent heat.

Question 8.

Give reason to explain why it takes longer time to dry wet clothes in humid weather?

Answser

Rate of evaporation depends on humidity present in air. Humid air already has large amount of water vapours, so rate of evaporation is slow.

Question 9.

Why should we wear cotton clothes during summer?

Answer

We perspire more during summer. Cotton is a good absorber of water. It absorbs sweat and exposes it for easy evaporation. As a result body feels cool and comfortable. So, we should wear cotton clothes during summer.

Question 10.

Why does a desert cooler cool better on a hot dry day?

Answer

The humidity that is the amount of water vapours in air is less on a hot dry day. Lesser the humidity more is the rate of evaporation. Since the rate of evaporation is more on a hot dry day, a desert cooler cools better.

Question 11.

Why do people sprinkle water on the roof after a hot sunny day?

Answer

After a hot sunny day, people sprinkle water on the roof or open ground because the large latent heat of vaporisation of water helps to cool the surface. Water takes away the heat from the ground and gives cooling effect.

Question 12.

Write any three differences between evaporation and boiling?

Answer

Question 13.

Why does ice at 0°C appear colder than water at same temperature?

Answer

Particles in water at 0° C (273K) have more energy as compared to the particles in ice at the same temperature. It is due to the latent heat o fusion.

Question 14.

Why mixture does not have a fixed melting point or a fixed boiling point? Give two reasons?

Answer

It does not have fixed composition and it does not have uniform ordered arrangement of particles.

Question 15.

On suffering from fever which will lower down your body temperature, more ice or ice cold water?

Answer

Ice will lower down body temperature more because it will take latent heat of fusion from our body and fever will come down faster.

Question 16.

What is tincture of iodine?

Answer

A solution of iodine in alcohol is known as tincture of iodine. Solute is iodine and solvent is alcohol.

Question 17.A gas exerts pressure on the walls of container, why?

Answer

Gas molecules collide with each other as well as with the walls of container. Therefore, gas exerts pressure.

Question 18.

The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.

Answer

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.

Question 19.

Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.

Answer

Question20.

What is the physical state of water at:

(a) 250°C

(b) 100°C

Answer

Question 21.

Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Answer

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.

Question 22.

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.

Answer

Naphthalene balls disappear with time without leaving any solid because they undergo 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 metre away.

Question 23.

Give two reasons to justify-

(a)Water at room temperature is a liquid.

(b)An iron almirah is a solid at room temperature.

Answer

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.

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

Question 24.

A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 0⁰C). If you could measure the temperature of the content of the tumbler, which of the following graphs would correctly represent the change in its temperature as a function of time.

Answer

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).

Question 25.

i.Convert the following Kelvin temperature to degrees Celsius.

a. 173 K

b. 273 K

c. 400 K

ii.Convert the following Celsius temperature to Kelvin temperature.

a. -73 ° C

b. -23 ° C

c. 100 ° C

Answer

i. We know that ° Celsius = K - 273

a. ° C= K−273=173−273

$K-273=173-273$

     =-100 ° C

b. ° C= K−273=273−273

$K-273=273-273$

    = 0 ° C

c. ° C= K−273=400−273

$K-273=400-273$

    = 127° C

ii. We know that K = ° C + 273

a. K=° C + 273 = -73 + 273 = 200 K

b. K=° C + 273 = -23 + 273 = 250 K

c. K=° C + 273 = 100 + 273 = 373 K

Submitted by- Dhrubajyoti Barman

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