What is meant by bulk phenomena?

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Detailed Solution

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.

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