Change of States of Matter
Matters can be changed
from one state to another state. A solid can be changed into liquid and a liquid
can be changed into gas. Most of the metals, which are solid, turn into liquid
on heating and turn into vapor on further heating.
The change of state of
matters depends upon mainly two factors:
- Temperature
- Pressure
Effect of temperature on states of matter:
- Solids change into liquid with increase in temperature.
- A liquid changes into gas by increase in temperature.
- Gas changes into liquid by decrease in temperature.
- liquid changes into solid by decrease in temperature.
Example - Ice is
solid, water is liquid and vapour is gas.
On increase in
temperature ice changes into water. On further increase in temperature water
changes into vapor.
On decrease in
temperature vapor changes into water. On further decrease in temperature water
changes into ice.
On heating the
particles of a solid get more kinetic energy and they start moving rapidly. On
the other hand heating increases the space between the particles. When the kinetic
energy of particles and space between them become similar to the liquid, the
matter fulfills the condition of arrangement of particles. In this condition a
solid changes into liquid.
On heating the
particles of a liquid gets more kinetic energy and they start moving more
rapidly. The increase in temperature increases the kinetic energy of particles
and inter-space between them increases. The increase in kinetic energy and
space between the particles the force of attraction between particles
decreases. When the kinetic energy of particles of liquid and space between the
particles increases and force of attraction between them decreases enough, the
particles of liquid start moving with great speed. In this condition the
particles of liquid attain the arrangement similar to gas and liquid changes
into gas.
Water (a liquid)
changes into ice (a solid) at 00C. Water changes into vapour (a gas) at 1000C.
The change of solid to
liquid is called melting. The change of liquid to gas is called the
vaporization. This happens because of increase in temperature.
The change of gas into
liquid is called condensation. The change of liquid into solid is called freezing.
These takes place because of decrease in temperature.
Effect of pressure:
Solid –There is no effect of pressure on solids.
Solids are non
compressible, i.e. solids cannot be compressed as there is no space between
their particles which could allow compression.
When the pressure is
increased on a solid, it is deformed and finally broken.
Liquid – There is no effect on pressure on liquid.
Liquids are non
compressible, i.e. liquids cannot be compressed since there is not enough space
between their particles to get compressed.
Gas – The volume of gas decreases with increase in pressure.
Since there is lot of
space between the particles, gas is highly compressible. Large volume of gas
can be compressed to a small volume. Because of this nature high
compressibility, gas is transported easily after compressed to a small volume
in cylinders.
Natural gas is
compressed to small volume and packed in cylinders. It is used widely as fuel
to running vehicles. Because of compression it is called Compressed Natural Gas
or simply known by CNG (Compressed Natural Gas).
Oxygen is compressed
and packed in small cylinders, which is used to save life in hospitals.
On increasing more
pressure gas turns into liquid.
THE LIQUEFACTION OF GAS BY INCREASING OF PRESSURE:
In general condition,
the particles of gas are far from each other. They move independently and
rapidly in all directions. There is lot of space between the particles of gas.
The force of attraction is negligible between the particles of gas. Because of
these characters gas can be compressed a lot.
When pressure is
applied on the gas, its particles come closer to each other. After applying
high pressure, the particles of gas come very close to each other that they
start attracting each other. The space between the particles of gas also
decreases with increase in pressure. While applying high pressure a lot of heat
is evolved, which was using by the particles of gas in movement. So, while
applying high pressure to compress the gas, temperature is keeping low to
overcome with the heat released. As they come closer, they lose kinetic energy.
Finally they get closely packed at a certain high pressure, at this stage they
get bonded with each other and turned into liquid.
This process is called
liquidation or liquefaction of gas.
Petroleum Gas is
compressed to small volumes. At more pressure it turns into liquid, after that
it is packed into cylinders. This is used widely as fuel to cook food in
households. Compressed petroleum gas is commonly known as LPG (Liquefied
Petroleum Gas) since it turns into liquid form.
Oxygen, hydrogen,
nitrogen, helium, etc. are compressed to liquefy and used for many purposes.
Liquefied oxygen is used as propellant in spacecraft rockets. Liquefied oxygen
is used for industrial and medical purposes also. Liquefied oxygen is of blue
color.
On further increase in
pressure, gas turns into solid.
Carbon dioxide is gas
turns into solid on high pressure. Solid carbon dioxide is known as dry-ice. It
is also known as ‘Cardice’ or ‘Card ice’.
Dry ice is used in the
storage of food.
On decrease in
pressure liquefied gas turns into gas. Solid carbon dioxide (dry ice) turns
into gas without changing into liquid on decrease in pressure and increase of
temperature.
Unit of Temperature:
Temperature is
measured in Degree Celcius, Fahrenheit and Kelvin.
1. Fahrenheit: Before the end of 20th century Fahrenheit was used as unit to
measure the temperature. The scale of Fahrenheit was named after, the physicist
Daniel Gabriel Fahrenheit. Fahrenheit is written as “0F” and read as degree
Fahrenheit.
320F (Thirty
two degree Fahrenheit) has been defined for the freezing point of water.
2120F (Two
hundred twelve degree Fahrenheit) has been defined for the boiling point of
water. Fahrenheit was replaced by Celsius.
2. Degree Celsius: The unit of Celsius is named after the Swedish Astronomer Anders
Celsius, who developed a similar scale. Until 1948 Celsius was known as
Centigrade. The word centigrade comes after the Latin word ‘Centum’.
Degree Celsius is
written as “0C” and read as degree Celsius.
00C (zero
degree Celsius) has been defined for the freezing point of water.
1000C
(hundred degree Celsius) has been defined for the boiling point of water.
Degree Celsius is
replaced by Kelvin. Moreover, it is used widely even today in clinical as well
as laboratory thermometer.
3. Kelvin: Kelvin is the SI unit of temperature. The symbol of Kelvin is
‘K’. The Kelvin scale is named after the physicist William Thomson, 1st Baron
Kelvin.
The scale of Kelvin is
used widely because of its many advantages over degree Celsius. In Kelvin
temperatures are written in positive usually.
273 K is defined as
the freezing or melting point of ice.
373 K is defined as
the boiling point of water.
At Kelvin scale -273 K
is considered as the absolute zero temperature.
Degree Celsius -
Degree Fahrenheit - Kelvin
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