Process of change of states of matter:
- Vaporization
- Condensation
- Freezing
- Melting
- Sublimation
- Evaporation
Vaporization:(Change of liquid into gas):
The process of change
of water into vapor is called vaporization. When water is heated after reaching
at 1000C water starts boiling. At this temperature water turns into vapor.
Since, water boils at
1000C, hence 1000C is called the boiling point of water.
Boiling points
The common definition
of boiling point is, the temperature at which a liquid boils is called its
boiling point.
Different liquid boils
at different temperatures.
Condensation:(Change of gas into liquid)-
The change of vapor
into water because of decrease in temperature is called condensation. Condensation
is the reverse process of vaporization.When the temperature
of vapor decreases it changes into water, this process is known as
condensation.
Distilled water is
manufactured by the condensation of vapor. The process of making of distilled water
is known as distillation. In distillation first water is boiled to vaporize and
the vapor is cooled, i.e. condensed to get distilled water.
Freezing:(Change of liquid into solid) -
The change of liquid
into solid because of decrease in temperature is called freezing. Water change
into ice because of decrease in temperature, in other words water freezes into
ice because of decrease in temperature. Water freezes at 00C.
Melting:(Change of solid into liquid)
The change of solid
into liquid due to increase in temperature is known as melting. Ice, which is a
solid melts, i.e. changes into water at 00C.
Latent Heat
When water is heated
up-to 1000C it starts boiling and changes into vapor. But we see that even
after continuous supply of heat temperature does not rise above the 100C while
boiling of water.
Temperature supplied
after 100C to boiling water is used to change the water into vapor and
temperature of water does not rise.On the other hand we see that when heat is
supplied to ice, temperature does not rise above the 00C, until all ice melts.
In this process also the heat supplied to ice after 00C is used to change of ice
into water and temperature of ice does not rise.Heat is used in these
processes without rise in temperature is known as Latent Heat.
The latent heat is
used in change of states of matter, such as from solid to liquid or from liquid
to gas without rising in temperature.Hence, Latent heat is the heat released or
absorbed by a body during the process without change in temperature of the
system. This happens while change of state of matter meaning a phase
transition.
Example -
Melting of ice,
boiling of water.
The particles of solid
and liquid are bonded together with great force of attraction, because of which
a matter exists in a particular state. When we supply heat to a solid or
liquid, the heat is supplied without come in notice is used to break the force
of attraction between particles and this heat is not used to increase the
kinetic energy of particles. Since, kinetic energy of particles do not increase
we do not see any rise in temperature of the system.
The word ‘latent’ is
derived from the Latin word ‘Latere” which means “to lie hidden”. Joseph Black
introduced the term Latent heat around 1762.
Types of Latent Heat :
- Latent heat of fusion
- Latent heat of vaporization
1. Latent Heat of Fusion
(Melting or Freezing):
When solid changes
into liquid, the head required changing the state without rising in temperature
is called the Latent Heat of Fusion.
The change of solid to
liquid state is an endothermic reaction as heat is required in it. The reaction
in which heat is supplied or used is called endothermic reaction or process.
Let us take the
example :-
melting of ice.When
heat is supplied to melt ice, temperature does not rise from 00C even
after continuous supply of heat till all ice melts. After melting of all ice
temperature starts rising. The additional heat is required to melt the ice
without coming into notice is the latent heat of fusion.
The latent heat of
fusion of ice is the energy which is used to change the state of ice (solid) to
water (liquid).
The quantity of heat
required to convert I kilogram of solid to liquid without any change in
temperature is called Latent Heat of fusion.
The heat required is
measured in Joules (J).3.34 x 105 joules of heat is required to convert 1 kilogram
of ice into water at its melting point. Thus, the heat of fusion of ice at its
melting point = 3.34 x 105 joules.
2. Latent Heat of
Vaporization:
When liquid changes
into gas because of rise in temperature, the heat required changing the state
without rising in temperature is called the Latent Heat of vaporization.
The change of liquid
to gaseous state is an endothermic reaction as heat is required in it.
Let us take the
example :-
boiling of water.Water
boils at 1000C When heat is supplied to water temperature does not rise after
1000C even after continuous supply of heat. The heat supplied at this stage is
used to change water into vapor and hence does not come into notice. The
additional heat is required to change the water into vapor without coming into
notice is the latent heat of vaporization.
The latent heat of
vaporization of water is the energy which is used to change the state of water
(liquid) to vapor (gas).
22.5
x 105J energy is required to convert 1 kilogram of water into vapor. Hence, the
latent heat of water is equal to 22.5 x 105 J per kilogram or it is written as
22.5 x 105 J/kg.
Different liquid has different latent heat of vaporization.
Sublimation:
The process in which a
solid changes into vapor without changing into liquid and from vapor changes
into solid without changing into liquid is known as sublimation.
Generally solid first
changes into liquid and then changes into gas because of rise in temperature.
But there are many substances, which change into gas without changing into
liquid and changes into solid from gas without changing into liquid. Such
substances, which go under sublimation, are known as sublime.
For example – camphor,
naphthalene balls, ammonium chloride, iodine, dry ice, etc.
1. The solid obtained
after cooling of the gas of sublime is called Sublimate. The process of cooling
of vapor of sublime to get sublimate is also known as ‘sublimation’ although it
is also known as deposition.
2. When camphor is heated
it changes into vapor without changing into liquid. When the vapor of camphor
is cooled it changes into solid without changing into liquid.
Sublimation in
everyday life:
The dry ice (solid
carbon dioxide) turns into vapor without changing into liquid and is considered
as sublime. Because of this property dry ice is used to give the illusion of smoke
or cloud on the stage in movies and stage shows.
Naphthalene balls are
kept with cloths and documents to protect them from insects. Since naphthalene
balls go under sublimation, hence it changes into vapor without changing into
liquid and its vapor prevent the insects to come or stay in cloths or documents.
This protects the documents and cloths to get destroyed.
We usually see that
the size of naphthalene balls decrease gradually and finally disappeared when
they are kept in open. This happens because of sublimation of naphthalene. Naphthalene
balls are used in toilets also as disinfectant and air freshener.
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