Page 22 - Understanding NCERT Science 09

• The arrangement of particles is most ordered in the case of
solids, in the case of liquids layers of particles can slip and
slide over each other while for gases, there is no order,
particles just move about randomly.

• The states of matter are inter-convertible. The state of matter
can be changed by changing temperature or pressure.
• Sublimation is the change of solid state directly to gaseous
state without going through liquid state.

• Deposition is the change of gaseous state directly to solid
state without going through liquid state.
• Boiling is a bulk phenomenon. Particles from the bulk
(whole) of the liquid change into vapour state.
• Evaporation is a surface phenomenon. Particles from the
surface gain enough energy to overcome the forces of attraction
present in the liquid and change into the vapour state.

• The rate of evaporation depends upon the surface area exposed
to the atmosphere, the temperature, the humidity and the
wind speed.

• Evaporation causes cooling.

• Latent heat of vaporisation is the heat energy required to change
1 kg of a liquid to gas at atmospheric pressure at its
boiling point.

• Latent heat of fusion is the amount of heat energy required
to change 1 kg of solid into liquid at its melting point.
• Some measurable quantities and their units to remember:

Quantity Unit Symbol
Temperature kelvin K
Length metre m
Mass kilogram kg
Weight newton N
Volume cubic metre m 3
Density kilogram per cubic metre kg m –3
Pressure pascal Pa

MATTER IN OUR SURROUNDINGS 11

Rationalised 2023-24