In this article, we will quickly revise the key concepts of "Matter in Our Surroundings." Matter is anything that occupies space and has mass. It exists in three primary states: solid, liquid, and gas. Solids have a fixed shape and volume, while liquids take the shape of their container but have a fixed volume. Gases have neither a fixed shape nor a fixed volume. The states of matter can change due to temperature and pressure variations, leading to processes like melting, evaporation, condensation, and sublimation. The kinetic energy of particles plays a vital role in these changes. The concept of diffusion explains how particles mix with one another in different states of matter. Understanding these properties helps us in everyday applications, from cooking to industrial processes. If you Want PDF Scroll down the Page.
Chapter – 1 Matter in Our Surroundings
Matter is anything that has mass and occupies space. Based
on this definition, let's categorize the given items:
Matter
(Has mass and occupies space):
·
Chair
·
Air
·
Almonds
·
Lemon water
Not
Matter (Does not have mass or occupy space):
·
Love (An emotion)
·
Hate (An emotion)
·
Thought (A mental process)
·
Smell (A sensory perception)
·
The smell of perfume (A perception, but the perfume itself is matter)
·
Cold (A temperature condition, not a substance)
·
Give reasons for the following
observation:
Que -2 The smell of hot sizzling food reaches you several
meters away, but to get the smell from cold food, you have to go close.
·
The smell of hot sizzling food
reaches you from several meters away because heat increases the kinetic energy
of the food's molecules, causing more volatile aromatic compounds to evaporate
and diffuse into the air. These airborne molecules then spread rapidly due to
increased air movement and convection currents.
·
In contrast, cold food releases
fewer volatile molecules since the lower temperature reduces their evaporation.
As a result, the smell does not travel as far, requiring you to be closer to
detect it.
3. A diver is able to cut through water in a swimming
pool. Which property of matter does this observation show?
This observation shows that matter is made up of
particles with spaces between them. The diver can move through the
water because the particles of water have spaces between them, allowing them to
move aside and let the diver pass.
4. What are the characteristics of the particles of matter?
The characteristics of the particles of matter are:
1.
Made up of tiny
particles – Matter is composed of extremely
small particles that cannot be seen with the naked eye.
2.
Have space between them – There are gaps between the particles, which allow matter to mix
and diffuse.
3.
Constantly in motion – Particles of matter are always moving; their speed increases with
temperature.
4.
Attract each other – Particles exert forces of attraction on one another, which hold
them together. The strength of this force varies in different states of matter
(solid, liquid, gas).
Page - 6
1. The mass per unit volume of a substance is called density. (density=mass/volume). Arrange the following in the order of increasing density – air, exhaust from the chimneys, honey, water, chalk, cotton and iron.
To arrange the given substances in increasing order of
density, we consider their general densities:
1.
Air – Least dense
2.
Exhaust from chimneys – Mostly gases, slightly denser than air
3.
Cotton – Very low density due to air trapped between fibers
4.
Water – Standard density (1 g/cm³)
5.
Honey – Denser than water due to dissolved sugars
6.
Chalk – A solid with moderate density
7.
Iron – Most dense among the given substances
Final
order (increasing density):
Air < Exhaust from chimneys < Cotton <
Water < Honey < Chalk < Iron
2.
Answer the following
a)
Tabulate the differences in the characteristics
of matter.
|
Characteristic |
Solid |
Liquid |
Gas |
|
Shape |
Fixed |
Takes
shape of container |
No
fixed shape, fills container |
|
Volume |
Fixed |
Fixed |
No
fixed volume, expands to fill container |
|
Compressibility |
Very
low |
Low |
High |
|
Particle
Arrangement |
Closely
packed |
Loosely
packed |
Very
loosely packed |
|
Intermolecular
Forces |
Strongest |
Moderate |
Weakest |
|
Kinetic Energy |
Lowest |
Moderate |
Highest |
|
Fluidity |
Does
not flow |
Flows |
Flows
freely |
|
Density |
High |
Moderate |
Low |
b)
Comment upon the following: rigidity,
compressibility, fluidity, filling a gas container, shape, kinetic energy
and density.
Here's a brief comment on each property:
1.
Rigidity: It is the property of a substance to retain its shape and resist
deformation. Solids exhibit high rigidity due to strong intermolecular forces,
whereas liquids and gases have low rigidity.
2.
Compressibility: This refers to the ability of a substance to decrease in volume
under pressure. Gases are highly compressible due to the large spaces between
particles, while solids and liquids have very low compressibility.
3.
Fluidity: The ability of a substance to flow. Liquids and gases exhibit
fluidity because their particles can move past each other, whereas solids lack
fluidity due to strong intermolecular forces.
4.
