Class 9 Matter In Our Surroundings Notes

Notes Important Questions NCERT Solutions MCQ Quiz – 1 MCQ Quiz – 2

Matter In Our Surroundings Notes

Physical Nature of Matter:-

• Matter is made up of particles.
• Particles of matter are very small that we can’t see by our naked eyes.

Characteristics of Particles of Matter:-

• Particles of matter have space between them.
• Particles of matter are continuously moving.
• Particles of matter attract each other.

We can change the state of matter :-

• by changing the temperature.
• by changing the pressure.

Diffusion:-

The intermixing of particles of two different types of matter on their own is called diffusion.

• On increasing the temperature, the kinetic energy of the particles increases and the particles move faster and so diffusion becomes faster.

Boiling Point:- The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.

Melting Point:- The temperature at which a solid starts melting to become a liquid at the atmospheric pressure is known as its melting point.

• Melting point of ice = 0 ^oC = 273.16 K
• Boiling point of water = 100 ^oC = 373.16 K

Interconversion of three States of Matter:-

Fusion:- The process of change of solid into liquid state is known as fusion.

Sublimation:- The conversion of solid directly into gaseous state without changing into liquid state (or vice versa) is called sublimation.

• Some sublimable solids are ammonium chloride, camphor, dry ice (solid form of CO₂) etc.

Vaporisation:- The conversion of a liquid into gaseous state at its boiling point is called vaporisation.

Latent heat of Fusion:-

The amount of heat energy required to change 1 kg of solid into liquid at atmospheric pressure at its melting point is known as latent heat of fusion.

Latent heat of vaporisation:-

The amount of heat energy required to change 1 kg of liquid into gaseous state at the atmospheric pressure at its boiling point is known as latent heat of vaporisation.

Evaporation:-

The conversion of a liquid into gaseous state at any temperature below its boiling point is called evaporation.

Factors on which rate of evaporation depends are:-

• Surface Area:- On increasing surface area, rate of evaporation also increases.
• Temperature:- On increasing the temperature, rate of evaporation also increases.
• Wind Speed:- With the increase in wind speed, rate of evaporation also increases.
• Humidity:- With the increase in humidity, rate of evaporation decreases.

• During evaporation, the liquid absorbs heat energy from the surroundings to get converted into gaseous state and so, evaporation causes cooling.

Differences Between Vaporisation and Evaporation:-

S. No.	Evaporation	Vaporisation (Boiling)
1.	The conversion of a liquid into gaseous state at any temperature below its boiling point is called evaporation.	The conversion of a liquid into gaseous state at its boiling point is called vaporisation.
2.	It is a surface phenomenon.	It is a bulk phenomenon.
3.	It is a slow process.	It is a fast process.
4.	It causes cooling.	It does not cause cooling.

• Now scientists are talking of five states of matter: Solid, Liquid, Gas, Plasma and Bose-Einstein Condensate.

Formulas for interconversion of different units of temperature:-

• ^oF = (9/5) ^oC + 32
• ^oC = (5/9) (^oF -32)
• K = ^oC + 273.16
• ^oC = K -273.16

• S.I. unit of temperature is Kelvin (K)