Revision Notes For Chapter 1 Matter In Our Surroundings

Here we are providing class 9 science notes for revision. Students should be very serious in Class 9 because it is a gateway to higher education. We hope that this NCERT Notes For Class 9 Science Chapter 1 will help the students to get good scores.

NCERT Science


Class 9th Science NCERT Notes

You can find CBSE NCERT Notes For Class 9 Science for other chapters here.


TOPIC-1 Matter
  •  Anything that occupies space and has mass is named matter.
  • The matter is not continuous but rather consists of a large number of particles.

Characteristics of particles:

(i) A large number of particles constitute matter.
(ii) Particles of a matter are very small in size.
(iii) Particles of a matter have spaces between them.
(iv) Particles of matter are continuously in motion.
(v) Particles of matter attract each other.
 
♦ Matter around us exists in three states solid, liquid, and gas.

Solid-state:

(i) All solids have a definite shape, distinct boundaries, and fixed volumes, that is, have negligible compressibility.
 
(ii) Solids have a tendency to maintain their shape when subjected to an outside force.
 
(iii) Solids are rigid.

♦ Liquid state:

(i) Liquids have no fixed shape but have a fixed volume. They take up the shape of the container within which they are kept.
 
(ii) Liquids flow and change shape, so they are not rigid but can be called fluid.
 
(iii) The rate of diffusion of liquids is higher than that of solids. This is because of the actual fact that in the liquid state, particles move freely and have greater space between one another as compared to particles in the solid-state.

♦ Gaseous state:

(i) Gases are highly compressible as compared to solids and liquids.
 
(ii) The liquefied petroleum gas (LPG) cylinder that we get in our home for cooking or the oxygen supplied to hospitals in cylinders is compressed gas.
 
(iii) In the gaseous state, the particles move around randomly at high speed. Due to this random movement, the particles hit
one another and also the walls of the container. The pressure of a gas is applied to the walls of the vessel by the irregular moving gas particles.


TOPIC-2  Change in State of Matter

♦ Water can exist in three states of matter–
 
(i) Solid, as ice,
(ii) Liquid, as water, and
(iii) Gas, as water vapor.
 
♦ The states of matter are inter-convertible. The state of matter are often changed by changing temperature or pressure.
 
♦ SI unit of temperature is Kelvin

   T (K) = T (°C) + 273
 
♦ The temperature at which solid melts to form a liquid at atmospheric pressure is called the melting point. The melting point of ice is 273.16 K (O°C)
 
♦ The melting point of a solid is an indication of the strength of the force of attraction between its particles.
 
♦ The temperature at which a liquid starts boiling at the atmospheric pressure is known as the boiling point. The boiling point of water is 373 K (100° C).
 
♦ The latent heat of vaporization is the heat energy required to change 1 kg of liquid into a gas at atmospheric pressure at its boiling point. Boiling is a bulk phenomenon.
 
♦ The latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.
 
Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present within the liquid and change into the vapor state.

Factors affecting evaporation

Evaporation takes place only at the surface of the liquid while boiling can take place in all parts of the liquid.
 
♦ Evaporation is a continuous or ongoing process. Evaporation causes cooling.
 
♦ The rate of evaporation is affected by the surface area exposed to the atmosphere, temperature, humidity, and wind speed.
 
♦ Since evaporation is a surface phenomenon, therefore, it increases with an increase in surface area.
 
♦ Evaporation increases with an increase in temperature.
 
♦ Evaporation decreases with an increase in humidity.
 
♦ Evaporation increases with the increase in wind speed.

The transition of a substance directly from its solid phase to gaseous phase without changing into the liquid phase (or vice versa) is called sublimation.


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