ZEBAR SCHOOL FOR CHILDREN

Std. IX – Science (2025-26)

Ch- 1- Matter in our Surroundings Notes

Name: ____________________ Std / Sec: ____ Roll No. _____ Date________

Characteristics of Particles of Matter

Particles of matter have space between them
→ Gas can be compressed a lot because of the space between their particles.
Particles of matter attract each other because of force of attraction
→ Force of attraction between particles of matter keeps the particles bonded together. The force of
attraction between particles of solid is greatest, between particles of liquid is moderate and
between particles of gas is lowest.
The force of attraction between particles of solid, liquid and gas can be arranged in decreasing
order as follows: Solid > Liquid > Gas
Particles of matter are continuously in motion
→ Liquids and gases can flow because particles are in motion. Particles of matter are continuously
moving as they possess kinetic energy, with the increase of temperature kinetic energy of particles
also increases so particle moves faster.
Characteristics of states of matter:
• Solid State
1.The space between the particles is negligible/very less.
2. The force of attraction between the particles is strong. Thus, particles in a solid are closely
packed.
3. Solids maintain their shape even when they are subjected to external force i.e., they are rigid.
4. Solids cannot be compressed.
5. The kinetic energy of the particles is very less and so solids have an orderly arrangement of the
particles. Therefore, solids have a fixed shape and volume.
• Liquid State
1. The space between the particles is slightly more as compared to solids, but still very less as
compared to gases. The particles of a liquid can slip and slide over each other.
2. The force of attraction between the particles is strong enough to hold the particles together but
not strong enough to hold the particles in a fixed position.
3. Liquids do not have a fixed shape but have a fixed volume. Liquids take up the shape of the
container in which they are poured.
4. The kinetic energy of the particles is more than that of solids. Thus, liquids have a disorderly
arrangement of particles compared to solids.
5. Liquids cannot be compressed much. The compressibility of liquids is almost negligible.
• Gaseous State
1.The particles are much farther apart from one another as compared to solids and liquids. They
have a very disorderly arrangement of particles compared to the solids and liquids.
2. The force of attraction between the particles is negligible, hence particles of a gas move freely in
all the directions. Gases thus can mix or diffuse into other gases.
3.The particles of a gas have maximum kinetic energy. They move with high speed in all directions
and can exert pressure on the walls of its container.
4. Gases neither have a definite shape nor a definite volume. They fill up the container completely.
5. Gases can be compressed easily. Example: the LPG cylinders used at home and the CNG
cylinders used in vehicles.

