Phase Phase ChangeChange

When a substance changes from one When a substance changes from one state, or phase, of matter to another we state, or phase, of matter to another we say that it has undergone a change of say that it has undergone a change of

state, or we say that it has undergone a state, or we say that it has undergone a change of phase.change of phase.

Phase Diagram

The different phases of a system may be represented using a phase diagram. The axes of the diagrams are the relevant thermodynamic variables. For simple mechanical systems, we generally use the pressure and temperature. The following figure shows a phase diagram for a typical material exhibiting solid, liquid and gaseous phases.

Description of Phase Change

Term for Phase Change

Heat Movement During Phase Change

Temperature Change During Phase

Change

Solid to liquid MeltingHeat goes into the

solid as it melts.None

Liquid to solid FreezingHeat leaves the

liquid as it freezes.

None

Liquid to gasVaporization, which

includes boiling and evaporation

Heat goes into the liquid as it vaporizes.

None

Gas to liquid CondensationHeat leaves the gas

as it condenses.None

Solid to gas SublimationHeat goes into the

solid as it sublimates.

None

EvaporationEvaporation

•the conversion of water from a liquid into a gas

What isWhat is

CONDENSATION?CONDENSATION?

• Condensation is the formation of Condensation is the formation of liquid drops from water vapor. liquid drops from water vapor.

• Condensation usually occurs Condensation usually occurs when a parcel of rising air when a parcel of rising air expands and cools. expands and cools.

• If it cools enough, some of the If it cools enough, some of the water vapor molecules clump water vapor molecules clump together faster than they are torn together faster than they are torn apart from their thermal energy. apart from their thermal energy.

• A very important part of this A very important part of this process is the release of the process is the release of the latent heat of condensation. latent heat of condensation.

Equilibrium is reached in a closed system whenthe rate of evaporation equals the rate of condensation

DepositionDeposition

• in sub-freezing air, in sub-freezing air, water vapor changes water vapor changes directly to ice without directly to ice without first becoming a first becoming a liquid. This is how liquid. This is how snow forms in clouds, snow forms in clouds, as well as frost and as well as frost and hoar frost on the hoar frost on the ground. The reverse ground. The reverse of deposition is of deposition is sublimationsublimation

FreezingFreezing

Transformation of liquid to solidTransformation of liquid to solid

Sublimation of Dry Ice and IodineThey change from solid <---> gas

Skipping the liquid state.

MeltingMeltingThe melting point of a solid is the temperature at which it changes state from solid to liquid