9th science

Matter In Our Surroundings

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. (Solid → Liquid)
  • A liquid changes into gas by increase in temperature. (Liquid → Gas)
  • Gas changes into liquid by decrease in temperature. (Gas → Liquid)
  • liquid changes into solid by decrease in temperature. (Liquid → Solid)


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.

Ice → Water → Vapour

On decrease in temperature vapor changes into water. On further decrease in temperature water changes into ice.

Vapour → Water → 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.

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 (Thrity two degree Fahernheit) has been defined for the freezing point of water.

2120F (Two hundred tweleve degree Fahrenheit) has been defined for the boiling point of water. Fahrenheit was replaced by Celsius.

Degree Celsius: The unit of Celsius is named after the Swedish Astronomer Anders Celsius, who developed a similar scale. Untill 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.

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

Conversion Formulae

Celsius to Fahrenheit: `[\ ^0F]=[\ ^0C]xx9/5+32`

Fahrenheit to Celsius: `[\ ^0C]=([\ ^0F]-32)xx5/9`

Celsius to Kelvin: `[K]=[\ ^0C]+273`

Kelvin to Celsius: `[\ ^0C]=[K]-273`