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TNPSC CHEMISTRY (ENGLISH)

WHAT IS KINETIC THEORY OF MATTER?

Anything that occupies space and possesses weight is termed matter. The amount of matter contained in any object is known as its mass.

All matter (whether solid, liquid or gaseous) consist of extremely small particles (atoms or molecules) which are capable of independent existence. The main differences between the three states of matter (solid, liquid or gas) involve:

(i) The state of aggregation (or packing) of the molecules,

(ii) The amount of kinetic energy possessed by the molecules, and

(iii) The magnitude of the attractive forces between the molecules.

The molecules of a gas are in continuous random motion and exert pressure on the walls of the container. The kinetic energy of the gas molecules increases with the increase in temperature.

 

Solid: Solids  are characterized by definite shape, size and volume.  In solids, the molecules ae very closely arranged because the force of attraction between the molecules is very strong.  They are incompressible.  Fourth state of matter - plasma super heated gaseous state.  Fifth state of matter Bose –Einstein condensate – super cooled Solids.

Liquid: Liquids occupy definite volume but have no definite shape.  It takes the shape of the containr.  The force of attraction between the molecules in a liquid is less when compared to solids, and these molecules are loosely packed.  This allows the liquid to change its shape easily.  They are negligibly compressible.  A few examples for matter that exist in liquid state are water, oil, juice etc.,

Gas: The atoms or molecules of matter that always occupies the whole of the space in which they are contained is called a gas. It neither occupies a definite volume nor possesses a definite shape.  The force of attraction between the molecules of a gas is negligibly small, because themolecules are very loosely packed.  The molecules are distributed at random throughout the whole volume of the container.  Gases are ighly compressible when compared to solids and liquids.  The Liquefied Petroleum Gas (LPG) cylinder that we get in our home for cooking or the oxygen supplied to hospitals in cylinders are compressed gases.  Compressed Natural Gas (CNG) is used as fuel these days in vehicles, too.

 

Properties of Solid, Liquid and Gas:
 

S.No

Solid              

LIQUID

GAS

1

Have definite shape and volume

Have definite volume but no definite shape

Have neither definite shape nor definite volume

2

Cannot flow

Can flow from higher level to lower level

Can flow very easily and quickly

3

Intermoleculare space is minimum

Intermolecular space is moderate

Intermolecular forces is maximum

4

Intermolecular forces are maximum

Intermolecular forces are less

Intermolecular forces are negligible

5

They are incompressible

They are compressible to an extent

They are easily compressible

 

Effect of temperature on Solid, Liquid and Gas:

Water can exist as three states of matter.

✦ Solid, as ice

✦ Liquid, as water

✦ Gas, as water vapour

The temperature at which a solid melts to become a liquid is called its  melting point. The temperature at which a liquid starts boiling is known as its boiling point.

Changes that take place around us are of two types

✦ Physical changes

✦ Chemical changes

 

Physical changes

This process of converting solid directly into its vapour state is known as sublimation.when an electric current is passed through the filament of a bulb, the filament starts glowing and there is a change in the appearance of the filament.  When the current is cut OFF the glow of bulb stops and its original appearance is restored.

A solid can change into liquid on heating.  For example, ice melts into water on being heated.  This process is called melting.

If this liquid (water) continues to be heated, it changes into vapour.  This process is called evaporation.

The vapour, when allowed to cool, condenses into its liquid state.  This process is called condensation.

This water, when cooled further changes to ice.  This process is called freezing.

 

Chemical Changes:

In the presence of moisture, iron reacts with oxygen present in ari, to form hydrated ‘iron oxide’, known as rust.  Oxygen and water are two essential ingredients for rusting  of iron; absence of either or both of them can prevent rusting.

Burning of a candle is an example of a chemical change.  Wax molecule is converted into carbondioxide and water molecules.

                                                 Magnesium + oxygen Magnesium Oxide

If you collect the ash and mix it well with a small amout of water, another new substance is formed.

                                                Magnesium + oxygen + water Magnesium Hydroxide

Phenolic compounds are responsible for the bright colours, aroma and flavor of many fruits and vegetables.  They have been shown to reduce the risk of heart disease and certain types of cancer.

Vegetables and fruits turn brown on cutting due to the reaction between the phenolic compound in fruits and the oxygen in the air.  Phenolic compound and oxygen react to form a brown pigment known as melanin.

If you have any objects made from silver you know that the bright, shiny surface of silver gradually darkens and becomes less shiny.  This discolouration known as tarnishing.  This happens because silver undergoes a reaction with sulphur contained in the air.

 

Iron Pillar

In New Delhi, near Qutub Minar, stands an iron pillar which is more than 7 meters tall and weighs more than 6000 kg.  it was built 1600 years ago.  Strangely, even after such a long period of time it has not rusted.  Scientists from all over the world have examined its quality of rust resistance.  It shows the advances India had made in metal technology as far back as 1600 years ago.

Ships are made of iron.  A part of a ship always remains under water.  Since the sea water contains a great amount of salt, the ship suffers a lot of damage from rusting in spite of being painted.  These rusted parts need to be replaced every now and then.

Prevention of rusting can be done by

Applying oil, paint or grease

✦ Galvanisation (deposition of zinc over iron)

✦ Chrome plating (deposition of chromium over iron)

✦ Tinning (coating of tin over iron)

 

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