### Energy

```Unit 3- Energy Notes
Model so far… Unit 1
Model so far… Unit 2
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Over the next week copy Model 2 onto your Model
So Far… handout.
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Key Concept 1: When matter- In any of its three
states– gets hot, Its particles go faster and take up
more space, and the solid, liquid or gas expands.
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Key Concept 2: When matter- In any of its three
states– gets cold, Its particles go slower and take up
less space, and the solid, liquid or gas contracts.
How a thermometer works.
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A thermometer works because of the expansion and
contraction of alcohol. The substance found in classroom
thermometer.
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Key Concept 3: The expansion of a substance can
therefore be used to measure temperature itself. A device
which does this is called a “hotness-meter” or
thermometer.
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Key Concept 4: On the Celsius scale thermometer, the
level to which the alcohol (or mercury) contracts at the
freezing point of water is labeled 0 C, and the level to
which alcohol expands at boiling point of water is labeled
100 C.
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Heat Transfer by Conduction
Hotness….
Hotness….
Hotness….
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Key Concept 5:
Post it Challenge
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Write one sentence that shows how energy,
temperature and heat are related.
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Put your name on the back and come stick it to the
board.
Closure
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The system with the most heat will burn you the
worst (200mL boiling water). Write the question
below and think!
Why can dry ice, solid CO2 burn you, but CO2 in the
gas phase cannot? Gases have more kinetic energy
then liquids or solids.
Energy
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Key Concept 6 :Energy is the stuff that
make particle do stuff.
Problem with Energy in Education
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Treatment of energy is inconsistent from discipline to
discipline.
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Students cannot use energy to adequately describe or
explain everyday phenomena.
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Students are taught that energy comes in different forms
or types.
Energy
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When “changing one form of energy into another”1
implies that there are different “kinds” of energy
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“Forms of energy” - implies that somehow energy is
changing
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This makes it difficult for students to describe the
changes in matter.
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Remember: HOMEWORK- DUE FRIDAY
1- American Association for the Advancement of Science, Project 2061 Benchmarks Online,
1,2, 3’s of eNeRGy
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Key Concept 7:
Why does a solid have a definite shape?
Icy Hot Lab
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Will not be done in your Lab Notebook.
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Key Concept 8: Goal of Icy Hot Lab: How does the
temperature of water change when energy is
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My Notes
Temp and time when all ice was melted:
Temp and time when the water started to boil:
Any other important notes/observation
Icy Hot Board Meeting
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1.
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•
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Divide your heating curve into three regions (A,B, and C); label
each region:
(A) a low temperature plateau
(B) a region of temperature change
(C) a high temperature plateau
2.
State what phases were present at A, B, and C
3.
Draw a model at the particle level that shows how the water
particles were behaving.
4.
How does your groups final white board compare to your
prediction (Key Concept 9).
Icy Hot Board Meeting
Icy Hot Discussion
Why does a solid have a definite shape?
Intermolecular Forces
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There are forces of attraction and repulsion that
exist between particles (molecular) of all
substances.
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These intermolecular forces allow molecules to pack
together in the solid and liquid states.
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Key Concept 10: All phase changes involve either
an increase or decrease of intermolecular forces. In
temperature plateaus went to break up these
intermolecular forces.
Intermolecular Forces
Icy Hot Conclusion Questions
Room Number is: 169429
For each of the phase changes below, choose whether
intermolecular forces increase or decrease.
Phase Change
Name
Intermolecular Forces
Increase or Decrease
1) Solid to Liquid
Melting or Fusion
(T) Increase
(F) Decrease
2) Liquid to Gas
Evaporation or
Vaporization
(T) Increase
(F) Decrease
3) Gas to Solid
Deposition
4) Liquid to Solid
Freezing or
crystallization
(T) Increase
(F) Decrease
(T) Increase
(F) Decrease
Intermolecular Forces
In a phase change, does the distance
between molecules increase or decrease?
