INTRODUCTION:
Everything in this universe is made up of material which scientists have
named “matter”. The air we breathe, the food we eat, stones, clouds, stars,
plants and animals, even a small drop of water or a particle of sand– each
thing is matter.
Modern day scientists have
evolved two types of classification of matter based on their physical
properties and chemical nature.
CHARACTERISTICS OF PARTICLES OF MATTER
1. PARTICLES OF MATTER HAVE SPACE
BETWEEN THEM- when we make tea, coffee or lemonade (nimbu paani ), particles of
one type of matter get into the spaces between particles of the other. This
shows that there is enough space between particles of matter. Similarly
particles of sugar, salt, Dettol, or potassium permanganate get
evenly distributed in water.
2. PARTICLES OF MATTER ARE
CONTINUOUSLY MOVING- Particles of matter are continuously moving, that is,
they possess what we call the kinetic energy. As the temperature rises,
particles move faster. So, we can say that with increase in temperature the
kinetic energy of the particles also increases.
3. PARTICLES OF MATTER ATTRACT
EACH OTHER- Particles of matter have force acting between them. This force
keeps the particles together. The strength of this force of attraction varies
from one kind of matter to another.
STATES OF MATTER
1.
THE SOLID STATE- all solids have a definite shape, distinct
boundaries and fixed volumes, that is, have negligible compressibility. Solids
have a tendency to maintain their shape when subjected to outside force. Solids
may break under force but it is difficult to change their shape, so they are
rigid.
2.
THE LIQUID STATE- Liquids have no fixed shape but have a fixed
volume. They take up the shape of the container in which they are kept. Liquids
flow and change shape, so they are not rigid but can be called fluid. The rate
of diffusion of liquids is higher than that of solids. This is due to the fact
that in the liquid state, particles move freely and have greater space between
each other as compared to particles in the solid state.
3. THE GASEOUS STATE- Gases
are highly compressible as compared to solids and liquids. The liquefied
petroleum gas (LPG) cylinder that we get in our home for cooking or the oxygen
supplied to hospitals in cylinders is compressed gas. In the gaseous
state, the particles move about randomly at high speed. Due to this random
movement, the particles hit each other and also the walls of the container.
MATTER CAN CHANGE ITS STATE WATER CAN EXIST IN THREE
STATES OF MATTER–
· Solid, as ice,
· Liquid, as the familiar
water, and
· Gas, as water
vapour.
EFFECT OF CHANGE OF TEMPERATURE
On increasing the temperature of
solids, the kinetic energy of the particles increases. Due to the increase in
kinetic energy, the particles start vibrating with greater speed. The energy
supplied by heat overcomes the forces of attraction between the particles. The
particles leave their fixed positions and start moving more freely. A stage is
reached when the solid melts and is converted to a liquid. The temperature at
which a solid melts to become a liquid at the atmospheric pressure is called
its melting point.
·
The melting point of ice is 273.16 K.
·
The process of melting, that is, change of solid
state into liquid state is also known as fusion.
Solid ----heat----> Liquid -------------------heat-->
Gas
<---cool----
<---cool---------------
So, we infer that the state of
matter can be changed into another state by changing the temperature.
EFFECT OF CHANGE OF PRESSURE
Increasing or decreasing the pressure
can change the state of matter. Applying pressure and reducing temperature
can liquefy gases.
For an example: Solid carbon
dioxide (CO2) is stored under high pressure. Solid CO2 gets converted directly
to gaseous state on decrease of pressure to 1 atmosphere*
without coming into liquid state. This is the reason that solid
carbon dioxide is also known as dry ice.
Thus, we can say that pressure
and temperature determine the state of a substance, whether it will be solid,
liquid or gas.
EVAPORATION: Particles of matter are always moving and are never
at rest. At a given temperature in any gas, liquid or solid, there are
particles with different amounts of kinetic energy. In the case of liquids, a
small fraction of particles at the surface, having higher kinetic energy, is
able to break away from the forces of attraction of other particles and gets
converted into vapour. This phenomenon of change of a liquid into vapours at
any temperature below its boiling point is called evaporation.
FACTORS AFFECTING EVAPORATION
The rate of evaporation increases
with–
• An increase of surface area: We know that evaporation is a surface
phenomenon. If the surface area is increased, the rate of evaporation
increases. For example, while putting clothes for drying up we spread them out.
• An increase of temperature: With the increase of temperature, more
number of particles get enough kinetic energy to go into the vapour state.
• A decrease in humidity: Humidity is the amount of water vapour
present in air. The air around us cannot hold more than a definite amount of
water vapour at a given temperature. If the amount of water in air is already
high, the rate of evaporation decreases.
• An increase in wind speed: It is a common observation that clothes
dry faster on a windy day. With the increase in wind speed, the particles of
water vapour move away with the wind, decreasing the amount of water vapour in
the surrounding.
HOW DOES EVAPORATION CAUSE COOLING?
In an open vessel, the liquid
keeps on evaporating. The particles of liquid absorb energy from the
surrounding to regain the energy lost during evaporation. This absorption of
energy from the surroundings make the surroundings cold.
After a hot sunny day, people
sprinkle water on the roof or open ground because the large latent
heat of vaporisation of water helps to cool the hot surface.
Why should we wear cotton
clothes in summer?
During summer, we perspire more
because of the mechanism of our body which keeps us cool. We know that during
evaporation, the particles at the surface of the liquid gain energy from the
surroundings or body surface and change into vapour. The heat energy equal to
the latent heat of vaporisation is absorbed from the body leaving the
body cool. Cotton, being a good absorber of water helps in absorbing the sweat
and exposing it to the atmosphere for easy evaporation.
Why do we see water droplets on
the outer surface of a glass containing ice-cold water?
Let us take some ice-cold water
in a tumbler. Very soon we see water droplets on the outer surface of
the tumbler. The water vapour present in air, on coming in contact
with the cold glass of water, loses energy and gets converted to liquid state,
which we see as water droplets.
Paper Compiled by : Mr. Pawan Kumar Jangra
(M.Sc., B.Ed. D.I.S.M., A.C.M)
Mob. : 9464317615, 9888018092, 9815388137
e- mail: pkjangra2011@gmail.com
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