Phase changes and Heat Flow

What is a phase change?

A physical change where a substance transitions between solid, liquid, and gas phases.

Do phase changes involve temperature change?

No — temperature stays the same during a phase change.

Do phase changes involve heat transfer?

Yes — energy is either absorbed (endothermic) or released (exothermic).

Endothermic

The system absorbs heat from surroundings.

What is fusion (melting)

Solid to Liquid (endothermic)

What is vaporization (boiling)

Liquid to Gas (endothermic)

What is sublimation?

Solid to Gas (endothermic)

Exothermic

The system releases heat to surroundings.

What is crystallization? (freezing)

Liquid to Solid (exothermic)

What is condensation?

Gas to Liquid (exothermic)

What is deposition?

Gas to Solid (exothermic)

What is meant by “endothermic” in a phase change?

Heat is absorbed to break intermolecular forces and allow the change.

What is meant by “exothermic” in a phase change?

Heat is released as particles slow down and form stronger attractions.

Why is freezing exothermic process, even though it happens in a cold environment?

Because the system releases heat to its surroundings as it forms stronger bonds in the solid?