Boiling

Boiling is an endothermic phase transition where a liquid changes rapidly into gas throughout the bulk of the liquid at a fixed temperature called the boiling point ¹.

Bulk Mechanism & Bubble Formation

Unlike surface evaporation, boiling occurs throughout the liquid when vapor pressure equals atmospheric pressure ²:

Thermal energy enables particles throughout the liquid to break attractive intermolecular forces.
Bubbles of vapor form internally and rise to escape.

Temp ^            / Gas       |  ^   ^  (Vapor escapes)
     |           /            | ( o )   (Bubbles form
B.P. +==========+ (Boiling)   | (   )    throughout liquid)
     +---------> Heat Added   +---------+

Latent Heat & Heating Curve

Temperature stays strictly constant at the boiling plateau until all liquid turns to gas ²:

$\Delta E = m \cdot l_v$

Supplied energy provides the specific latent heat of vaporization ( $l_v$ ) to fully separate particles without temperature rise ( $\Delta T = 0$ ) ².

Boiling vs. Evaporation

Location: Boiling occurs throughout bulk liquid; evaporation is surface-only ².
Temperature: Boiling requires the fixed boiling point; evaporation occurs at any temperature below it.
Bubbles: Boiling forms bubbles internally; evaporation does not.

Purity Criterion

Pure substances boil sharply at a precise temperature. Non-volatile impurities elevate the boiling point over a range ¹.

Endothermic Change - Process absorbing thermal energy from surroundings.
Intermolecular Force - Attractive forces overcome during boiling.
Condensation - Reverse exothermic gas-to-liquid transition.
Evaporation - Surface vaporization below the boiling point.
Melting - Solid-to-liquid transition.
Pure Substance - Single chemical species boiling at fixed sharp temperatures.
State of Matter - Classical states of matter.
Chemistry - Core science area.

Cambridge IGCSE Chemistry (0620) - Purity and boiling behavior. ↩ ↩²
Cambridge IGCSE Physics (0625) - Latent heat of vaporization and boiling mechanism. ↩ ↩² ↩³ ↩⁴