3.3 Phase Changes
Phase changes:
melting
Energy Changes
freezing
vaporization
condensation
sublimation
deposition
The temperature of a substance does NOT change during a phase
change.
Energy is either released or absorbed during a phase change.
Exothermic – Energy is released/given off to the surroundings
Endothermic – Energy is taken/absorbed from the surroundings
Melting and Freezing:
The arrangement of molecules in water become more orderly
as water freezes, and less orderly as ice melts.
Melting – energy (heat) is absorbed to melt ice, so it is
endothermic
Freezing – energy (heat) is released, so it is exothermic
Vaporization and Condensation:
Vaporization – energy (heat) is absorbed to vaporize, so it is
endothermic
Condensation – exothermic
Evaporation – takes place at the surface of a liquid and
occurs at temperatures below the boiling point.
Boiling – When the vapor pressure becomes equal to the
atmospheric pressure
Sublimation and Deposition:
Sublimation – endothermic
Deposition - exothermic