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Everything
in the universe is made up of matter.
Matters occupy
space and have mass. i.e., they have
·
Mass: SI unit of mass is kilogram (kg).
·
Volume:
SI unit is cubic metre (m3).
The common unit of measuring volume is litre (L).
1L = 1 dm3, 1L = 1000 mL, 1 mL = 1 cm3.
Early Indian philosophers classified matter as five basic elements (Panch Tatva) - air, earth, fire, sky & water.
Ancient Greek philosophers had a similar classification.
In modern science, there are 2 types of classification of matter based on physical properties & chemical nature.
PHYSICAL NATURE OF MATTER
MATTER
IS MADE UP OF PARTICLES
There were two schools of thought regarding the nature of matter.
1. Matter is continuous like a block of wood.
2. Matter is made up of particles like sand (particulate).
Experiment to show the nature
of matter:
•
Fill a 100 ml beaker halfway with water.
•
Dissolve
some salt/ sugar.
•
The water level
does not change.
• Salt/ sugar particles break and spread throughout water filling the spaces between water particles.
HOW SMALL ARE THESE PARTICLES OF MATTER?
The particles of matter
are very small.
It can be proven by
following experiment:
•
Dissolve 2–3
crystals of potassium permanganate (KMnO4) in 100 mL of
water.
•
Transfer 10 mL of this solution into 90 mL of
clear water.
•
Transfer 10
mL of this solution into another 90 mL of clear water.
•
Keep
diluting the solution 5 to 8 times.
• The water is still coloured (light colour).
-
It shows
that a few crystals of KMnO4 can colour a large volume of water
(about 1000 L). i.e., each KMnO4 crystal contains millions of tiny
particles. It divides into smaller and smaller particles.
- This activity can be done using 2 ml of Dettol. The smell can be detected even on repeated dilution.
CHARACTERISTICS OF PARTICLES OF MATTER
PARTICLES
OF MATTER HAVE SPACE BETWEEN THEM
-
Particles of
sugar, salt, Dettol, or KMnO4 evenly distribute in water.
- In tea,
coffee or lemonade, particles of one type of matter get into spaces between
particles of the other.
-
It shows
that there is space between particles of matter.
PARTICLES
OF MATTER ARE CONTINUOUSLY MOVING
Experiment 1:
•
An unlit
incense stick can be smelled only if we go very close to it.
•
When it is
lit, the smell can be felt from a distance.
Experiment 2:
•
Take two
glasses/beakers filled with water.
•
Put a drop
of blue or red ink slowly along the sides of the first beaker and honey in the
second beaker.
•
The ink
spreads faster evenly throughout the water within minutes. For honey, it takes
hours.
Experiment 3:
•
Drop a
crystal of copper sulphate or KMnO4 into a glass of hot water and
another containing cold water. Do not stir the solution.
•
In cold
water, the crystals settle at the bottom. In hot water, it slowly spreads
showing blue/ purple colour.
• As time
passes, the hot water turns blue/purple. But in cold water, there is no
significant color change.
The above experiments show that:
o Particles of matter are continuously moving, i.e.,
they possess kinetic energy. As the temperature rises, kinetic energy
increases (particles move faster).
o
Particles can intermix by getting into the spaces
between them. Intermixing of particles of two different types of matter is
called diffusion. On heating, diffusion becomes faster due to increase
in kinetic energy.
PARTICLES
OF MATTER ATTRACT EACH OTHER
- Particles of matter are held together by force
of attraction. Strength of force of attraction varies in different types of
matter. E.g.,
•
Breaking
an iron nail, a piece of chalk, and a rubber band. Iron nails are difficult to
break due to greater force of attraction between iron particles.
• Water has a weak attraction force than solids. So it is easy to cut the water using fingers. When fingers are withdrawn it joins again.
STATES OF MATTER
Matter exists in 3 states: solid, liquid and gas.
