Matter

MatterAnything which occupies space and have mass is called a matter. Everything in the world is made up of matter. Air, water, stones, food, plants, animals whereas our universe is made up of matter…!!

matter

Physical Nature of Matter- Matter is made up of particles

Matter is made up of particles. In other words, everything is made up small particles. These particles which make up all the matter around us are called atoms or molecules.

The matter is made up extremely small particles which cannot be seen even with a powerful microscope. What we actually see is an aggregate of tiny particles. For example, even a drop of water contains about 1021 molecules of water.

How small are these particles

Experiment

Experiment

1.2 Characteristics of Particles of Matter

Particles of matter get into the spaces between particles of the

other. This shows that there is enough space between particles of

matter. The particles of gases have large gap between each other

and the particles of liquid have gap less than that of gases and more

than that of solids between them and whereas particles of solids

have least space between them.

1.2.1 Particles of matter have space between them

The particles of matter attract each other. In other words, particles of matter have a force acting between them. This force keeps the particles together. The strength of this force of attraction, however, differs from one kind of matter to other. To illustrate the strength of this force of attraction, take an iron nail, a piece of chalk and a rubber band. Try to break each one of them by hammering, cutting or stretching. You will observe that it is most difficult to break the iron nail, somewhat easier to break a piece of chalk and easiest to break a rubber band. Thus, the particles of iron rod are held together by the strongest force followed by the piece of chalk while particles of rubber band are held together by the strongest force followed by the piece of chalk while particles of rubber band are held

together by the weakest forces of attraction.

1.2 Characteristics of Particles of Matter

1.2.2 Particles of matter attract each other

1.3 States of Matter

Properties –

i. Solids have definite shape.

ii. Solids have distinct boundaries.

iii. Solids have fixed volume.

iv. Solids have negligible compressibility.

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

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

Types of Solids1. Crystalline Solids (diamond, copper sulphate etc.)

2. Amorphous Solids (rubber, sponge etc.)

The Solid State

Properties –

i. Liquids have don’t have a fixed shape. They attain the shape of the container in which they are kept.

ii. Liquids flow and change their shape, so they are not rigid but can be called fluid.

iii. Solids, gases and liquids can diffuse into liquids.

iv. Solids don’t have tendency to maintain shape when subjected to outside force.

v. Liquids have a definite volume at a given temperature.

vi. Liquids are almost incompressible.

1.3 States of MatterThe Liquid State

o Properties-i. Gases do not have definite shape.

ii. They do not have a definite volume too.

iii. Gases also have a tendency to flow as liquids do. Therefore, they are also considered as fluids.

iv. Gases diffuse very easily among other substances at a considerable rate.

v. The interspace between their molecules is maximum while the attraction force is the minimum. Therefore, the gas molecules occupy all the space available to them.

vi. The density of gases is minimum.

vii. Gases exert pressure on the walls of the container, in which they are filled. This pressure is due to the random movement of particles and hitting against the walls of the container.

1.3 States of MatterThe Gaseous State

1.4 Can Matter Change its State

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 great 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. Melting Point : The temperature at which a solid melts to become liquid at the atmospheric temperature is called its melting point. The melting point of a solid is an indication of the strength of the force of attraction between its particles. The melting point of ice is 273.16 K. Fusion : The process of melting, that is, change of solid state into liquid states also known as fusion.

1.4.1 Effect of change of temperature

When a solid melts, its temperature remains the same, so where does the heat energy go?

During the experiment of melting, that the temperature of the

system does not change after the melting point is reached, till all

the ice melts. This happens even though we continue to heat the

beaker, that is, we continue to supply heat. This heat gets used up

in the changing the state by overcoming the forces of attraction

between the particles. As this heat is absorbed by ice without

showing any rise in temperature. It is considered that it gets

hidden into the contents of the beaker and is known as latent

heat.

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 latent heat of fusion.

1.4 Can Matter Change its State1.4.1 Effect of change of temperature

When we supply heat energy to water, particles start moving even

faster. At a certain temperature, a point is reached when the

particles have enough energy to brake free from the forces of

attraction of each other. At this temperature the liquid starts

changing into gas.

Boiling Point : The temperature at which a liquid starts boiling at the atmospheric temperature is known as its boiling point. Boiling is a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to change into the vapour state.

For water this temperature is 372 K { 100°C = 273+100 = 373 K }

Particles in steam, that is, water vapour at 373 K (100°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 vaporisation.

1.4 Can Matter Change its State1.4.1 Effect of change of temperature

The state of matter can be changed into another by changing the

temperature.

We have learnt that substances around us change state from solid

to liquid and from liquid to gas on application of heat. But there

are some that change directly from solid state to gaseous state

and vice versa without changing into the liquid state.

1.4 Can Matter Change its State1.4.1 Effect of change of temperature

The difference in various states of matter is due to the difference in the distances between the constituent particles. Applying pressure and reducing temperature can liquefy gases. Solid carbon dioxide is stored under high pressure. Solid carbon dioxide gets converted directly to gaseous state without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.

Thus, we can say that pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas

1.4 Can Matter Change its State1.4.1 Effect of change of pressure

By applying pressure, particles of matter can be brought close together

Evaporation

Particles of matter are always moving and are never at rest. At a given temperature in any gas, liquid or solid there are particles with different amounts of kinetic energy. In the case of liquid, 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 phenomenon of converted into vapour. This phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.

Factors affecting Evaporation

Temperature: By rising temperature, the rate of evaporation also increases.

Surface Area: Rate of evaporation can be effected by increasing and decreasing the surface area.

Humidity: When humidity increases the rate of evaporation decreases.

Speed of wind: Wind need kinetic energy to flow. If the speed of wind will be more than the kinetic energy and temperature will be also more, so the rate of evaporation will be also more.

Nature of liquid: The rate of evaporation also depends on the nature of liquid, i.e. the interparticle force of attraction.

Why should we wear cotton clothes in summer?

During summer, we perspire more because of the mechanism of our body which keeps us cool. We know that during evaporation, the particles at the surface of the liquid gain energy from the surroundings or body surface and change into vapour. The heat energy equal to the latent heat of vaporisation is absorbed from the body leaving the body cool. Cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation.

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

cold water?

Let us take some ice-cold water in a tumbler. Soon we will see water droplets on the outer surface of the tumbler. The water vapour present in air, on coming in contact with the cold glass of water, looses energy and get converted to liquid state, which we see as water droplets.

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