CHAPTER 1

MATTER IN OUR SURROUNDINGS Sushant Arora

(BCA, PGDCA, MCA)

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Matter in Our Surroundings

Matter can be anything that occupies space and has mass. E.g. chair, table etc.

PHYSICAL NATURE OF MATTER

• MATTER IS MADE UP OF PARTICLES

When we dissolve salt in water, the particles of salt get into the spaces between particles of water

and spreads throughout the water uniformly, hereby the water level rises.

• Particles of matter are very small and they cannot be seen with naked eyes.

If we take 2-3 potassium permanganate crystals and dissolve them in 100ml of water in a beaker,

solution becomes pink/purple. Then, if we transfer 10 ml of this solution to another beaker containing

clear water, its colour will also change to pink but it will be lighter as compared to the colour in the

initial beaker. If we keep on diluting the solution like this the colour shall become light but is still

visible.

By this we may conclude that each crystal of potassium permanganate contains millions of tiny

particles.

Characteristics of Particles of Matter

1. Particles of matter have space between them When we prepare sugar solution then, sugar gets completely dissolved in water because the sugar particles get into the spaces in between water molecules.

2. Particles of matter are continuously moving. If we lit up an incense stick at the corner of the room, we shall get the smell even if we are sitting at a distance which means that particles of matter are continuously moving.

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3. Particles of matter attract each other.

Particles of matter have force acting between them. This force is called as Inter-Particle force of attraction. This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another.

E.g. If we take an iron nail, a piece of chalk and a rubber band and try to break them by hammering, cutting and stretching. We shall observe that it is very difficult to break an iron nail because the inter-particle force of attraction is higher in it than chalk or rubber band. Hence, we shall require a greater force to break the inter-particle force of attraction in Iron nail.

Q. How does increase in temperature effects the movement of particles of matter?

Particles of matter are continuously moving, that is, they possess kinetic energy. As the temperature

rises, particles move faster. So, with increase in temperature the kinetic energy of the particles also

increases and hence, the particles move faster.

Q. What is diffusion?

The intermixing of particles of two different types of matter on their own is called as diffusion.

E.g. If we add sugar crystals in water kept in a beaker and leave it undisturbed for some time we shall

observe that sugar crystals diffuse into the spaces in between the molecules of water and the sugar is

not visible any more.

Q. Which of the following is matter?

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

Anything that occupies space and has mass is called matter. Matter can exist in three physical

states—solid, liquid, and gaseous.

Chair and almond are forms of matter in the solid state.

Cold drink is a liquid state of matter.

Air is a gaseous state of matter.

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Note: The sense of smell is not matter. However, the smell or odour of a substance is classified as

matter. The smell of any substance (say, perfume) can be classified as matter. This is because,

perfume is in liquid state inside the bottle. It comes out in the form of tiny droplets. These droplets of

perfume are matter and spread out in the atmosphere to create a sense of smell. This smell can be

detected by our olfactory receptors.

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Q. Give reasons for the following observation:

The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food

you have to go close.

The smell of hot sizzling food reaches us several metres away because food particles diffuse faster in

air when hot and we smell it no time whereas cold food particles would take a very long time to

diffuse and we have to go close to have a smell of it.

Q. A diver is able to cut through water in a swimming pool. Which property of matter does this

observation show?

The ability of a diver to cut through water in a swimming pool shows that the particles of matter have

intermolecular spaces. The intermolecular spaces in liquids is fair enough to let the diver pass through

it.

This space is maximum in liquids and gases but minimum in solids and that is why we cannot cut

through a solid.

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

1. Particles of matter have space between them. 2. Particles of matter are continuously moving. 3. Particles of matter attract each other.

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Q. Tabulate the differences in the characteristics of states of matter.

S NO. Solid State Liquid State Gaseous State

1. 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 Compressible to a small extent

Highly Compressible

3. There is little space between the particles of a solid.

These particles have a greater space between them.

The space between gas particles is the greatest.

4. These particles attract each other very strongly.

The force of attraction between liquid particles is less than solid particles.

The force of attraction is least between gaseous particles

5. Particles of solid cannot move freely due to strong force of attraction.

These particles move freely due to weaker force of attractions.

Gaseous particles are in a continuous, random motion.

Q. Define:

1. Rigidity

Rigidity can be expressed as the tendency of matter to resist a change in shape

2. Compressibility

Compressibility is the ability to be reduced to a lower volume when force is applied.

