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7 March 2015

Properties of liquid states

Properties of liquid states
Properties of liquid states

Properties of liquid states


Evaporation 

The process in which the liquid state changes into the gaseous state is called evaporation.

Explanation: When the molecules of the liquid gained the kinetic energy from the surrounding then the kinetic energy of some molecules become high enough to break the intermolecular force and enter into the gaseous state is known as evaporation.


Factors of evaporation

  1. Intermolecular forces: If the intermolecular forces of any liquid is weak then the evaporation will be faster.
  2. Temperature: If the temperature of increase then the evaporation is increase as the kinetic energy of molecules is increase and move quickly.
  3. Surface area: If the surface area is increased then the evaporation is also increased that’s why china dish is used rather than a beaker in laboratory.

Vapour pressure

The pressure at which the rate of evaporation and rate of condensation become equal is called vapour pressure.

Explanation: When liquid evaporates in a closed container then the evaporated molecules start gathering over the liquid surface. At the same time the molecules lose kinetic energy and condense slowly to return back to the liquid. After sometime the rate of condensation is increased and the stages come when the rate of evaporation and rate of condensation become equal this is known as vapour pressure.

Factors of vapour pressure

  1. Intermolecular forces: The liquid having weak intermolecular forces will have high vapour pressure.
  2. Temperature: if the temperature is increased then the vapour pressure is also increased.

Boiling Point

The temperature at which the vapour pressure of a liquid becomes equal to the atmospheric pressure or any external pressure is called boiling point.

Or

The temperature at which the liquid state changes into the gaseous state is called boiling point.

Exp: When the liquid is heated its molecule gained kinetic energy and break the intermolecular forces and evaporates. As evaporation increases the vapour pressure is also increased and a stage comes when the rate of vapour pressure becomes equal to the atmospheric pressure or any other pressure this is called boiling point. Boiling point of a liquid can be increased or decreased by changing the external pressure.

Example: In pressure cookers boiling point of a water is increased above 100°C thus at higher temperature cooking time of meat and pulses is reduced.

 

Molar heat of vapourization

When a liquid reaches the boiling point then the further heating does not increase or rise the temperature but just continue to vapourize thus it is defined as “The amount of heat that required to vapourize one mole of a liquid at its boiling point is called molar heat of vapourization”.

Example: heat of vapourization for one mole of water is 40.7 KJ/mole

 

Application or uses of boiling point

Its major uses is that it is used for the separation of different liquid on its boiling point. Such as different constituent of petroleum are separated or purified on the basis of boiling point.


Freezing point

The temperature at which the liquid state is changes into the solid state is called freezing point.

Exp: The melting point and freezing point of a substance are always same. Both melting and freezing of water is 0°C. Melting, freezing and boiling point shows the strength of a substance if these are high then the substance will have strong bond.


Diffusion in liquid

 The molecules of liquid are always moving continuously that’s why another molecule spread in it very easily through the process of diffusion. The diffusion of gases is faster than the diffusion in liquid.

Example: A drop of ink spread in a glass of water very easily the process of diffusion. It also depends on temperature as temperature is increased then the speed of molecule is also increase and diffusion is also increased.


                           Temperature α Speed of molecules or diffusion


 Density of liquid

The mass per unit volume of any substance is called density.


Exp: The density of liquid is greater than the density of gases due to strong intermolecular forces between their bonds and it depends on temperature as the temperature is increased the density is decreased.


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