Download Phase Changes

Phase Changes
Drill
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Convert 15 degrees Fahrenheit to Celsius
Convert your answer to Kelvin
How many states of matter exist?
What are they?
Review: 3 Phases of Matter
• Solid
• Liquid
• Gas
But are there
only 3?
STATES OF MATTER
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•
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• Four States vs. Four Phases?
Solid
Liquid
Gas
Plasma Is there another state?
What is a Phase Change?
• Is a change from one state of matter
(solid, liquid, gas ) to another.
• Phase changes are physical changes because:
- It only affects physical appearance, not
chemical make-up.
- Reversible
What happens during a phase change?
• During a phase change,
heat energy is either
absorbed or released.
• Heat energy is released as
molecules slow down and
move closer together.
• Heat energy is absorbed
as molecules speed up
and expand.
Types of Phase Changes
• Types of Phase Changes
Melting
• Phase change from a
solid to a liquid
• Molecules speed up,
move farther apart, and
absorb heat energy
Freezing
• Phase Change from a
liquid to a solid
• Molecule slow down,
move closer together
and release heat
energy.
PHASE CHANGES
Description of
Phase Change
Solid to
liquid
Term for Phase
Change
Melting
Liquid to
Freezing
solid
Heat Movement During
Phase Change
Heat goes into
the solid as it
melts.
Heat leaves the
liquid as it
freezes.
PHASE CHANGES
Description of
Phase Change
Liquid to
gas
Term for Phase
Change
Vaporization,
which includes Heat goes into the
boiling and
liquid as it vaporizes.
evaporation
Gas to liquid Condensation
Solid to gas
Heat Movement During
Phase Change
Sublimation
Heat leaves the gas
as it condenses.
Heat goes into the
solid as it sublimates.
Phases of Matter
• Is ENERGY being ADDED or TAKEN
AWAY in this phase change:
ADDED
The added energy has caused the
chocolate particles to speed up. Before
they were vibrating in place, now they
are moving fast enough to slip past one
another.
Solid
Liquid
© 2013 S. Coates
Phases of Matter
• Is ENERGY being ADDED or TAKEN
AWAY in this phase change:
ADDED
The added energy has caused the water
particles to speed up. Before they were
moving fast enough to slip past one
another, now they have enough energy to
break away from one another and expand.
Liquid
Gas
© 2013 S. Coates
Phases of Matter
• Is ENERGY being ADDED or TAKEN
AWAY in this phase change:
Taken Away
Taking away energy from a puddle
slows the water molecules down so
that they no longer slide past one
another.
Liquid
© 2013 S. Coates
Solid
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
Vaporization (Boiling)
• Phase change from a
liquid to gas. It occurs at
the boiling point of
matter.
• Molecules speed up,
move farther apart, and
absorb heat energy.
Evaporation
• Phase change from a
liquid to a gas on the
surface of a liquid
(occurs at all
temperatures).
• Molecules speed up,
move farther apart, and
absorb heat energy.
Condensation
• Phase change from a
gas to a liquid.
• Molecule slow down,
move closer together
and release heat
energy.
Sublimation
• Phase change from a
solid to a gas.
• Molecules speed up,
move farther apart, and
absorb heat energy.
Deposition
• Phase change from a
gas to a solid.
• Molecules slow down,
move closer together
and release heat
energy.
Graphing a Phase Change
Melting & Boiling Points
• Melting Point: The temperature at which a
solid changes into a liquid.
• Boiling Point: The temperature at which a
liquid changes into a gas.
• What is a Freezing point? Compare the
freezing and melting points of water.
Summary
Just to review before we start…
What is the melting point of this substance? 50˚C
The boiling point? 100˚C
It takes energy to heat stuff up!
for pure substance in single phase - can
calculate how much E needed using:
Q = mCT
Q = energy in Joules
m = mass in grams
C = specific heat capacity
T = change in temperature = Tf - Ti
on other hand, when something cools down,
energy is released!
Q=
mCliquidT
Temperature
Q=
mCsolidT
I
II
III
Q=
mCgasT
IV
V
C = specific heat capacity
(amount heat required to raise
temp of 1g of pure substance by
1C)
C is a physical constant
Time
unique for every pure
substance
CAN YOU FIND THE SPECIFIC
So, how do we calculate the amount
of energy required during a phase
change?
• HF = Heat of Fusion (Q = mHF)
• HV = Heat of Vaporization (Q=mHV)
• We use one of these two constants
instead of specific heat and delta T
Q = mCT
How much heat is absorbed when 10
grams of ice melts at 0oC?
• Heat absorbed =
mass of substance x heat of fusion of substance
• Q = mHf = (10 g)(334 J/g) = 3340 J
• Where does this energy go?
– Particles must overcome forces of attraction to
move farther apart during phase change (s → l)
It takes a lot more energy to go from liquid to gas
than from solid to liquid. Why?
H2O changing from liquid to gas requires
22,600J/g
H2O changing from solid to liquid requires 3,340J/g
* greater energy required to change from liquid to gas
because particles are spreading farther apart!
Heating curve of H2O
Graphing a Phase Change
– Why is there no change
in temperature during a
phase change?
– Define melting and
boiling points.
– What is the melting
point and boiling point
of water?
– At what temperature
does water freeze and
become a solid?