Transcript Liquid-Gas Phase Changes

PHASE CHANGES
http://www.youtube.com/v/8Oq2Xl7oiws?version=3&hl=en_
Phases Changes in Matter:
(Also examples of Physical Changes)
1.
2.
3.
4.
5.
Melting
Freezing
Vaporization
Condensation
Sublimation
Physical Change: a substance changes from one form to another, but it
remains the same kind of substance. No new matter is
formed.
Solid-Liquid Phase Changes
Melting: the change of a solid to a
liquid.
1. Occurs when a substance absorbs
heat energy.
2. The crystal structure of the particles
breaks down, allowing the particles to
flow freely around one another.
Melting-point: the temperature at which a
solid changes to a liquid. (Ice melts at 0°C)
Melting
Liquid-Solid Phase Changes
Freezing: the change of a liquid into a solid.
1. occurs when a substance loses heat energy.
Freezing-point: the temperature at which a substance
changes from a liquid to a solid.
1. The freezing point of a substance is equal to its
melting point. ( ice melts at 0°C and water
freezes at 0°C)
Alcohols: have freezing points much lower than 0°C.
1. Used in automobile antifreeze.
2. Even the coldest winter temperatures will not
cause the water in the radiator to freeze.
Freezing
Liquid-Gas Phase Changes
Vaporization: the change of a substance from a
liquid to a gas.
1. Particles in a liquid absorb enough
heat energy to escape from the
liquid phase.
Evaporation: if vaporization takes place at the
surface of the liquid.
Condensation: if a substance in the gas phase
loses heat energy, it changes into a
liquid.
Example: 1) a cold glass iced drink tends to
become wet on the outside. This is
because water vapor condenses.
2) Rain
Condensation
Liquid-Gas Phase Changes
C. Boiling: particles inside a liquid change to gas, and
then the particles travel to the surface of the
liquid and into the air.
D. Boiling-point: the temperature at which a liquid boils.
Water boils at 100°C.
1. Related to the pressure of the air above it.
a. the lower the air pressure ( the less the
“push” of the air pressing down), the more
easily the bubbles of gas can form within
the liquid and then escape.
Lowering the air pressure lowers the boiling point.
b. at high altitudes the air pressure is much
lower, so you would be able to boil water at
ordinary room temperature.
Solid-Gas Phase Changes
Sublimation: when a substance’s
surface particles escape
directly into the gas
phase. They do not
pass through the liquid
phase.
Example: Dry Ice
www.youtube.com/embed/ukhtimOxECk
Sublimation
Dry Ice
Deposition: Gas to Solid

When water vapor
in air loses so
much energy it
turns directly into a
solid.

Frost!
Energy in Phase Change
DEPOSITION
More About the Phase Changes
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Earth is known as the “water” planet.
1. ¾ of the Earth’s surface is water
2. 1% of the Earth’s atmosphere exists in 3 phases
a. Ice
b. Liquid water
c. Water vapor
A solid substance has less energy than the same
substance in the liquid phase.
A gas usually has more energy than the liquid phase of
the same substance.
Ice has less energy than liquid water.
Steam has more energy than ice or liquid water.
More About the Phase Changes
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Because energy content is responsible for the different phases
of matter, substances can be made to change phase by adding
or taking away energy.
*The easiest way to do this is to heat or cool the
substance.
Examples: 1) Liquid water is put into freezer to remove
heat and make ice.
2) On a stove you add heat to make liquid
water turn to steam.
Physical Change: a substance changes from one form to another, but
it remains the same kind of substance. No new
matter is formed.
Chemical Properties/Changes
Chemical Properties: The properties that
describe how a substance changes into other new
substances.
Example: The ability of a substance to burn.
1. Flammability: The ability to burn. (Hydrogen)
2. Supporting-Burning (Oxygen)
Chemical Changes: The changes that substances
undergo when they turn into other substances.
Example: The process of burning.
Chemical Properties/Changes
A Chemical Property describes a substance’s
ability to change into a different substance;
A Chemical Change is the process by which the
substance changes.
Chemical Reaction: (another name for a chemical change)
The process in which the physical and chemical
properties of the original substance change as a
new substance with different physical and
chemical properties is formed.