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| 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
- Intermolecular forces: If
the intermolecular forces of any liquid is weak then the evaporation will be
faster.
- Temperature: If the temperature
of increase then the evaporation is increase as the kinetic energy of molecules
is increase and move quickly.
- 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
- Intermolecular forces: The
liquid having weak intermolecular forces will have high vapour pressure.
- 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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