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LATENT HEAT
(Why does temperature remain constant while melting/boiling?)
Latent heat is the heat supplied to overcome the forces of attraction between the particles of
the substance during the change of state. Energy must be supplied to a substance to melt it or to
boil it, i.e. to change its state. This energy does not increase the temperature of the substance. It
does not increase the kinetic energy of the particles of the substance so the temperature does not
rise. This heat utilized in changing the state of the substance is called latent heat.
Latent heat of fusion-
The amount of heat required to convert 1 kg of a substance from the solid state to liquid state at 1
atmosphere pressure and at its melting point without any change in temperature.
The latent heat of fusion of ice is 336 joules/gram.
Latent heat of vapourization-
The amount of heat required to convert 1 kg of a substance from the liquid state to gaseous state at
1 atmosphere pressure and at its boiling point without any change in temperature.
The latent heat of vapourization of water is 2260 joules/gram.
1 calorie = 4.186 joules.
MELTING- The process of change from solid state to liquid state at a particular temperature.
BOILING- The process of change from liquid state to gaseous state at a particular temperature.
MELTING POINT- The temperature at which a solid melts to become a liquid at 1 atmosphere
pressure.
BOILING POINT- The temperature at which a liquid starts changing into gas at 1 atmosphere
pressure.
SUBLIMATION- The process in which a substance changes directly from solid state to gaseous
state, without passing through the intermediate liquid state.
e.g. dry ice (solid CO2), iodine, naphthalene, camphor etc.
DESUBLIMATION- Desublimation is the reverse process of sublimation. The process in which a
substance changes directly from the gas to the solid state, with no intermediate liquid state.
When these solids are heated their particles move so quickly that they separate completely to form
vapour. When these vapours are cooled, these particles slow down so quickly that they become
fixed and form a solid.
EFFECT OF CHANGE OF PRESSURE ON STATES OF MATTER
When a gas is compressed, the particles will come closer to each other and inter molecular force of
attraction increases. As a result, the gas changes into liquid state.
e.g. Butane gas (a component of petroleum) is compressed so as to change into liquid state and
filled in cooking gas cylinders as L.P.G. (Liquefied Petroleum Gas)
e.g. Gaseous CO2 changes into solid CO2 when temperature is reduced to about -78.4OC and
pressure is 1 atmosphere. Solid CO2 is called dry ice as it resembles ice and used for cooling but
does not turn into liquid state and wet the surface as dry ice (solid CO2) undergoes sublimation and
changes into gaseous state above −78.4 °C and at 1 atmosphere pressure.
ANOMALOUS EXPANSION OF WATER
Density of water changes with temperature in a unique way. Normally in other liquids, volume of
liquid decreases on cooling (volume decreases as temperature decreases), so density of the liquid
increases. But when water is cooled it first contracts upto 4OC i.e. its volume decreases with
decrease in temperature. And when we further reduce the temperature from 4OC to 0 OC, it starts
expanding instead of contracting and continues to expand till it reaches 0OC, where it freezes into
solid ice. This is known as anomalous expansion of water. Thus, water has maximum density at
4OC and least at 0OC. As ice is lighter than water, it floats on water.
The anomalous expansion of water plays an important role in the survival of aquatic animals
during severe winters. Ice being lighter and a bad conductor of heat forms an insulating layer over
the water body and prevents the cooling of underlying water, which remains warm.
FACTORS AFFECTING EVAPORATION:
1. Surface area- If the surface area increases, the rate of evaporation increases.
e.g. liquid taken in a plate evaporates faster than when taken in a cup.
2. Temperature- If the temperature increases, the rate of evaporation increases as more number of
particles get enough kinetic energy to change its state to vapour.

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 e.g. Clothes dry faster on a hot summer day than in winter or on a cloudy day.
3. Humidity- If the humidity (amount of water vapour in the air) increases the rate of evaporation
decreases, as the air cannot hold any more water vapour at a given temperature.
e.g. Clothes dry faster on a dry day than on a wet (rainy) day.
4. Wind speed- If the wind speed increases, the rate of evaporation increases as the particles of
water vapour move away with the wind. e.g. We feel relief under a fan when we perspire.

BOILING EVAPORATION
The process in which a substance changes When a substance changes its state from
its state from liquid to gas at a particular liquid to gas at any temperature below its
temperature. e.g. boiling point of water is boiling point.
100oC
It is a rapid and a visible process. It is a slow and an invisible process.
Boiling happens throughout the liquid. (bulk Evaporation happens only at the surface.
phenomena) (surface phenomena)
Boiling of a liquid does not produce a cooling Evaporation produces a cooling effect. It
effect. The temperature of the liquid remains leads to a decrease in temperature of the
constant during boiling and the temperature liquid and the surroundings.
of the surrounding increases.
During this process there is no change in the During this process there is a variation in the
temperature. temperature.
Formation of bubbles occurs during boiling. There is no formation of bubbles in
evaporation.

In-text questions Page no. 3

1. Which of the following are matter?
chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
A: chair, air, smell, almonds, and cold-drink, smell of perfume
(Sense of smell is not matter but smell of any substance is matter)
2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell
from cold food you have to go close.
A. Kinetic energy of the particles of matter increases with increase in temperature. Rate of
diffusion in gases is very high. Hot sizzling food gives out vapours which diffuse faster in air
and thus we can smell it easily from a distance. Whereas cold food particles due to the low
kinetic energy would take a very long time to diffuse and we have to go closer to smell it.
3. A diver is able to cut through water in a swimming pool. Which property of matter does
this observation show?
A. Because of –
a) State of water in a pool is liquid.
b) Presence of intermolecular space in water.
c) Intermolecular force of attraction in water or any liquid is weak hence the diver's force is
enough to overcome these forces.
4. What are the characteristics of the particles of matter?
A. a) They have intermolecular space between the constituent particles.
b) They are moving continuously and possess kinetic energy.
c) They have intermolecular force of attraction between the particles.
In-text questions Page no. 6
1. The mass per unit volume of a substance is called density.
(density = mass/volume).
Arrange the following in order of increasing density: air, exhaust from chimneys, honey, water,
chalk, cotton and iron.
A: Increasing density: air < exhaust from chimneys < cotton < water < honey < chalk < iron

