What is meant by bulk phenomena?

Physical phenomena can be classified into two types based on where molecular activity takes place: surface phenomena and bulk phenomena.

1. Surface Phenomena

• These involve only the surface molecules of a substance, while the interior molecules remain unaffected.
• Example:Evaporation – only molecules at the liquid surface escape into the vapor phase.

2. Bulk Phenomena

• These involve all the molecules of a substance, including those in the interior as well as at the surface.
• Example:Boiling – the entire liquid participates in the phase change process.

Boiling vs. Evaporation

• Boiling:
  • A bulk phenomenon where heat energy is transferred throughout the liquid, not just at the surface.
  • Occurs only at the boiling point, when all molecules gain sufficient energy to change into vapor.
  • Indicates the strength of intermolecular forces (higher force = higher boiling point).
• Evaporation:
  • A surface phenomenon that takes place at any temperature.
  • Only molecules at the surface escape into the vapor phase.
  • The rest of the system remains unaffected.