3. Fluidity

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Fluidity is the ability to flow.

4. Kinetic Energy

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

5. Density

The mass per unit volume of a substance is called density (density = mass/volume)

THE SOLID STATE

1. They have definite shape, distinct boundaries and fixed volumes.

2. They have negligible compressibility.

3. Solids are rigid.

4. No diffusion.

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NOTE:

Solids have a tendency to maintain their shape when subjected to outside force. Solids may

break under force but it is difficult to change their shape, so they are rigid.

THE LIQUID STATE

1. Liquids have no fixed shape but have a fixed volume.

2. The rate of diffusion of liquids is higher than that of solids. 3. Liquids flow and change shape, so they are not rigid but can be called fluid. 4. More compressible than solids due to the presence of more space in between particles.

THE GASEOUS STATE

1. Gases are highly compressible as compared to solids and liquids.

2. The rate of Diffusion is higher compared to solids and gases.

3. No fixed shape or volume.

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NOTE:

Liquefied petroleum gas (LPG) cylinder that we get in our home for cooking or the oxygen supplied to

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hospitals in cylinders is compressed gas. Compressed natural gas (CNG) is used as fuel these days in

vehicles. Due to its high compressibility, large volumes of a gas can be compressed into a small

cylinder and transported easily.

Q. Give reasons:

1. A gas fills completely the vessel in which it is kept.

There is little attraction between particles of gas. Thus, gas particles move freely in all

directions. Therefore, gas completely fills the vessel in which it is kept.

2. A gas exerts pressure on the walls of the container 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. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container

3. A wooden table should be called a solid. A wooden table has a definite shape and volume. It is very rigid and cannot be compressed i.e., it has the characteristics of a solid. Hence, a wooden table should be called a solid.

4. We can easily move our hand in air, but to do the same through a solid block of wood, we need a karate expert. 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.

Q. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why. As the volume of a substance increases, its density decreases. Though ice is a solid, it has large number of empty spaces between its particles. These spaces are larger as compared to the spaces present between the particles of water. Thus, the volume of ice is greater than that of water. Hence, the density of ice is less than that of water. A substance with lower density than water can float on water. Therefore, ice floats on water. EFFECT OF CHANGE OF TEMPERATURE

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If we heat cubes of ice in a beaker for some time and measure the temperature we will see that the ice will start melting at a certain temperature but before that it will attain a constant temperature i.e. even if we supply heat energy to it, the temperature shall remain the same. It is because the heat energy supplied is being used up for state conversion. In other words it is used to break the force of attraction between particles of that matter. Q. What happens when heat energy supplied to solids is increased? On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater 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. A stage is reached when the solid melts and is converted to a liquid. The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point. ________________________________________________________________________ NOTE: ________________________________________________________________________

1. The melting point of a solid is an indication of the strength of the force of attraction between its particles. In other words, higher melting point indicates presence of strong force of attraction between its particles which needs a higher temperature (Heat Energy) to be broken.

2. The melting point of ice is 273.16K 3. The process of melting, that is, change of solid state into liquid state is also known as fusion. 4. The temperature at which a liquid starts boiling at the atmospheric pressure is called as its

boiling point.

Q. Define: Latent heat of fusion The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion Latent heat of vaporization The amount of heat energy that is required to change 1 kg of a liquid into vapours at atmospheric pressure at its melting point is known as the latent heat of vaporization. Sublimation Change of state directly from solid to gas without changing into liquid state or vice versa. ________________________________________________________________________

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NOTE: ________________________________________________________________________

1. Particles in steam, that is, water vapours at 373 K (1000 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.

2. State of matter can be changed into another state by changing the temperature. EFFECT OF CHANGE OF PRESSURE

In the above figure we are applying pressure onto the gas present in the cylinder with the help of a piston due to which the inter-particle space reduces and the gas is compressed and is liquefied. I.e. it gets converted into a liquid.

1. Solid Carbon-di-oxide also known as dry ice is stored under high pressure because on decreasing the pressure to 1 atmosphere, it gets converted into gaseous state without coming into liquid state.

2. Pressure and temperature determine the state of a substance, whether it will be solid, liquid or

gas.

