3.3 Definitions & Notes
PHASE CHANGES
WORDS FOR DEFINITIONS YOU NEED ARE IN RED
Phase Heat of Heat of Endothermic exothermic change fusion vaporization vaporization Evaporation Vapor condensation sublimation pressure 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 The transition from solid to liquid Melting Heat is absorbed by substance or added to substance The transition from liquid to solid Freezing Heat is given off by substance or absorbed by the surroundings The transition from Gas to liquid Condensation Heat is given off by substance or absorbed by the surroundings The transition from Liquid to Gas AT the Boiling point Vaporization Heat is absorbed by substance or added to substance
The transition from Liquid to Gas BELOW the Boiling Evaporation point Heat is absorbed by substance or added to substance
THE TRANSITIONS WE MAY NOT ALREADY KNOW
TRANSITION Description The transition from solid directly to gas SUBLIMATION Heat is absorbed by substance or added to substance Example? The transition from gas directly to solid DEPOSITION Heat is given off by the substance or taken away Example?
Data from Melting/Freezing Lab done with Napthalene
TEMPERATURE CHANGING
Do I need to write this down? Write down what you need.
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. EVAPORATION
What are the best conditions for evaporation to occur?
Air Temperature? Humidity? Water Temperature? Container? Open with a high surface area
Sublimation of Dry Ice (Frozen Carbon Dioxide) http://www.youtube.com/watch?v=WGD-5FfqOws
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 Stays as a Solid Strong constant rate C Increasing Constant Transition Breaking D Increasing Increasing Liquid Weak E Increasing Constant Transition Breaking F Increasing Increasing Gas None
NAME Description LATENT HEAT OF The energy required to make the transition C between liquid and solid phase. Latent FUSION because there is no temperature change. LATENT HEAT OF The energy required to make the transition E between liquid and gas phase. Latent VAPORIZATION because there is no temperature change.
STUDENT NOTES- THE TRANSITIONS WE ALREADY KNOW
TRANSITION Description
Melting
Freezing
Condensation
Vaporization
Evaporation
THE TRANSITIONS WE MAY NOT ALREADY KNOW
TRANSITION Description
SUBLIMATION
DEPOSITION
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