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Volatile

Property of a substance that evaporates readily at normal temperatures due to weak intermolecular attractions.

#volatile#evaporation#intermolecular-forces#liquids#igcse-chemistry#igcse-physics

Volatile

In IGCSE Chemistry, a substance (typically a liquid) is described as volatile if it evaporates easily and rapidly at standard room temperature and pressure 1.

Kinetic Particle Mechanism

Whether a liquid is volatile depends on the strength of its intermolecular forces 1:

  • Weak Intermolecular Forces: Volatile liquids have weak forces attracting neighboring molecules together.
  • Rapid Surface Escape: Because attractive forces are weak, a large fraction of surface particles possess enough kinetic energy to break free into the gas phase at room temperature 2.
  • Low Boiling Point: Less thermal energy is required to overcome intermolecular attractions, resulting in relatively low boiling points 2.
Volatile Liquid (e.g. Propanone)    Less Volatile Liquid (e.g. Water)
     ^   ^   ^   (Rapid Escape)                   ^   (Slow Escape)
   (o) (o) (o)   Gas Phase                      (o)   Gas Phase
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 (o) - - (o) - - (o)                  (o) === (o) === (o)
    Weak intermolecular                  Strong intermolecular
    forces (easily broken)               hydrogen bonds

Typical IGCSE Examples

CategoryExamplesBoiling PointEvaporation Rate
VolatilePropanone (acetone), ethanol, petrolLow (56 ∘C56\text{ }^\circ\text{C} to 78 ∘C78\text{ }^\circ\text{C})Very Rapid
Non-Volatile / Less VolatileWater, cooking oil, molten saltsHigh (≥100 ∘C\ge 100\text{ }^\circ\text{C})Slow to negligible

Volatile liquids produce high vapor concentrations above the surface and are often flammable, requiring tightly stoppered containers and water baths rather than open Bunsen flames during heating 1.

  • Volatility - Measure of the tendency to vaporize.
  • Evaporation - Surface liquid-to-gas phase transition below boiling point.
  • Boiling - Bulk phase transition occurring at a fixed boiling point.
  • State of Matter - Macroscopic physical forms of matter.
  • Chemistry - Core science area.

Footnotes

  1. Cambridge IGCSE Chemistry (0620) - States of matter, volatility, and laboratory safety. ↩ ↩2 ↩3

  2. Cambridge IGCSE Physics (0625) - Kinetic particle model and evaporation. ↩ ↩2