Filling a Gas Container: Gases completely occupy the volume of their container due to weak
intermolecular forces and high kinetic energy, allowing particles to move
freely in all directions.
5.
Shape: Solids have a definite shape due to strong intermolecular forces,
while liquids take the shape of the container they are in, and gases do not
have a fixed shape, spreading to fill any available space.
6.
Kinetic Energy: It refers to the energy possessed by particles due to their
motion. Gases have the highest kinetic energy, followed by liquids, and then
solids, where particles vibrate in fixed positions.
7.
Density: It is the mass per unit volume of a substance. Solids generally
have the highest density, followed by liquids, and then gases, which have the
lowest density due to the large spaces between their particles.
3.
Give reasons
a)
A gas fills completely the vessel in which it
is kept.
When a gas fills the vessel completely, it means the gas
particles are spread throughout the entire volume of the container, regardless
of the shape or size of the vessel. This behavior is explained by the kinetic
molecular theory, which states that gas molecules are in constant random motion
and will expand to fill any available space.
In terms of properties:
·
The gas molecules are spread
out and occupy all the space in the container.
·
The pressure exerted by the gas
on the walls of the vessel is uniform throughout.
·
The temperature of the gas is
related to the average kinetic energy of the particles.
This behaviour is true for ideal gases, where interactions
between gas molecules are negligible and they are assumed to occupy the entire
volume available.
b)
A gas exerts pressure on the walls of the
container.
Yes, a gas exerts pressure on
the walls of its container due to the collisions of gas molecules with the
container's surfaces. Gas molecules are in constant motion, and when they
collide with the walls, they transfer momentum. This transfer of momentum generates
a force on the container walls, which, when spread over the area of the
container, results in pressure.
Pressure is defined as force per
unit area, and in the case of a gas, the pressure depends on factors such as
the temperature, volume, and the number of gas molecules. According to the
ideal gas law (PV = nRT), the pressure is directly proportional to the
temperature and the number of molecules, and inversely proportional to the
volume.
c)
A wooden table should be called a solid.
It seems like you're suggesting
that a wooden table should be referred to as a "solid." While
"solid" can describe the physical properties of wood (since wood is a
solid material), it's not typically used to describe a finished piece of
furniture like a table. In common usage, a "solid" usually refers to
the state of matter (as opposed to liquid or gas), or sometimes to the
structure (like solid wood), but not generally to a completed object like a
table.
Would you like to explore why
this term might be used or see alternative ways of describing the table?
d)
We can easily move our hand in the air, but to do the same
through a solid block of wood, we need a karate expert.
This statement highlights the
difference between moving through air and a solid object like wood. Air is a
fluid medium, meaning it allows easier movement due to lower resistance. On the
other hand, wood is a solid, and moving through it requires a significant
amount of force and skill, as it resists movement. A karate expert, trained in
precise and powerful techniques, can focus enough force in a small area to
break through the resistance of the wood. The difference lies in the physical
properties of the two substances: air offers little resistance, while wood is
dense and solid, requiring much more effort to penetrate.
5.
Liquids generally have a lower density than
solids. But you must have observed that ice floats on water. Find out why.
Ice floats on water because it
is less dense than liquid water. The reason for this lies in the molecular
structure of ice. Water molecules in the liquid state are closer together,
allowing them to move past each other. However, when water freezes to form ice,
the molecules arrange themselves in a crystalline structure with more space
between them, creating a less dense substance. This increased distance between
molecules in the solid form makes ice less dense than liquid water, allowing it
to float.
Exercise – 1.4 Page: 9
1. Convert the
following temperature to Celsius scale:
a. 300K
b. 573K
To convert Kelvin (K) to Celsius (°C), use the formula:
°C=K−273.15°C = K - 273.15
Now, let's apply this formula:
a. 300 K
°C=300−273.15=26.85°C°C = 300 - 273.15 = 26.85°C
b. 573 K
°C=573−273.15=299.85°C°C = 573 - 273.15 = 299.85°C
So:
·
a. 300 K = 26.85°C
·
b. 573 K = 299.85°C
·
2. What is the physical state of water at:
·
a. 250°C b.
100°C ?
·
At the following temperatures:
·
a. 250°C:
Water is in a gaseous state (steam), as this temperature is
well above water's boiling point (100°C at standard atmospheric pressure).
·
b. 100°C:
Water is at its boiling point and can exist as both liquid
and gas (steam). However, if it's under normal atmospheric
pressure, it is at the transition point between liquid and gas, boiling to form
steam.
3. For any substance, why does the temperature remain
constant during the change of state?
