Changes of
State
also known as
Phase
Changes
What are phase changes?
• Phase changes (changes of state) are the
processes of changing from one state of matter
to another. (Example: solid to liquid)
• Phase changes are physical changes, so the
identity of the matter does not change.
• Phase changes are processes, NOT the same
things as the states of matter!
• States of matter are solid, liquid, gas, and plasma.
These are physical properties of matter.
What causes a change of state?
• Changes of state occur by adding or removing
heat energy (kinetic) from matter.
• Changes of state caused by adding heat energy
to matter are classified as endothermic
processes. (Endo = enter, heat goes in.)
• Changes of state caused by removing heat
energy are classified as exothermic processes.
(Exo = exit, heat goes out.)
•
Kinetic Energy is related to the motion of
the particles. If energy is added, the
particles move faster.
•
Temperature- measure of the speed of a
substance’s particles, and is the measure of
the amount of thermal energy.
•
Heat- The transfer of thermal energy
There are 6 main
changes of state
(phase changes) that
you will need to know:
 MELTING
• Melting is an endothermic (absorbs energy)
process in which a solid changes to a liquid.
• Melting point- Temperature at which a
substance changes from a solid to a liquid
 FREEZING
• Freezing is an exothermic process in which a liquid
changes to a solid.
VAPORIZATION
• Vaporization is an endothermic process in
which a liquid is changed to a gas.
• This can happen in two ways:
• Boiling is vaporization that occurs
throughout the liquid. The temperature
at which this occurs is the boiling point.
• Evaporation is vaporization that occurs
at the surface of a liquid. This occurs at
temperatures below the boiling point.
CONDENSATION
• Condensation is an exothermic process in
which a gas is changed to a liquid.
 SUBLIMATION
• Sublimation is an endothermic process in
which a solid is changed to a gas without
first melting to a liquid.
 DEPOSITION
• Deposition is an exothermic process in
which a gas is changed into a solid,
skipping the liquid phase.
STATES OF MATTER
SOLID
Tightly packed, in
a regular pattern
Vibrate, but do not
move from place to
place
LIQUID
Close together
with no regular
arrangement.
Vibrate, move
about, and slide
past each other
GAS
Well separated
with no regular
arrangement.
Vibrate and move
freely at high
speeds
PLASMA
Has no definite
volume or shape
and is composed of
electrical charged
particles
Temperature Change versus
Change of State
 When the temperature of a substance changes, the
speed of the particles also changes.
 When a substance is going through a change of state,
its temperature does not change until the change of
state is complete
 Temperature at which phase changes occur are unique
to the type of matter (characteristic property)
Heating Curve
A heating curve
• shows changes
of state as a
solid is heated.
• sloped lines
show increase
in temperature.
• plateaus (flat
lines) indicate a
change of state.
12
Cooling Curve
A cooling curve
• shows changes
of state as a gas
is cooled.
• sloped lines
indicate a
decrease in
temperature.
• plateaus (flat
lines) indicate
a change of
state.
13
Different matter, different temperatures
for phase changes
ABSOLUTE ZERO
• A temperature of 0 Kelvin is called
absolute zero.
• It is the temperature at which scientists
believe gas molecules have no kinetic
energy and all motion stops.
• On the Celsius scale, absolute zero is
equal to -273°C.
• Scientists have not yet achieved absolute
zero with matter.