Phase ChangesPhase ChangesChp 10

Phase Diagrams

• Phase diagram = relates physical states of matter (solid, liquid, gas) to temperature and pressure

Phase Diagrams

• Triple Point: the only set of conditions where all three physical states can exist in equilibrium

Phase Diagrams

• Critical Point = temperature at which a liquid turns to a gas and cannot be turned back into a liquid, no matter the pressure

TypicalPhase

Diagram

Phase Diagram

For Water

Phase Diagram:

• Sublimation = Moving from the solid to gaseous state with out passing through the liquid state

• Vaporization of a solid

Uses for sublimation:

• Freezing things like freshly brewed coffee, or food for campers and astronauts

• Dry ice- carbon dioxide in solid form- keeps things frozen during shipping

Uses for sublimation:

• Moth balls:

• Naphthalene sublimes into a vapor that keeps moths from damaging clothing and other things

Boiling and Freezing Graphs

Boiling & Freezing

• When a substance boils or freezes (or melts or condenses) the temperature of the system will remain constant (does not change) until the phase change is complete

Boiling• This means, boiling

water has a temp of 100oC, not higher.

• The temp will begin to rise when all the water is boiled away into steam

Freezing / Melting• This also means melting ice has a

temp of 0oC, not lower, not higher.

• The temp will begin to rise when all the ice is melted

Vapor Pressure • A liquid will begin to boil when its

vapor pressure equals the external pressure

• Thus, as the pressure in the room changes, the boiling point of the liquid will change as well.

Vapor Pressure • At standard pressure (1 atm) the

temperature at which a liquid will boil is called the normal boiling point

• You can use a vapor pressure graph to determine the boiling point of a liquid at any pressure

Vapor Pressure GraphAt standard pressure (760mmHg), liquid A will boil around 72oC. Liquid B will boil around 115oC. At what temps will they boil at 400mmHg?

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