1. THE
SOLID STATE
-
Solids have
a definite shape, distinct boundaries and fixed volumes. Show negligible
compressibility.
-
E.g., pen,
book, needle, wooden stick etc.
- Solids maintain
their shape when subjected to outside force. They may break under force but changing
shape is difficult. So they are rigid.
-
A rubber
band changes shape under force and regains the same shape when the force is
removed. If excessive force is applied, it breaks. So rubber band is a solid.
-
When sugar
and salt kept in different jars, they take the shape of the jar. But
these are solids because each sugar or salt crystal has fixed shape.
-
Sponges are also solid. But it can be compressed due to the presence of
air-filled holes. When it is pressed, the air is expelled out.
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 is called fluid.
-
E.g., water,
cooking oil, milk, juice, cold drinks etc.
-
Solids, liquids
and gases can diffuse into liquids. The atmospheric gases diffuse and dissolve
in water.
-
Rate of
diffusion in liquids is higher than in solids because liquid particles move
more freely and have more space between them compared to solid particles.
3. THE
GASEOUS STATE
Gases are highly compressible as compared to solids &
liquids. It can be shown by the following experiment.
•
Take
three 100 mL syringes and close their nozzles by rubber corks.
•
Remove the
pistons of all syringes.
•
Leave one
syringe empty, fill the second with water, and add pieces of chalk to the third.
•
Apply some
Vaseline on the pistons (for smooth movement) and insert into the syringes.
•
Try to
compress the content by pushing the piston in each syringe.
•
The piston
in the syringe with air can be easily pushed because gas is highly compressible.
-
Due to
high compressibility, large volumes of a gas can be transported in a small
cylinder. E.g.,
·
Liquefied
petroleum gas (LPG) cylinder.
·
Oxygen cylinder in hospitals.
·
Compressed
natural gas (CNG) is used as fuel in vehicles.
·
Helium
gas cylinder is used to fill balloons.
-
The rate
of diffusion of gases is higher than that of solids &
liquids. It is due to high speed of particles and large space between them. By
this, gases diffuse very fast into other gases. E.g., particles of the aroma of
food mix with air particles and reach us quickly.
- In gaseous state, the particles move randomly at high speed. As a result, the particles hit each other and the walls of the container. The pressure of the gas is due to this force exerted by gas particles per unit area on the walls of the container.
CAN MATTER CHANGE ITS STATE?
-
Water can
exist in three states of matter: solid (ice), liquid (water) and gas
(water vapour).
-
Temperature and pressure determine the state of a substance.
EFFECT OF CHANGE OF TEMPERATURE
•
Take about
150 g of ice in a beaker and suspend a thermometer so that its bulb is in
contact with the ice.
•
Heat the beaker on a low flame.
•
The temperature when the ice starts melting is 0° C.
•
The temperature when all the ice has converted into
water (liquid state) is still 0° C.
• Now stir the water with a glass rod till the water starts boiling and vapourising (gaseous state). Temperature increases and reaches 100° C.
-
On
increasing the temperature of solids, kinetic energy of the particles
increases. As a result, the particles vibrate faster. The energy supplied by heat
overcomes the forces of attraction between the particles allowing them to move
freely. Thus the solid state changes into liquid state. It is called melting
(fusion).
-
The
minimum temperature at which a solid melt to become a liquid at the atmospheric
pressure is called its melting point. It indicates the strength of the
force of attraction between its particles.
-
The
melting point of ice is 273.15 K.
Kelvin: SI unit of temperature. 0°
C =273.15 K (≈ 273 K).
Kelvin to Celsius: Subtract 273 from the
given temperature.
Celsius to Kelvin: Add 273 to the given
temperature.
-
During the
melting of a solid (e.g., ice), its temperature does not change after the
melting point is reached, till all the solid melts.
-
Ice (solid)
absorbs heat energy without increasing its temperature, which is used to change
the state by overcoming the forces of attraction between particles. This is
called latent heat.