The temperature remains constant during a change of state
because the energy being supplied to the substance is used to break or form the
intermolecular bonds rather than increasing the kinetic energy of the particles
(which would raise the temperature). This energy is called latent heat. For
example, when ice melts to water or water boils to steam, the heat added goes
into overcoming the forces holding the molecules together, not into raising the
temperature.
4. Suggest a method to liquify atmospheric gases.
To liquefy atmospheric gases, you typically need to cool
them down and/or compress them to reach their liquefaction points. Here's a
common method to achieve this:
Cryogenic
Distillation Method:
1.
Compression: First, compress the atmospheric gases (mainly nitrogen, oxygen,
argon, and trace gases) using a compressor. Compression increases the pressure
of the gases, which causes them to heat up.
2.
Cooling: After compression, the gases are cooled using a heat exchanger.
This step allows the gas to lose the heat that was added during compression,
making the gas cooler.
3.
Expansion: The cooled, compressed gas is then passed through an expansion
valve, where it undergoes a rapid expansion. This expansion causes the gas to
cool further.
4.
Liquefaction: The temperature and pressure conditions eventually drop to the
point where the gases condense into liquid forms. This happens when each gas in
the mixture reaches its specific boiling point.
5.
Separation: Since the various gases in the atmosphere have different boiling
points, they can be separated by selectively adjusting the temperature and
pressure conditions. For example, nitrogen liquefies at a lower temperature
(-196°C), while oxygen liquefies at a slightly higher temperature (-183°C).
This method is used to separate liquid nitrogen, oxygen, and other gases.
Liquefaction
of Specific Gases:
·
Nitrogen (N₂): -196°C
·
Oxygen (O₂): -183°C
·
Argon (Ar): -185.7°C
This process is used in industries like air separation
plants, liquefied natural gas (LNG) production, and cryogenics.
Exercise – 1.5 Page:10
1. Why does a desert cooler cool better on a hot dry day?
A desert cooler, also known as an evaporative cooler, works
by cooling the air through the evaporation of water. It cools better on hot,
dry days because the process of evaporation is more efficient when the air is
dry.
When the air is dry, it can absorb more water vapor, so the evaporation process happens more quickly and efficiently, lowering the temperature of the air that is blown into the space. On humid days, the air already contains more moisture, so the evaporation process slows down, making the cooler less effective. That's why desert coolers are most effective in hot, dry climates where the air has a lower humidity level.
2. How does the water kept in an earthen pot (matka) become cool during summer?
Water in an earthen pot (matka) becomes cool during the
summer due to the process of evaporation. Earthen pots are porous, meaning they
have tiny holes that allow moisture to seep out. When the water inside the pot
comes into contact with the outer surface, some of it evaporates.
Evaporation is a cooling process because when water
molecules escape from the surface, they carry heat energy with them, which
reduces the temperature of the remaining water. Additionally, the porous nature
of the clay allows air to circulate, further enhancing this evaporative cooling
effect. This natural cooling mechanism helps to keep the water inside the pot
cool even on hot days.
3.Why
does our palm feel cold when we put on some acetone or petrol, or perfume on
it?
When we put acetone, petrol, or perfume on our palm, it
feels cold because of evaporative cooling. These substances
are volatile, meaning they evaporate quickly at room temperature. As they
evaporate, they absorb heat from our skin, causing a cooling sensation.
Here's how it works:
1.
Fast Evaporation: Acetone, petrol, and perfumes contain volatile compounds that
evaporate quickly.
2.
Heat Absorption: During evaporation, these liquids absorb heat energy from the skin
to convert from liquid to gas.
3.
Cooling Effect: As heat leaves the skin, the temperature of the skin drops, making
it feel cold.
This is the same principle that makes sweat cool our body
when it evaporates.
4.
Why are we able to sip hot tea or milk faster
from a saucer rather than a cup?
We can sip hot tea or milk
faster from a saucer rather than a cup because of increased surface
area. When the liquid is poured into a saucer, it spreads out,
exposing more of it to the air. This allows heat to escape more quickly through
evaporation and conduction, cooling the liquid faster than it would in a cup,
where it remains in a deeper, more concentrated form.
5.
What type of clothes should we wear in summer?
In summer, it’s best to wear light, breathable, and
comfortable clothing to stay cool and protect yourself from the sun. Here are
some ideal choices:
·
Fabric: Choose cotton, linen, or other lightweight, breathable fabrics to
allow airflow and absorb sweat.
·
Colors: Wear light-colored clothes (white, pastels, or beige) as they
reflect heat rather than absorb it.
·
Fit: Loose-fitting clothing allows better ventilation and keeps you
cooler.
·
Style: Opt for shorts, skirts, dresses, t-shirts, tank tops, and airy
shirts.
·
Accessories: Use hats, sunglasses, and light scarves for sun protection.
