Comprehensive Notes on Matter in Our Surroundings

Matter in Our Surroundings

Introduction

Everything in the universe is made up of "matter."
Matter occupies space and has mass, thus possessing both mass and volume.
Early Indian philosophers classified matter into five basic elements: air, earth, fire, sky, and water (the "Panch Tatva").
Ancient Greek philosophers had similar classifications.
Modern scientists classify matter based on physical properties and chemical nature.
This chapter focuses on the physical properties of matter; chemical aspects will be covered later.

1.1 Physical Nature of Matter

1.1.1 Matter is Made Up of Particles

Two prevailing schools of thought:
- Matter is continuous (like a block of wood).
- Matter is made up of particles (like sand).
Activity 1.1 demonstrates the particulate nature of matter:
- Dissolving salt or sugar in water shows that the salt/sugar spreads throughout the water.
- This indicates that matter is composed of particles.

1.1.2 How Small Are These Particles of Matter?

Activity 1.2 illustrates the small size of particles:
- Dissolving 2-3 crystals of potassium permanganate in 100 mL of water, then diluting this solution repeatedly, shows that the color is still visible even after several dilutions.
- This demonstrates that a single crystal of potassium permanganate contains millions of tiny particles that keep dividing into smaller particles.
- The same activity can be performed with 2 mL of Dettol.
- Conclusion: Particles of matter are very small, beyond our imagination.

1.2 Characteristics of Particles of Matter

1.2.1 Particles of Matter Have Space Between Them

Activities 1.1 and 1.2 show that particles of sugar, salt, Dettol, or potassium permanganate get evenly distributed in water.
When making tea, coffee, or lemonade, particles of one type of matter fit into the spaces between particles of the other.
This indicates sufficient space between particles of matter.

1.2.2 Particles of Matter Are Continuously Moving

Particles of matter possess kinetic energy and are continuously moving.
As temperature increases, particles move faster, increasing their kinetic energy.
Activity 1.3: Observing the smell of an unlit vs. lit incense stick demonstrates particle movement.
Activity 1.4: Observing the diffusion of ink and honey in water shows the movement of particles.
Activity 1.5: Observing the mixing of copper sulfate or potassium permanganate in hot vs. cold water demonstrates that the rate of mixing (diffusion) changes with temperature.
Intermixing of particles of two different types of matter on their own is called diffusion.
Diffusion becomes faster with heating.

1.2.3 Particles of Matter Attract Each Other

Particles of matter have forces acting between them, keeping them together.
The strength of this force varies from one kind of matter to another.
Activity 1.6: Forming human chains and trying to break them illustrates the force of attraction between particles.
Activity 1.7: Trying to break an iron nail, chalk, and rubber band demonstrates varying forces of attraction.
Activity 1.8: Trying to cut the surface of water with fingers shows the force keeping water molecules together.

1.3 States of Matter

Matter exists in three states: solid, liquid, and gas.
These states arise due to variations in the characteristics of the particles of matter.

1.3.1 The Solid State

Activity 1.9: Collecting articles like a pen, book, needle, and wooden stick to observe their shape, boundaries, and volume.
Solids have a definite shape, distinct boundaries, and fixed volume.
They have negligible compressibility and maintain their shape when subjected to outside force (they are rigid).
Exceptions:
- A rubber band changes shape under force but regains it when the force is removed (it's a solid).
- Sugar and salt crystals have a fixed shape whether in hand, plate, or jar (they are solid).
- A sponge has minute holes filled with air, allowing compression (it's a solid).

1.3.2 The Liquid State

Activity 1.10: Collecting liquids like water, cooking oil, milk, juice, and cold drinks to observe their shape and volume in different containers.
Liquids have no fixed shape but have a fixed volume.
They take the shape of the container in which they are kept.
Liquids flow and change shape, so they are not rigid but are considered fluid.
Solids, liquids, and gases can diffuse into liquids.
Gases from the atmosphere (especially oxygen and carbon dioxide) diffuse and dissolve in water, essential for aquatic life.
The rate of diffusion of liquids is higher than that of solids due to greater space between particles and free movement.

1.3.3 The Gaseous State

Gases are highly compressible compared to solids and liquids.
Liquefied petroleum gas (LPG) and compressed natural gas (CNG) are examples of compressed gases.
Activity 1.11: Compressing water, chalk and air in syringes to demonstrate compressibility.
Gases diffuse very fast due to high particle speed and large spaces between them.
Particles in the gaseous state move randomly at high speed, hitting each other and the walls of the container.
The pressure exerted by a gas is due to the force exerted by gas particles per unit area on the walls of the container.

