Changes of State (Phase
Changes)
Textbook pp. 74-79
A change of state is the
conversion of a substance from
one physical form to another. All
changes of state are
physical changes.
Changes Of State

1.
2.
3.
4.
5.
There are five changes of state. They are:
Melting
Freezing
Vaporization
Condensation
Sublimation
During a change of state, the
energy of a substance changes.
If energy is added to a substance,
its particles move faster.
If energy is removed from a
substance, its particles move
slower.
TEMPERATURE
The temperature of a substance is a
measure of the speed of its particles
and is therefore a measure of its
energy.
 As substances heat up, the particles
move faster
 As particles cool down the particles
move slower

MELTING




The change of state from a solid to a liquid.
The melting point of a substance is the
temperature at which it changes from a solid
to a liquid
Melting is an endothermic change because
energy is absorbed by the substance as it
changes state.
Melting point and boiling point are
characteristic properties of a substance.
MELTING
FREEZING





The change of state from a liquid to a solid.
The freezing point of a substance is the temperature
at which a liquid changes into a solid.
Freezing is the opposite process of melting.
Freezing and melting occur at the same
temperature.
Freezing is an exothermic change because energy
is taken out of (exits) the substance as it changes.
FREEZING
VAPORIZATION

The change in state from a liquid to a gas.
2 KINDS OF VAPORIZATION


Boiling vaporization that
occurs throughout
a liquid.
The boiling point is
the temperature at
which a liquid boils.
2 KINDS OF VAPORIZATION


Evaporation – occurs
at the surface of a
liquid at a
temperature below its
boiling point.
Perspiration is the
cooling off of the body
through evaporation.
BOILING POINT




Pressure affects the boiling point of a
substance.
The boiling point of a substance
decreases as atmospheric pressure
decreases.
Water boils at a lower temperature on the
top of a mountain than it does at sea level.
Vacuum Sealer Demo.
CONDENSATION



The change of state from a gas to a liquid.
The condensation point of a substance is the
same thing as the boiling point.
Condensation is an exothermic change.
(energy exits)
SUBLIMATION



Change of state directly from a solid to a gas.
Dry ice sublimes; iodine sublimes; moth balls
sublime.
Sublimation is an endothermic change.
SUMMARIZING THE CHANGES OF
STATE
Change of State
Direction
Endothermic or
exothermic
Example
Melting
Solid to liquid
Endothermic
ice melts into
liquid water at 0°C
Freezing
Liquid to solid
Exothermic
Liquid water
freezes into ice at
0°C
Vaporization
Liquid to gas
Endothermic
Liquid water
vaporizes into
steam at 100°C
Condensation
Gas to liquid
Exothermic
Steam condenses
into liquid at
100°C
Sublimation
Solid to gas
Endothermic
Dry ice sublimes
into a gas
SUMMARIZING THE CHANGES OF
STATE OF WATER
TEMPERATURE CHANGES VS.
CHANGE OF STATE
 See
Figure 7 on page 79 of text
 Since temperature is a measure
of the speed of particles when the
temperature of a substance
changes, the speed of its particles
also changes.
TEMPERATURE CHANGES VS.
CHANGE OF STATE

When a substance changes state its
temperature does not change until the
change of state is complete.