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Important Notes Important Notes for class 9 Chemistry Chapter :- 1 Kendriya Vidyalaya By Sarvagya
Key Concepts:
Classification of Matter
Early Indian philosophers
classified matter into five basic
elements, called the Panch- Tantva.
1. Air
2. Water
3. Earth
4. Sky
5. Fire
But nowadays, matter is
classified into groups according
to their physical properties and
chemical properties. Which are:-
1. On the basis of physical
properties:
a. Solid
b.Liquid
So Particles of solid have negligible movement between them. Solid have definite shape, distinct boundaries, and fixed volumes. So they have negligible compressibility. Solids can break under force but it is difficult to change their shape.
Important Question:
Q1. Why Sponge can be compress
even though it is solid?
A- Sponge can be compressed
because it has minute holes, in
which air is trapped. When it is
pressed, the air is expelled out
and we are able to compress it.
Liquid State :
Liquids take the shape of the container because their particles are loosely packed
and can move freely. So they have no fixed shape Unlike gases, liquids have a definite volume and do not expand to fill the entire container. So they have fixed volume. Particles in a liquid are loosely arranged with more space between them than in solids but less than in gases. So they have large intermolecular space than solid. Liquids are almost incompressible because their particles are already close together. Liquids can mix with each other due to diffusion (e.g., ink spreading in water). Gases: Gases completely fill any container they are placed in because their particles move freely in all directions. So they have no fixed shape and volume. Gases are highly compressable. Gases have large intermolecular spaces , making them less rigid and highly compressible.
Solid → Gas (Sublimation) : Some solids change directly into gas without becoming liquid (e.g., camphor, dry ice).
Scales of Measuring of Temperature:
Kelvin is the SI unit of temperature (k). Kelvin o = celcius o
- 273 Celcius o = Kelvin o
- 273 Latent Heat: Latent heat is the heat energy absorbed or released by a substance during a change of state , without changing its temperature. Latent heat of fusion: The heat required to change 1 kg of a solid into a liquid at its melting point without changing temperature. Example: Ice at 0°C absorbs heat and melts into water at 0°C. Latent Heat of Evaporation: The heat required to change 1 kg of a liquid into a gas at its boiling point without changing temperature.
Example: Water at 100°C absorbs heat and turns into steam at 100°C.
Evaporation:
The process by which a liquid changes into gas at a temperature below its boiling point.
Factors affecting Evaporation :
Temperature – Higher temperature = faster evaporation. Surface Area – Larger surface = faster evaporation (e.g., wet clothes dry faster when spread out). Humidity – More humidity = slower evaporation. Wind Speed – Higher wind speed = faster evaporation.
Evaporation causing cooling :
During evaporation, liquid particles absorb heat energy from their surroundings to gain enough energy to escape as gas. This heat is taken from the nearby surface, making it cooler.
