3.3 Definitions & Notes
PHASE CHANGES
WORDS FOR DEFINITIONS YOU NEED ARE IN RED
Phase
change
Heat of
fusion
Heat of
vaporization
Endothermic
exothermic
vaporization
Evaporation
Vapor
pressure
condensation
sublimation
deposition
PHASE CHANGE: thermal energy (HEAT) is transferred to or from a substance that causes a
change in phase.
During a phase change the temperature of the substance does not change
A phase change is reversible ( can be undone or the substance can be returned to its
original state)
Phase change is a physical change, NOT A CHEMICAL CHANGE.
Why doesn’t temperature change during a phase change?
The thermal energy is consumed while breaking bonds.
EXAMPLES:
Ice absorbs heat to melt to liquid water.
Liquid water gives off heat and freezes.
TRANSITION: when a substance is moving from one phase to another it is in TRANSITION
As a verb “ A substance is transitioning” – changing.
EXO THERMIC: when heat is given off (Ex means – outside)
ENDO THERMRIC: when heat is taken in
THE TRANSITIONS WE ALREADY KNOW
TRANSITION
Description
Melting
The transition from solid to liquid
Heat is absorbed by substance or added to substance
Freezing
The transition from liquid to solid
Heat is given off by substance or absorbed by the
surroundings
Condensation
The transition from Gas to liquid
Heat is given off by substance or absorbed by the
surroundings
Vaporization
The transition from Liquid to Gas AT the Boiling point
Heat is absorbed by substance or added to substance
Evaporation
The transition from Liquid to Gas BELOW the Boiling
point
Heat is absorbed by substance or added to substance
THE TRANSITIONS WE MAY NOT ALREADY KNOW
TRANSITION
Description
SUBLIMATION
The transition from solid directly to gas
Heat is absorbed by substance or added to substance
Example?
DEPOSITION
The transition from gas directly to solid
Heat is given off by the substance or taken away
Example?
Data from Melting/Freezing Lab done with Napthalene
HIDDEN ENERGY
In this flat section the energy is not changing the temperature.
The temperature is constant. Where is it going?
During this time the Heat is being used to break the bonds so the material
transitions from liquid to solid.
People studying this originally called this the hidden heat because the heat
seemed to be disappearing. They used the term LATENT to describe it. This
comes from the Latin word Lateo which means lie hidden| lurk; live a
retired life| escape notice.
TEMPERATURE CHANGING
Do I need to write this down?
Write down what you need.
ENERGY PHASE DIAGRAMS
WHAT IS HAPPENING IN THIS GRAPH ENERGY IS ADDED (Moving left to right)?
Energy
Temp
Phase
Bonds
A
None
Absolute Zero
?
?
B
Increasing
Increases at a
constant rate
Stays as a Solid
Strong
C
Increasing
Constant
Transition
Breaking
D
Increasing
Increasing
Liquid
Weak
E
Increasing
Constant
Transition
Breaking
F
Increasing
Increasing
Gas
None
NAME
Description
C
LATENT HEAT OF
FUSION
The energy required to make the transition
between liquid and solid phase. Latent
because there is no temperature change.
E
LATENT HEAT OF
VAPORIZATION
The energy required to make the transition
between liquid and gas phase. Latent
because there is no temperature change.
BEST CONDITIONS FOR EVAPORATION
ENERGY PHASE DIAGRAMS
WHAT IS HAPPENING IN THIS GRAPH ENERGY IS ADDED (Moving left to right) ?
Energy
Temp
Phase
Bonds
A
B
C
D
E
F
C
LATENT HEAT OF FUSION
E
LATENT HEAT OF
VAPORIZATION
