Interconversion of States of Matter


Matter can change from one form to other form i.e from solids to liquids to gases.
The phenomenon of the change of matter from one state to another and back to original state is known as interconversion of the sates of matter.
Matter can be changed from one state to another by changing temperature or pressure.

Change in state of water:  When heat energy is supplied to ice it changes into water and then to vapor. If we cool the steam it gets converted into water and further cooling of water changes into ice.
Here the heat energy is used up in changing the state of matter. the heat is used to increase the kinetic energy of the particles of ice to such an extent that they break away from the rigid lattice structure of the solid form, ice, and move around freely to form the liquid form, water. So, until all the ice has melted, the heat absorbed does not raise the temperature of the ice-water mixture. This heat, which does not raise the temperature of the body, is called Latent Heat.

Melting or Fusion: Melting is the process where solid changes into a liquid at a particular temperature.

Melting point:  The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.

Melting points of some solids:

            Solids         Melting point
Ice (H2O) 00C
Sodium chloride(NaCl) 8000C
Iron 15350C

Latent heat:  The word 'latent' means hidden. The characteristic amount of energy absorbed or released by a substance during a change in its physical state that occurs without changing its temperature is known as latent heat.

Latent heat of fusion :  Latent heat of fusion is the amount of heat energy required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point.

Boiling: Boiling is the process where a liquid  changes into a vapour at a particular temperature.

Boiling point:   Water boils at 1000C. At that temperature, it changes from the liquid state to the gaseous state. The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point

Boiling points of some liquids:

               Liquid            Boiling point
Water  1000C
Chloroform 620C
Sulphuric acid 2800C

Latent heat of vaporization:  Latent heat of vaporization is the amount of heat energy required to change 1 kg of liquid into a gas at atmospheric pressure at the boiling point.

Freezing:  The process, where a liquid converts into a solid, is called freezing or solidification.
On cooling a liquid the particles come closer due to the decreased kinetic energy.When the particles come closer the inter particular spaces are reduced and the forces of attractions  increased. Finally the particles are arranged themselves in a regular, compact manner. 

Evaporation:  The process where a liquid changes into vapor at any temperature below its boiling point is evaporation .Evaporation is a surface phenomenon. i.e evaporation takes place at the surface of the liquid.

Factors affecting evaporation:

  • Surface area
  • Temperature
  • Humidity and
  • Wind speed.

Rate of evaporation: Surface area
The rate of evaporation increases with an increase of surface area. When the surface area is more, evaporation will be faster.
For example shallow quarries or bunds are built near the sea. The shallow bunds provide a relatively large surface area for water to evaporate quickly, Water from these bunds evaporates, leaving salt behind. Then the salt is collected and refined before use. 

Rate of evaporation: Temperature
The rate of evaporation increases with an increase of temperature.
Cloths dry faster on a sunny day than on a cloudy day

Rate of evaporation: Effect of Humidity
The rate of evaporation increases with decrease in humidity.

Rate of evaporation: Effect of Wind
The rate of evaporation increases with an increase in wind speed.
The water vapour particles in atmosphere move away with the winds. This results in a decrease of the amount of water vapour in the surroundings. Due to this reason, clothes dry faster on a windy day than a normal day.

Evaporation cause cooling:
During the process of evaporation, the particles of liquid absorb energy from the surroundings, to regain energy lost during evaporation. This absorption of energy from the surroundings makes the surroundings cold.

Differences between boiling and evaporation:

                             Boiling                                           Evaporation       
It is a rapid process. It is a slow process.
It is takes place at the entire mass of the liquid. It takes place at the surface of the liquid.
It takes place at any temperature. It takes place at specific temperature called the boiling point of the liquid.
It cause cooling i.e the substance becomes cool due to evaporation. The temperature of the liquid remains constant during boiling process.

Condensation:  The process where vapor changes to a liquid is called condensation.
Example: The water vapour condenses and we receive the same water in the form of rain.
When you pour cold water in a glass. You will  observe the formation of  water droplets on the outer surface of the glass . This is due to the condensation of water vapour present in atmosphere.

Sublimation:  The process, where a solid, on heating, directly changes into gas without changing into liquid, and a gas, on cooling, directly changes to solid without changing into liquid is called sublimation 

Example: solid ammonium chloride, on heating directly converts into vapors without changing to the liquid state. These vapors get condensed to the solid state by condensation process.
The sublimation of Naphthalene and camphor can take place without heating them. They sublimes at room temperature.

Liquification process:  A gas is liquefied by applying high pressure and reducing the temperature.
Example: petroleum gas is liquefied by applying high pressure and reducing the temperature to liquefied petroleum gas(LPG).
This principle is used in the liquification of air to separate the components of air.


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