Chapter Exercise – Page: 12
1. Convert the
following temperature to Celsius scale.
(a) 293K
(b)
470K
To convert a temperature from Kelvin (K) to Celsius (°C),
use the formula:
°C=K−273.15°C = K - 273.15
(a) 293K to Celsius
293−273.15=19.85°C293 - 273.15 = 19.85°C
≈ 19.9°C
(b) 470K to Celsius
470−273.15=196.85°C470 - 273.15 = 196.85°C
≈ 196.9°C
2.Convert the
following temperatures to the Kelvin scale.
(a) 25°C (b)
373°C
To convert Celsius to Kelvin, use the formula:
K=°C+273.15K = °C + 273.15
(a) 25°C+273.15=298.15K25°C + 273.15 =
298.15K
(b) 373°C+273.15=646.15K373°C + 273.15 =
646.15K
So, the answers are:
(a) 298.15 K
(b) 646.15 K
3.
Give reason for the following observations:
(a)
Naphthalene balls disappear with time without leaving any solid.
Naphthalene balls disappear over time due to sublimation.
Sublimation is the process in which a solid changes directly into a gas without
passing through the liquid state. Naphthalene, being a volatile organic
compound, gradually transforms into vapor at room temperature, dispersing into
the air without leaving any solid residue.
(b)
We can get the smell of perfume while sitting several metres away.
Yes, we can smell perfume while sitting several meters away
due to the process of diffusion. Diffusion is the movement of
molecules from an area of higher concentration (near the perfume bottle) to an
area of lower concentration (surrounding air).
When perfume is sprayed, its fragrance particles mix with
air molecules and spread out. These particles move randomly and gradually reach
our nose, allowing us to perceive the scent even from a distance. This
phenomenon demonstrates how gases diffuse in the air.
4.Arrange
the following in increasing order of forces of attraction between the particles
– water, sugar, oxygen.
The forces of attraction between particles vary depending
on the state of matter:
·
Oxygen is a gas and has the weakest intermolecular forces.
·
Water is a liquid and has stronger intermolecular forces than gases but
weaker than solids.
·
Sugar is a solid and has the strongest intermolecular forces among the
three.
Thus, the increasing order of forces of attraction is:
Oxygen < Water < Sugar.
5. What is the
physical state of water at –
(a) 25°C (b) 0°C (c) 100°C?
The physical state of water at different temperatures is as
follows:
(a) 25°C – Liquid
(b) 0°C – Solid (ice) and liquid (water) coexist at this
temperature, as it is the freezing/melting point.
(c) 100°C – Liquid and gas (water vapor) coexist, as it is the
boiling point of water.
6.
Give two reasons to justify –
(a)
Water at room temperature is a liquid.
Yes, water at room temperature (approximately 25°C or 77°F)
is in the liquid state. This is because its melting point is 0°C (32°F) and its
boiling point is 100°C (212°F) under standard atmospheric pressure (1 atm). At
room temperature, water molecules have enough kinetic energy to remain in the
liquid phase but not enough to transition into a gas.
(b)
An iron almirah is a solid at room temperature.
Yes, an iron almirah is a solid at room temperature. Iron,
like most metals, has a solid state at typical room temperatures (around
20-25°C or 68-77°F). Iron melts at a much higher temperature, around 1,538°C
(2,800°F), so it remains solid under normal conditions.
7.Why is ice at 273K more effective in cooling than water at
the same temperature?
Ice at 273 K is more effective
in cooling than water at the same temperature because of its latent
heat of fusion. When ice melts at 273 K, it absorbs a significant
amount of heat (the latent heat of fusion) from the surroundings without
raising its temperature. This process allows it to absorb more heat than water
at the same temperature, thus cooling the surroundings more effectively.
In simpler terms, when ice
melts, it requires energy to break the bonds between the molecules, and this
energy comes from the surrounding environment, lowering the temperature of that
environment. Water, on the other hand, doesn't absorb as much heat at the same
temperature because it's already in a liquid state, and additional energy would
be required to raise its temperature.
8.
What produces more severe burns, boiling water
or steam?
Steam produces more severe burns
than boiling water. This is because steam contains more energy. When steam
comes into contact with skin, it condenses back into water, releasing this
extra heat. In contrast, boiling water only transfers heat through direct
contact. The additional heat energy in steam makes it much more dangerous and
capable of causing more severe burns.
9.
Name A, B, C, D, E and F in the following
diagram showing a change in its state.
(A) Solid to Liquid → Melting (or) fusion
(or) liquefaction
(B) Liquid to Gas → Evaporation (or)
vaporization
(C) Gas to liquid → Condensation
(D) Liquid to Solid → Solidification
(E) Solid to Gas → Sublimation
(F) Gas to Solid → solidification
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