Matter In Our Surroundings | Class 9 Science Notes Chapter 1

Matter In Our Surroundings | Class 9

• Matter refers to anything that has mass and occupies space. It includes substances like hydrogen, oxygen, sugar, sand, air, and water, which are made up of tiny particles with space between them.
• Matter can exist in three states: solid, liquid, and gas. The classification is based on interparticle forces and particle arrangement. Solids have a fixed shape and volume, liquids have no fixed shape but have volume, and gases have neither definite shape nor volume.
• The states of matter are interconvertible by changing pressure and temperature. For example, ice (solid) can be converted into water (liquid) by increasing the temperature.

Table: Properties of Solid, Liquid, and Gas

Property	Solid	Liquid	Gas
Shape and volume	Fixed shape and volume	No fixed shape but has volume	Neither definite shape nor volume
Energy	Lowest	Medium	Highest
Compressibility	Difficult	Nearly difficult	Easy
Arrangement of molecules	Regular and closely arranged	Random and little sparsely arranged	Random and more sparsely arranged
Fluidity	Cannot flow	Flows from higher to lower level	Flows in all directions
Movement	Negligible	Depends on interparticle attraction	Free, constant, and random
Interparticle space	Very less	More	Large
Interparticle attraction	Maximum	Medium	Minimum
Density	Maximum	Medium	Minimum
Rate of diffusion	Negligible	It depends on interparticle attraction.	Maximum

Physical Nature of Matter

• Physical properties of matter are observable or measurable characteristics that do not change the nature or composition of the substance.
• These properties are independent of the amount of matter present and include appearance, color, odor, density, texture, melting point, boiling point, solubility, etc.

Characteristics of Particles of Matter

1. Particles of matter have spaces between them:
   • The solubility of a substance in other substances is related to this characteristic.
   • When sugar dissolves in water, the sugar particles fill the interparticle spaces between the water particles without increasing the water level.
2. Particles of matter are always in motion:
   • The kinetic energy possessed by particles of matter causes them to exhibit continuous random movements.
   • Increasing the temperature increases the kinetic energy, making the particles move more vigorously.
3. Particles of matter attract each other:
   • Every substance has interparticle forces of attraction between its particles.
   • Breaking a substance requires overcoming this force, which varies in strength between different substances.

Diffusion

• Diffusion is the phenomenon of particles intermixing with each other spontaneously.
• During diffusion, particles occupy interparticle spaces and move from higher to lower concentration areas.
• The rate of diffusion increases with higher temperature due to increased particle kinetic energy.

Can Matter Change Its State?

• Changing the temperature of matter affects the kinetic energy of its particles.
• Increasing temperature increases the kinetic energy, weakening the interparticle forces and allowing particles to move freely.
• Solids can change to liquids, and liquids can change to gases when their respective interparticle forces are weakened.

Melting Point

• The melting point is the temperature at which a solid changes to a liquid at atmospheric pressure.
• At the melting point, both solid and liquid states coexist in equilibrium.

Boiling Point

• The boiling point is the temperature at which the vapor pressure of a liquid equals the atmospheric pressure.
• It represents the temperature at which a substance changes from the liquid phase to the gas phase.

Latent Heat of Fusion

• The latent heat of fusion is the amount of heat energy required to convert 1 kg of a solid into a liquid at its melting point and atmospheric pressure.

Latent Heat of  Vaporisation

• The latent heat of vaporization is the amount of heat energy required to convert 1 kg of a liquid into a gas at its boiling point and atmospheric pressure.

Sublimation

• Sublimation is the phase transition in which a substance directly changes from the solid phase to the gaseous phase (or vice versa) without passing through the liquid phase.

Effect of Change in Pressure on the State of Matter

• By applying pressure and reducing temperature, the interparticle spaces between particles of matter decrease.
• This allows for the conversion of a solid to a liquid and a liquid to a gas.

Evaporation

• Evaporation is the process by which molecules in the liquid state transition to the gaseous phase below the boiling point.
• Factors affecting evaporation include temperature, surface area, humidity, and wind speed.

Cooling Due to Evaporation

• During evaporation, particles of a liquid absorb energy from the surroundings to overcome interparticle forces and change phase.
• The absorption of heat causes a cooling effect in the surroundings.
• For example, sweating cools down our bodies.

Applications of Evaporative Cooling

• Earthenware containers are used to keep water cool. The porous surface of the pot allows for increased evaporation, thus cooling the water inside.
• Evaporation of sweat from our bodies helps cool us down.

• Wearing cotton clothing in the summer promotes evaporation, resulting in a cooling effect.

Read More: THE FUNDAMENTAL UNIT OF LIFE- CELL| Class 9

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