QUICK REVISION NOTES

Class 9 Science - Chapter 1: Matter in Our Surroundings

1. Introduction to Matter

• Matter: Anything that occupies space and has mass. (Example: Air, water, stone, table, etc.)
• Physical Nature of Matter:
  • Matter is made up of tiny particles (atoms or molecules).
  • These particles are extremely small.

2. Characteristics of Particles of Matter

• Space between particles: Particles of matter have spaces between them. (When we dissolve sugar in water, sugar particles occupy the spaces between water particles).
• Continuous motion: Particles of matter are constantly moving (possess kinetic energy).
  • Diffusion: Intermixing of particles of two different types of matter on their own. Increases with an increase in temperature.
• Attractive forces: Particles of matter attract each other with a force known as inter-particle force of attraction.

3. States of Matter

Matter exists mainly in three physical states:

4. Effect of Temperature and Pressure

• Melting Point (Fusion): The temperature at which a solid melts to become a liquid at atmospheric pressure.
  • Latent Heat of Fusion: The amount of heat energy required to change 1 kg of a solid into liquid at its melting point without any change in temperature.
• Boiling Point: The temperature at which a liquid starts boiling at atmospheric pressure.
  • Latent Heat of Vaporization: The amount of heat energy required to change 1 kg of liquid to gas at atmospheric pressure at its boiling point.
• Sublimation: The direct change of state from solid to gas without changing into liquid state (and vice-versa).
  • Examples: Camphor, Ammonium chloride, Naphthalene.

5. Temperature Conversion Formulas

To convert between Celsius (°C) and Kelvin (K):

• Celsius to Kelvin: Temperature in Kelvin (K) = °C + 273.15 (or simply + 273)
• Kelvin to Celsius: Temperature in Celsius (°C) = K - 273

6. Evaporation

• Definition: The phenomenon of a liquid changing into vapours at any temperature below its boiling point.
• Factors Affecting Evaporation:
  1. Surface Area: Increase in surface area increases evaporation.
  2. Temperature: Increase in temperature increases evaporation (rate of evaporation).
  3. Humidity: Decrease in humidity increases evaporation.
  4. Wind Speed: Increase in wind speed increases evaporation.
• Cooling Caused by Evaporation: The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation, causing a cooling effect (e.g., sweating, wearing cotton clothes in summer).

7. Plasma and Bose-Einstein Condensate (BEC)

• Plasma: Consists of super energetic and super excited particles in the form of ionized gases (e.g., Neon sign bulbs, Sun and stars glow due to plasma).
• Bose-Einstein Condensate (BEC): Formed by cooling a gas of extremely low density to super-low temperatures.