Chapter-1:
Matter In Our Surroundings
Topics To be covered:
1) Interconversion of states of matter
2) Effects of change of temperature
(i) Melting(Fusion) (ii) Boiling
(iii) Condensation(Liquefaction) (iv) Freezing
(v) Sublimation (vi) Deposition
3) Effects of change of pressure
1.Interconversion of states of matter
The change in physical state by altering the
physical factors such as temperature and pressure
is called physical change.
On increasing temperature, interparticle space
increases and interparticle force of attraction
decreases, resulting into the change in state from
solid to liquid and liquid to gas. On decreasing
the temperature, reverse process occurs.
On increasing pressure, interparticle space
decreases and interparticle force of attraction
increases, resulting into the change in state from
liquid to solid and gas to liquid. On decreasing
the pressure, reverse process occurs.
2. Effects of change of temperature
(i) Melting(Fusion): The change of state from solid to liquid at
a fixed temperature is called melting or fusion.
The temperature at which any solid substance melts and
changes into liquid at atmospheric pressure is called its melting
point.
Different substances have different melting points due to
different forces of attraction among their constituent particles.
Impurities decreases the melting point of solids.
Temperature remains constant during melting as heat energy
supplied is all used up in overcoming the force of attraction
between its particles without increasing the kinetic energy of
the particles and hence change of state occurs.
The amount of heat required to change one kg of solid into
liquid without changing its temperature is called latent heat of
fusion.
To demonstrate that the temperature
remains constant during the melting
A beaker was taken and some ice cubes were put into
it.
A thermometer was kept in the beaker such that its
bulb touched the ice.
Heating was started and temperature was recorded
when ice started melting and even when all ice got
converted into water.
It was found that the temperature remained constant
during the change of state.
The supplied heat got utilized in overcoming the force
of attraction between the particles and hence, no net
change in temperature was observed in thermometer.
(ii) Boiling: The change of state from liquid to vapour or gas
at a fixed temperature is called boiling.
The temperature at which vapour pressure becomes equal
to the atmospheric pressure is known as boiling point.
Different liquids have different boiling points due to
different forces of attraction among their constituent
particles.
Impurities increases the boiling point of liquids.
Temperature remains constant during boiling as heat energy
supplied is all used up in overcoming the force of attraction
between its particles without increasing the kinetic energy
of the particles and hence change of state occurs.
The amount of heat required to change one kg of liquid into
vapour or gas without changing its temperature is called
latent heat of vapourisation.
To demonstrate that the temperature
remains constant during the boiling
A beaker was taken and 100mL of water was poured into
it.
A thermometer was kept in the beaker such that its bulb
should be dipped in it.
Heating was started and temperature was recorded when
water started boiling and even when most of the water got
vapourised.
It was found that the temperature remained constant
during the change of state.
The supplied heat got utilized in overcoming the force of
attraction between the particles and hence, no net change
in temperature was observed in thermometer.
(iii) Condensation(Liquefaction): The process in
which a gaseous state is converted into liquid state
by lowering down its temperature.
It is the reverse phenomenon of vapourisation.
(iv) Freezing: The change of liquid state into solid
state is known as freezing.
The temperature at which liquid gets converted
into solid at atmospheric pressure is called
freezing point.
(v) Sublimation: The process in which a solid
directly converts into gaseous state on heating
without changing into liquid state.
The solids which can show the sublimation are
called sublime.
The examples of substances which show
sublimation are camphor, iodine crystals, dry ice,
ammonium chloride, naphthalene balls, etc.
(vi) Deposition: The process in which gaseous state directly
converts into solid on cooling without changing into liquid
state.
The solids which are obtained by the process of deposition
are called sublimate.
3. Effects of change of pressure
Pressure also plays an important role along with the
temperature in changing the physical state of a matter.
On increasing pressure, gas particles come close to one
another. When these particles come closer, the force of
attraction comes into picture and the gaseous state changes
into liquid state.
When some more pressure is applied the liquid state further
changes into solid state.
There is a little or negligible impact of pressure on liquids
and solids.
Home Work
1.Why is heat needed to melt a solid?
2.Why is it advised that the iodised salt should be
stored in airtight containers?
3.Give appropriate reasons to justify:
(i)Food cooks faster in a pressure cooker.
(ii)Ice cubes cause more cooling sensation as compared
to zero degree Celcius water.
(iii)Steam produces more severe burns than boiling
water does.
4.Why does the temperature of a substance remain
constant during the change of its state?
5.Explain the effect of increasing pressure and
decreasing temperature on a gas.
6.Define latent heat of fusion? Write the value of latent
heat of fusion of ice.
7. Account for the following:
(i)After a hot shower, your bath room mirror is covered
with water.
(ii) Naphthalene balls kept in stored warm clothes
disappear over a period of time.
8.Can boiling point be used as a criterion of purity of a
substance? Explain with one example.
9.What is the difference between a gas and a vapour.
Give two examples.
10.What is dry ice? Why it is called so?
11.Out of sodium chloride and ammonium chloride
which can be purified by sublimation?
