Phase Changes and Heating Curves 2016.notebook
October 14, 2016
Phase Changes
Endothermic and Exothermic Aim: To determine what is occurring on the molecular level during a phase change
Oct 6­1:47 PM
Phase Changes
All phase changes occur at constant temperature. Therefore average kinetic energy remains constant.
The energy that is changing during a phase change is potential energy.
During a phase change, the heat added (PE increases) or released (PE decreases) will allow the molecules to move apart or come together.
Nov 6­5:51 PM
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Phase Changes and Heating Curves 2016.notebook
October 14, 2016
Phase Changes
Fusion (melting): solid to a liquid
Solidification (freezing): liquid to a solid
Boiling (vaporization): liquid Condensation: gas to a liquid
to a gas
Sublimation: solid to a gas
Deposition: gas to a solid
Nov 6­5:51 PM
Endothermic Phase Changes
Exothermic Phase Changes
4. Freezing(solidification): s to l
1. Melting(fusion): s to l
2. Boiling(vaporization): l to g
5. Condensation: l to g
3. Sublimation: s to g
6. Deposition: g to s
Heat absorbed causes the molecules Heat released allows the molecules to move closer together and the to move farther apart by overcoming the intermolecular forces of attraction. intermolecular forces of attraction become stronger.
Oct 6­1:49 PM
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Phase Changes and Heating Curves 2016.notebook
October 14, 2016
Phase Equilibrium
Phase equilibrium­ when two phases exist at the same time during a phase change.
Fusion and Solidification occur at the same temperature for a substance.
Melting(fusion) ­­­>
H2O (s) <­­> H2O (l)
<­­­ freezing(solidification)
Vaporization and Condesnation occur at the same temperature for a substance.
vaporization­­­>
H2O (l) <­­> H2O (g)
<­­­ condensation
Oct 6­2:06 PM
Nov 16­8:29 AM
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Phase Changes and Heating Curves 2016.notebook
October 14, 2016
Heating and Cooling Curves
• Shows the temperature of each phase change. (flat line)
• Shows the boiling point and melting point of a substance.
• Can be used to determine the phase of matter at a given temperature.
• Can be used to determine if the substance needs more energy to melt (fusion) or boil (vaporize).
Oct 6­1:49 PM
D
E
C
B
A
Oct 6­7:24 PM
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Phase Changes and Heating Curves 2016.notebook
October 14, 2016
1.
At what temperature does the substance begin to melt?
2.
What temperature does it boil?
3.
At which section is the substance a solid? liquid? gas?
4.
What sections of the graph have constant kinetic energy?
5.
What sections of the graph have constant potential energy?
Oct 6­7:25 PM
Temperature (C)
Model 2: Temperature of a Substance as Heat is Added Over Time
Time increasing ­­>
Oct 6­7:00 PM
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Phase Changes and Heating Curves 2016.notebook
October 14, 2016
Practice Problems
Oct 6­5:25 PM
Practice Problems
Oct 6­5:26 PM
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Phase Changes and Heating Curves 2016.notebook
October 14, 2016
Oct 8­7:32 AM
Oct 8­7:31 AM
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