- The heat energy needed to change 1 kg of a
solid into liquid at atmospheric pressure at its melting point is called the latent
heat of fusion.
-
So,
particles in water at 0° C (273 K) have more energy as compared to particles in
ice at the same temperature.
-
When heat
energy is supplied to water, the particles move faster. At a certain temperature,
they gain enough energy to overcome the forces of attraction and the liquid
starts changing into gas. The temperature at which a liquid starts boiling at
the atmospheric pressure is called its boiling point.
-
Boiling is
a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to
change into vapour.
-
Boiling
point of water is 373 K (100°C).
-
The heat
energy needed to change 1 kg of a liquid into gas at atmospheric pressure at
its boiling point is called the latent heat of vaporisation.
- Particles in steam (water vapour) at 373 K have more energy than water at the same temperature because the steam particles have absorbed extra energy as latent heat of vaporization.
Sublimation
and Deposition
- The direct
change of solid to gas without changing into liquid state is called sublimation.
E.g., camphor.
-
The direct
change of gas to solid without changing into liquid is called deposition.
E.g., camphor.
Experiment:
•
Crush some
camphor 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.
•
Heat slowly.
Camphor changes directly from solid to gas. This gas condenses on the upper
part of the funnel.
EFFECT
OF CHANGE OF PRESSURE
-
Difference in states of matter is due to the difference
in the distances between the particles.
-
Change in
pressure can change the state of matter.
-
When pressure
is exerted and compress a gas in a cylinder, the particles come closer. Gases liquefy
on applying pressure and reducing temperature.
- Solid carbon dioxide (CO2) is stored under high pressure. When pressure is decreased to 1 atmosphere, it transforms into gaseous state without coming into liquid state. So it is also known as dry ice.
Atmosphere (atm) is a unit
of measuring pressure exerted by a gas.
1 atmosphere = 1.01 × 105
Pascal (Pa - unit of pressure).
The atmospheric pressure
(pressure of air in atmosphere) at sea level
is 1 atmosphere (normal atmospheric pressure).
EVAPORATION
-
It is the change
of a liquid into vapour at any temperature below its boiling point
(i.e., without reaching the boiling point). E.g., Water, when exposed, slowly changes
into vapour, wet clothes dry up etc.
-
Particles of
matter are always moving. In liquids, some surface particles with higher
kinetic energy can overcome the forces of attraction and escape as vapour.
FACTORS AFFECTING EVAPORATION
•
Surface
area: Evaporation is a surface phenomenon. Increasing
the surface area increases the rate of evaporation. E.g.,
o Water taken in an open China dish evaporates
faster than in a test tube.
o Spreading wet clothes helps to dry up fast.
• Temperature: As temperature increases, more particles get enough kinetic energy increasing evaporation.
•
Humidity: Humidity is the amount of water vapour present in air. The air can
only hold a certain amount of water vapor at a given temperature. High humidity
decreases the rate of evaporation.
•
Wind
speed (velocity): As the wind speed increases, the
particles of water vapour move away with the wind. It decreases the amount of surrounding
water vapour. That’s why clothes dry faster on a windy day.
HOW DOES EVAPORATION CAUSE COOLING?
-
In an open
vessel, the liquid keeps on evaporating.
-
The liquid
particles absorb energy from the surrounding to regain the energy lost during
evaporation. This makes the surroundings cold.
-
When acetone
(nail polish remover) is poured on palm, the particles gain energy from the
palm or surroundings and evaporate. It causes the palm to feel cool.
-
After a
hot 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?
-
In summer,
we perspire more to keep the body cool.
- During evaporation,
the particles at the surface of the sweat 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 is
a good absorber of water. So it absorbs sweat and exposes it to the atmosphere
for easy evaporation.
Why do we see water
droplets on the outer surface of a glass containing ice-cold water?
When water vapor in the air contacts a cold glass of water, it loses energy and condenses into liquid droplets.
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