Matter in Our Surroundings

1. Introduction to Matter

Definition: Matter is anything that occupies space (volume) and has mass.
Examples: Air, food, stones, clouds, stars, plants, animals, and water droplets.
Ancient Classification (Panch Tatva): Early Indian philosophers classified matter into five basic elements: Air, Earth, Fire, Sky, and Water.
Modern Classification: Scientists classify matter based on physical properties and chemical nature. This chapter focuses on physical properties.

Particulate Nature: Matter is not continuous (like a block of wood) but is made up of particles (like sand).
Extremely Small Size: Particles are small beyond imagination. For example, a few crystals of potassium permanganate or a few milliliters of Dettol can colour or scent a large volume of water (1000 L), showing that one crystal contains millions of tiny particles.

Particles have space between them.
Evidence: When dissolving salt, sugar, or potassium permanganate in water, the particles of the solute get into the spaces between the particles of water.

Particles are continuously moving and possess Kinetic Energy.
Temperature Effect: As temperature rises, particles move faster because their kinetic energy increases.
Diffusion: The intermixing of particles of two different types of matter on their own is called diffusion. Heating accelerates diffusion.

Particles attract each other; this force keeps them together.
The strength of this force varies: it is strongest in solids (e.g., iron nail), intermediate in liquids (e.g., water), and weakest in gases (e.g., air).

Definite shape, distinct boundaries, and fixed volume.
Rigid: Maintains shape when subjected to outside force.
Negligible compressibility.
Note: Sponges are solids but compressible because air is trapped in minute holes. Rubber bands change shape under force but regain it when the force is removed.

No fixed shape but has a fixed volume. Takes the shape of the container.
Fluid: Flows and changes shape; not rigid.
Liquids have more space between particles than solids and allow diffusion of solids, liquids, and gases (e.g., aquatic animals breathe dissolved oxygen).

No fixed shape or volume.
Highly Compressible: Large volumes can be compressed into small cylinders (e.g., LPG, CNG, Oxygen cylinders).
Particles move randomly at high speed, exerting pressure on container walls.
Very fast rate of diffusion.

Solid to Liquid (Melting): Heat overcomes attraction forces.
- Melting Point: Temperature at which solid melts to liquid at atmospheric pressure. Indicates strength of particle attraction.
- Latent Heat of Fusion: Heat energy required to change 1 kg of solid to liquid at melting point. Temp remains constant during melting as heat is used to change state.
Liquid to Gas (Boiling): Particles gain enough energy to break free.
- Boiling Point: Temperature at which liquid starts boiling. It is a bulk phenomenon.
- Latent Heat of Vaporisation: Heat energy required to change 1 kg of liquid to gas at atmospheric pressure at boiling point.
Sublimation: Direct change from solid to gas without becoming liquid (e.g., Camphor, Ammonium chloride).
Deposition: Direct change from gas to solid.

Temperature Unit Conversion:
SI unit is Kelvin (K).
0°C = 273 K (approx).
Kelvin = Celsius + 273.
Celsius = Kelvin - 273.

Applying pressure and lowering temperature can liquefy gases.
Dry Ice: Solid Carbon Dioxide (CO₂). Converts directly to gas when pressure is reduced to 1 atmosphere.

Definition: Change of liquid into vapour at any temperature below its boiling point.
It is a surface phenomenon.

Evaporation causes cooling because particles absorb energy from surroundings to regain lost energy.
Examples: Acetone on palm, water in earthen pot (matka), sprinkling water on hot roofs, wearing cotton in summer (absorbs sweat for evaporation).