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The States of Matter

Updated on July 15, 2017

Anything having mass and occupies space is called matter.
States of Matter
There are three states of matter:
1) Solid
It has definite shape and volume e.g. wood, steel etc.
2) Liquid
It has definite volume but not a definite shape e.g. water, oil etc.
3) Gas
It has neither definite shape nor definite volume e.g. air, oxygen etc.
Kinetic Molecular Theory of Matter:
According to Kinetic Molecular Theory (KMT), all matter is composed of tiny particles called molecules which are always in motion and posses Kinetic Energy. The three states of matter depend on:
Arrangement of molecules
Motion of molecules
Attractive forces between molecules
Kinetic Description of Solid State
Molecules are closely packed with each other
They only posses vibrational motion
Molecules cannot slip or slide over one another hence posses definite shape and volume
Kinetic Description of Liquid State
Molecules are loosely packed and can move in all directions.
Kinetic energy of molecules is less than gaseous state
Intermolecular forces are more than gases therefore posses constant volume
Kinetic Description of Gaseous State
Molecules are lying away from one another
Attractive forces are negligible between molecules therefore they can move in all direction very easily
Molecules posses high Kinetic energy hence they have neither definite shape nor definite volume

Three States of Matter


Inter Conversion of Three States

Fusion or Melting:
The process of conversion of Solid state into Liquid state is called Fusion or Melting
On heating solid is converted to liquid. Heat increases the kinetic energy of the particles and they start vibrating at higher frequency. At a particular temperature the vibrational motions become fast that they overcome the cohesive forces and solid melts to liquid.
Melting Point:
The temperature at which the solid is converted to liquid on heating is called melting point.
Boiling or Vaporization:
The process of conversion of Liquid state into Gaseous state is called Boiling or Vaporization.
When liquid is heated, Kinetic energy of molecules increase and molecules start escaping from the surface of the liquid in the form of vapours or gas.
Boiling Point
The temperature of a liquid at which its vapour pressure becomes equal to the atmospheric pressure is called boiling point.
The conversion of some solids directly into gaseous state on heating is called sublimation. Iodine, ammonium chloride and naphthalene change directly into vapour state upon heating.
The movement of molecules from a higher concentration to a lower concentration is known as Diffusion.
The spreading of a substance through a medium like air or water is called diffusion.
Diffusion in Gases
Gases diffuse rapidly as it depends upon density or molar mass of a substance. The molecules of one gas can diffuse easily into the molecules of other gas. For example if an open bottle of a perfume is kept in a room, its smell will spread uniformly throughout the room.
Graham’s Law of Diffusion
Thomas Graham, in 1833 studied the rate of diffusion of different gases and gave graham’s law.
“The rate of diffusion of a gas is inversely proportional to the square of its molar mass or density.”
“Lighter gas can diffuse faster than the heavier one.”
Diffusion in Liquids
Liquid molecules can also diffuse because they have free movement. Since the molecules of liquid move comparatively slowly than gas molecule, their rate of diffusion are also lesser than gases.
Brownian movement
Robert Brown (1927) discovered this phenomenon:
“The free movement of the molecules of gases and liquid is called Brownian Movement.”
“A continuous, rapid, zigzag motion of suspended particles through the medium is called Brownian Motion.”

Mix some powdered sulphur in water and stir it.
After stirring filter the solution. Some very small sulphur particles will remain in the filtrate.
Now put a drop of filtrate on a slide and examine it under high powered microscope.
It is observed that sulphur particles perform Brownian motion.

Brownian movement Example



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