Page 19 - Understanding NCERT Science 09

are some that change directly from solid state enclosed in a cylinder? Will the particles come
to gaseous state and vice versa without closer? Do you think that increasing or
changing into the liquid state. decreasing the pressure can change the state
of matter?
Activity _____________1.13

• Take some camphor. Crush it and put
it in a china dish.
• Put an inverted funnel over the china
dish.
• Put a cotton plug on the stem of the
funnel, as shown in Fig. 1.7.

Fig. 1.8: By applying pressure, particles of matter
can be brought close together

Applying pressure and reducing
temperature can liquefy gases.
Have you heard of solid carbon dioxide
(CO )?It is stored under high pressure. Solid
2
CO gets converted directly into gaseous state
2
on decrease of pressure to 1 atmosphere*
without coming into liquid state. This is the
Fig. 1.7: Sublimation of camphor reason that solid carbon dioxide is also known
as dry ice.
• Now, heat slowly and observe. Thus, we can say that pressure and
• What do you infer from the above temperature determine the state of a
activity?
substance, whether it will be solid, liquid
or gas.
A change of state directly from solid to gas
without changing into liquid state is called
sublimation and the direct change of gas to
solid without changing into liquid is called
deposition.

1.4.2 EFFECT OF CHANGE OF PRESSURE
We have already learnt that the difference in
various states of matter is due to the Deposition
difference in the distances between the
constituent particles. What will happen when
we start putting pressure and compress a gas Fig. 1.9: Interconversion of the three states of matter

* atmosphere (atm) is a unit of measuring pressure exerted by a gas. The unit of pressure is Pascal (Pa):
5
1 atmosphere = 1.01 × 10 Pa. The pressure of air in atmosphere is called atmospheric pressure. The
atmospheric pressure at sea level is 1 atmosphere, and is taken as the normal atmospheric pressure.

8 SCIENCE

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