1.4 Can Matter Change its State?

Water can exist in three states: solid (ice), liquid (water), and gas (water vapor).

1.4.1 Effect of Change of Temperature

Activity 1.12: Heating ice in a beaker to observe the conversion from solid to liquid and then to gas.
Increasing the temperature of solids increases the kinetic energy of the particles, causing them to vibrate faster.
At the melting point, the solid converts to a liquid.
The melting point is an indication of the strength of the forces of attraction between particles.
The melting point of ice is $273.15 K$ .
Melting is also known as fusion.
Latent heat: During melting, the temperature remains constant as the heat energy is used to overcome the forces of attraction between particles.
The amount of heat energy required to change 1 kg of a solid into a liquid at atmospheric pressure at its melting point is the latent heat of fusion.
Particles in water at $0^\circ C$ ( $273 K$ ) have more energy than particles in ice at the same temperature.
At the boiling point, a liquid starts changing into gas.
The temperature at which a liquid starts boiling at atmospheric pressure is known as its boiling point.
For water, this temperature is $373 K$ ( $100^\circ C$ ).
Particles in steam at $373 K$ ( $100^\circ C$ ) have more energy than water at the same temperature due to latent heat of vaporization.
Kelvin is the SI unit of temperature; $0^\circ C = 273.15 K$ , often rounded to $273 K$ for convenience.
To convert from Kelvin to Celsius, subtract 273; to convert from Celsius to Kelvin, add 273.
Substances can change directly from solid to gaseous state (and vice versa) without changing into the liquid state.
Activity 1.13: Observing the sublimation of camphor.
Sublimation: The change of state directly from solid to gas.
Deposition: The direct change of gas to solid.

1.4.2 Effect of Change of Pressure

The difference in states of matter is due to the distances between particles.
Applying pressure and reducing temperature can liquefy gases.
Solid carbon dioxide ( $CO_2$ ) is stored under high pressure and converts directly into a gaseous state on decrease of pressure to 1 atmosphere (dry ice).
Pressure and temperature determine the state of a substance.

1.5 Evaporation

Evaporation: The phenomenon of change of liquid into vapors at any temperature below its boiling point.

1.5.1 Factors Affecting Evaporation

Activity 1.14: Observing the evaporation rate of water under different conditions (test tube vs. open dish, near window/fan vs. in cupboard).
The rate of evaporation increases with:
- An increase of surface area: Evaporation is a surface phenomenon.
- An increase of temperature: More particles gain enough kinetic energy to enter the vapor state.
- A decrease in humidity: High humidity decreases the rate of evaporation.
- An increase in wind speed: Wind carries away water vapor, decreasing the amount in the surrounding air.

1.5.2 How Does Evaporation Cause Cooling?

Liquid particles absorb energy from the surroundings to regain energy lost during evaporation, making the surroundings cold.

Key Concepts

Matter: Anything that occupies space and has mass.
Diffusion: Intermixing of particles of two different types of matter on their own.
Kinetic Energy: Energy possessed by particles due to their motion; increases with temperature.
Melting Point: The temperature at which a solid melts to become a liquid at atmospheric pressure.
Boiling Point: The temperature at which a liquid starts boiling at atmospheric pressure.
Latent Heat of Fusion: The heat energy required to change 1 kg of a solid into a liquid at its melting point.
Latent Heat of Vaporization: The heat energy required to change 1 kg of a liquid to gas at its boiling point.
Sublimation: The change of a solid directly into a gas.
Deposition: The change of a gas directly into a solid.
Evaporation: The change of a liquid into vapors below its boiling point.
Humidity: The amount of water vapor present in the air.

Numerical Relationships and Units

Density = Mass / Volume
$0^\circ C = 273.15 K$ (or approximately $273 K$ )
$K = ^\circ C + 273$
$^\circ C = K - 273$
1 atmosphere = $1.01 \times 10^5 Pa$

Units of Measurement

Temperature: Kelvin (K)
Length: Meter (m)
Mass: Kilogram (kg)
Weight: Newton (N)
Volume: Cubic meter ( $m^3$ )
Density: Kilogram per cubic meter ( $kg/m^3$ )
Pressure: Pascal (Pa)