Class 9 > Unit # 07:Properties of Matter > States of Matter


States of Matter and Phase Changes - Talha's Physics Academy

Talha's Physics Academy

States of Matter & Phase Transitions

7.1 States of Matter

"There are three primary states of matter: solid, liquid, and gas. All material objects around us belong to one of these states, with water serving as the classic multi-state example."
  • Solid State: Fixed shape and fixed volume (e.g., ice cubes, snow, glaciers, and icebergs).
  • Liquid State: Fluid state with a definite volume but no fixed shape, adapting to its container (e.g., water in oceans, rivers, and underground deposits).
  • Gaseous State: No fixed shape and no fixed volume (e.g., steam and invisible water vapors forming small visible clouds in the air).

Properties Comparison of States of Matter

State Shape Volume Density Compressibility
Solid Fixed Fixed High Incompressible
Liquid Not fixed Fixed High Incompressible
Gas Not fixed Not fixed Low Compressible

Changes of State (Energy Transfer)

The addition or removal of thermal energy can induce transitions between states of matter:

  • Melting: Conversion from solid to liquid.
  • Boiling: Conversion from liquid to gas throughout the liquid volume at its boiling point.
  • Condensing: Conversion from gas to liquid.
  • Freezing: Conversion from liquid to solid.
  • Evaporation: Conversion from liquid to gas taking place at temperatures below the boiling point.
Key Distinction: Evaporation vs. Boiling

While both represent phase transitions from liquid to gas, evaporation is a surface phenomenon occurring spontaneously at any temperature below the boiling point, whereas boiling occurs at a specific, fixed temperature throughout the entire liquid mass under given pressure.

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