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2. (a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container,
shape, kinetic energy and density.
(a) Difference in the characteristics of 3 states of matter.

CHARACTERISTICS SOLIDS LIQUIDS GASES

arrangement of particles are particles are loosely particles are far apart/
molecules tightly/ closely packed separated from each
packed other by wide spaces
inter molecular force of very high/ less as compared to very less/ least/
attraction maximum solids minimum
intermolecular space very less/ least/ more than solids, less very high/ maximum
minimum than gases
vibration of particles particles vibrate at particles can move particles can move
their mean within their boundary randomly
position
shape have a definite do not have definite no definite shape
shape shape. they take the
shape of the container
volume have definite have definite volume no definite volume
volume
boundaries have distinct have distinct no distinct boundaries
boundaries boundaries
hardness/ rigidity very hard and not hard and rigid not hard and rigid
rigid
fluidity do not flow flow in a particular flow randomly in all
direction (high to low) directions
compressibility not compressible not compressible highly compressible
density generally high generally low density generally very low
density density
rate of diffusion very low more than solids, less very high
than gases
storage can be stored cannot be stored can be stored in a
without a vessel without a vessel closed vessel only
kinetic energy least intermediate very large/very high
expansion on heating very low/ less intermediate high capacity to expand
on heating

(b) Rigidity- It is the property of matter to resist the change in its shape.
Compressibility- It is the property of matter in which its volume is decreased by applying force.
Fluidity- It is the ability of matter to flow.
Filling a gas container- On filling a gas, it takes the shape of the container and the individual
particles being far away fill up the entire container.
Shape- Having definite boundaries.
Kinetic energy- It is the energy possessed by the particles of matter due to its motion.
Density- It is the ratio of mass per unit volume.

3. Give reasons:
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood we
need a karate expert.

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A. a) Gases have the least/negligible intermolecular force of attraction and very high kinetic energy.
As a result these particles move randomly in all directions, so they fill up the vessel completely in
which they are kept.
b) Gases have very high kinetic energy. Hence gases have random motion in all directions. So,
freely moving particles of gas hit the walls of the container continuously and this exerts pressure on
the walls of the container.
c) A wooden table is hard and rigid; it has a definite shape and volume. It cannot be compressed-
as it has the characteristics of a solid it is classified as a solid.
d) Air is a mixture of gases. Inter molecular space in gases is maximum and least/negligible
intermolecular forces of attraction. So, we can move our hand easily through air.
But a solid block of wood is hard and rigid. Intermolecular space in solids is the least i.e.
particles are closely packed and they have strong inter-molecular forces of attraction. So, we need a
karate expert to apply external force through a solid block of wood to break it.
4. Liquids generally have lower density as compared to solids. But you must have observed that
ice floats on water. Find out why.
A: Due to anomalous expansion, water has maximum density at 4OC and least at 0OC. So, the
molecules in ice (at 0OC)make a cage like structure with lot of vacant spaces. Thus, as ice is lighter
than water, it floats on water.

In-text questions Page no. 9

1. Convert the following temperature to Celsius scale: (a) 300 K (b) 573 K
A. (a) 300 – 273 = 27°C (b) 573 – 273 = 300°C
2. What is the physical state of water at: (a) 250°C (b) 100°C
A: (a) 250°C = gas (b) 100°C liquid as well as gas
3. For any substance, why does the temperature remain constant during the change of state?
A: During the change of state of any matter heat is supplied to the substance. As this heat is utilized
to overcome the force of attraction between the particles, at this period of time, temperature
remains constant. This extra heat acquired by the molecules in the form of hidden heat is called
latent heat and is utilized to change from one state of matter to the other state.
4. Suggest a method to liquefy atmospheric gases?
A. The atmospheric gases are taken in a cylinder with piston fitted on it. By cooling and applying
pressure on them, the gases can be liquefied.