3. atmosphere (atm) is a unit of measuring pressure exerted by a gas. The unit of pressure is Pascal (Pa): 1 atmosphere = 1.01 × 105 Pa. The pressure of air in atmosphere is called atmospheric pressure. The atmospheric pressure at sea level is 1 atmosphere, and is taken as the normal atmospheric pressure.

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

During a change of state, the temperature remains constant. This is because all the heat supplied to

increase the temperature is utilised in changing the state by overcoming the forces of attraction

between the particles. Therefore, this heat does not contribute in increasing the temperature of the

substance.

Q. Suggest a method to liquefy atmospheric gases.

By applying pressure and reducing the temperature, atmospheric gases can be liquefied.

Q. Convert the following temperature to Celsius scale:

a. 300 K

b. 573 K

Q. What is the physical state of water at:

a. 250°C

Water at 250°C exists in gaseous state.

a. 100°C

At 100°C, water 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.

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Evaporation

Particles of matter are always moving. At a given temperature in any gas, liquid or solid, there are

particles with different amounts of kinetic energy. In the case of liquids, a small fraction of particles at

the surface, having higher kinetic energy, is able to break away from the forces of attraction of other

particles and gets converted into vapours.

• Evaporation is the conversion of liquid into vapours at any temperature below its boiling point.

FACTORS AFFECTING EVAPORATION

1. an increase of surface area:

If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out

2. an increase of temperature: If the temperature is increased then particles get enough kinetic energy to convert into

vapours.

3. A decrease in humidity

As amount of water vapours present in the environment decreases, less heat energy will be

absorbed by them and it shall increase the rate of evaporation due to the availability of more

heat energy for evaporation.

4. Increase in Wind speed:

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 hereby, making more heat energy available for evaporation. E.g. Clothes dry faster on a windy day.

**Humidity is the amount of water vapours present in air.

Q. How does evaporation cause cooling?

In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy from the

surrounding to regain the energy lost during evaporation. This absorption of energy from the

surroundings make the surroundings cold.

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Q. Why should we wear cotton clothes in summer?

Cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the

atmosphere for easy evaporation. The heat energy equal to the latent heat of vaporisation is

absorbed from the body leaving the body cool.

Q. Why do we see water droplets on the outer surface of a glass containing ice-cold water?

The water vapour present in air, on coming in contact with the cold glass of water, loses energy and

gets converted to liquid state, which we see as water droplets.

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

In a desert cooler, the water inside it is made to evaporate. This leads to absorption of energy from

the surroundings, thereby cooling the surroundings. Again, we know that evaporation depends on the

amount of water vapour present in air (humidity). If the amount of water vapour present in air is less,

then evaporation is more. On a hot dry day, the amount of water vapour present in air is less. Thus,

water present inside the desert cooler evaporates more, thereby cooling the surroundings more. That

is why a desert cooler cools better on a hot dry day.

Q. How does water kept in an earthen pot (matka) become cool during summers?

There are pores on the surface of 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.

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

When we put some acetone or petrol or perfume on our palm, it evaporates. During evaporation,

particles of the liquid absorb energy from the surrounding or the surface of the palm to compensate

for the loss of energy, making the surroundings cool. Hence, our palm feels cold when we put some

acetone or petrol or perfume on it.

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

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. For this reason, we are able to sip hot tea or milk faster from a saucer than a

cup.

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Q. What type of clothes should we wear in summers?

We should wear cotton clothes in summers. During summers, we sweat more. On the other hand,

cotton is a good absorber of water. Thus, it absorbs sweat from our body and exposes the liquid to

the atmosphere, making evaporation faster.

Q. 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 metres away.

(a) Naphthalene undergoes sublimation easily i.e., the change of state of naphthalene from

solid to gas takes place easily. Thus, naphthalene balls disappear with time without leaving any

solid.

(b) Gaseous particles possess high speed and large spaces between them. Particles of perfume

diffuse into these gaseous particles at a very fast rate and reach our nostrils. This enables us to

smell the perfume from a distance.

Q. Give two reasons to justify−

(a) water at room temperature is a liquid.

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

(a) At room temperature (25 °C), water is a liquid because it has the following characteristic of liquid:

(i) At room temperature, water has no shape but has a fixed volume that is, it occupies the shape of

the container in which it is kept.

(ii) At room temperature, water flows.

(b) An iron almirah is a solid at room temperature (25 °C) because:

(i) it has a definite shape and volume like a solid at room temperature.

(ii) it is rigid as solid at room temperature.

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

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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.

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

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.