In-text questions Page no. 10

1. Why does a desert cooler cool better on a hot dry day?
A1. On a hot dry day, temperature is high and humidity is low, so the rate of evaporation of water
from the khus screens of the cooler is high. The evaporating water takes heat equal to latent heat of
vapourization from the air inside the cooler thus causing a cooling effect. As the rate of evaporation
is high, the amount of heat taken up also is more. Thus, the fan fitted in the desert cooler throws this
cool air in the room giving a good cooling effect.
2. How does the water kept in an earthen pot (matka) become cool during summer?
A. An earthen pot has fine holes and small droplets of water come out from it. They take up the
heat equal to latent heat of vapourization from the surface and convert into vapour. This
evaporation of water through the fine holes in the earthen pot makes it cool.

3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?
A. When a liquid evaporates, the particles of the liquid absorb energy equal to latent heat of
vapourization from the surrounding and make it cool. On applying acetone/petrol/perfume on our
palm we feel cold because it starts evaporating at a low temperature by taking the energy equal to
latent heat of vaporization from our palm, leaving it cool.
4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
A. A saucer has a larger surface area than the cup. Larger the surface area higher is the rate of
evaporation due to which tea/milk cools rapidly.
5. What type of clothes should we wear in summer?

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A. During summer we should wear cotton clothes because during summers we sweat more. Cotton
being porous, cotton clothes are good absorbers of water. Hence they absorb sweat rapidly and
evaporate it by absorbing heat equal to latent heat of vapourization from our body. Due to which
our body feels cool.

In-text questions Page no. 12

1. Convert the following temperatures to the Celsius scale.
(a) 293 K (b) 470 K.
A: (a) 293 K into °C 293 – 273 = 20°C (b) 470 K into °C 470 – 273 = 197°C
2. Convert the following temperatures to the Kelvin scale.
(a) 25°C (b) 373°C.
A: (a) 25°C into K 25 + 273 = 298 K (b) 373°C into K 373 + 273 = 646 K
3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
A. (a) Naphthalene balls undergo sublimation at room temperature due to which it converts directly
into vapour state (gas) from solid state without leaving any residue.
(b) When sprayed, vapours from the perfume diffuse in air very fast at room temperature. These
vapours have very high kinetic energy and high rate of diffusion, hence move randomly in all
directions so we can smell them, sitting several metres away.
4. Arrange the following substances in increasing order of forces of attraction between the
particles—water, sugar, oxygen.
A. oxygen —> water —> sugar
5. What is the physical state of water at—(a) 25°C (b) 0°C (c) 100°C
A. (a) 25°C is liquid (b) 0°C is solid and liquid (c) 100°C is liquid and gas
6. Give two reasons to justify:
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
A. (a) Water at room temperature is a liquid because its freezing point is 0°C and boiling point is
100°C. (b) An iron almirah is a solid at room temperature because melting point of iron is higher
than room temperature. At this temperature, iron has a definite shape and volume. It is hard ,rigid
and incompressible.
7.Why is ice at 273 K more effective in cooling than water at the same temperature?
A. Water at 273K or 0OC has absorbed heat energy equal to the latent heat of fusion from the
surroundings. Whereas ice at the same temperature has not absorbed heat. Hence, ice is more
effective in cooling than water at the same temperature.
8. What produces more severe burns, boiling water or steam?
A. Steam at 373K or 100OC has absorbed heat energy equal to the latent heat of vapourization.
Whereas water at the same temperature has not absorbed heat. Hence, steam produces more
severe burns than boiling water.
9. Name A, B, C, D, E and F in the following diagram showing change in its state.
A. A —> liquefication/melting B —> vapourisation /evaporation C—>condensation D—> solidification
E —> sublimation F —> deposition/desublimation

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