When considering phase changes, the
closer molecules are to one another, the
stronger the intermolecular forces.
Key Concept 11: Heating Curve
Key Concept 12: Cooling Curve
Room Number is: 169429
1.
In what part of the curve would
substance X be a liquid?
2.
In what part of the curve would
substance X be a solid?
3.
What part of the curve represents a
mixed liquid/gas phase of substance
X?
4.
What is the melting temperature of
substance X?
5.
What is the boiling temperature of
substance X?
Room Number is: 169429
What is the boiling point of the
substance?
(a) 0°C
(c) 12°C
(b) −50°C
(d) 75°C
What state of matter is the substance
at 50°C?
(a) gas
(c) solid
(b) liquid
(d) not enough
information
Energy Bar Charts
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Better know as:
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Key concept 13: Energy bar charts are how we can
represent the role of energy when a system is
changed.
Constructing an Energy Bar Chart
Consider this example
A cup of hot coffee cools as it sits on the table.
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1.
Determine what is in the system
cup
coffee
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Everything else makes up the surroundings
Decide whether Ech is involved
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coffee; particles are not rearranged to form new
substances
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So, ignore Ech for now.
Assign values to Eph
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Key Concept 14: Due to interactions between
particles, the energy stored due to the
arrangement of particles is ranked:
solids < liquids < gases
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We choose to represent these phases by using:
Solids = 1 bar
Liquids = 2 bars
Gases = 4 bars
Assign values to Eph
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Use two Eph bars before and after
Choose bars for Eth depending on temperature
•
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Use 4 bars for hot coffee and 2 bars for room temp
coffee
Other values might also work; try to be consistent in
Now show energy transfer
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Final situation has 2 less bars of E than initial; 2
bars had to leave the system
Now, consider phase change
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A tray of ice cubes (-8 ˚C) is placed on the counter and
becomes water at room temperature
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What do we know about the situation?
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The system is the tray of ice cubes.
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The solid water turns to liquid water - no change in Ech
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The Eph increases (solidliquid)
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The Eth increases (temp rises)
Now represent these changes in bar graph.
Initial & Final States
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Choice of bars for Eth arbitrary, but consistent.
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I generally use 2 bars for room temp and one bar for
cold liquid, -8˚C should be < 1 bar.
Account for Energy
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Energy must flow into system via heating
Q= Energy
Q= Energy
Bellringer
How much Q?
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We are now interested in learning just how much
energy transferred during these changes.
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Update our initial thought trifold again.
White Board Questions
With your desk partner pick one of the three demos
board. (Demo1: Red, Demo 2: Blue, Demo 3: Green)
1) What demo are you going to describe?
cubes) gain or lose heat?
3) Did the objects gain or lose heat at the same rate?
White Board Questions
4) What do you think accounts for the different rates of
energy transfer (or heating)?
5) Imagine you are given 1g of copper and 1g of wood
at room temperature. If you wanted to raise that 1g
sample 1C° which substance would require more
energy?
Quick review
Units of Energy
Measuring Energy
• Key Concept 15:A calorie is defined as the
amount of energy required to raise the
temperature of one gram of water one
degree Celsius.
• Food is measured in Calories, or 1000
calories (kilocalorie).
• Key Concept 16 :A joule is the SI unit of heat
and energy, equivalent to 0.2390 calories.
Specific Heat
• Key Concept 17:The specific
heat of any substance is the
amount of heat required to raise
one gram of that substance one
degree Celsius.
• Some objects require more
heat than others to raise their
temperature.
Specific Heat
Key Concept 18: Specific Heat is an intrinsic property,
it is independent of how much of the material is
present.
Specific Heat
Demo1-
Water: 4.184 J/gC
Air: 1.02 J/gC
Demo 2-
Plastic- 2.3 J/gC
Steel: 0.46 J/gC
Demo 3-
Copper: 0.386 J/gC
Wood: 0.6 J/gC
White Board Questions
Move your desk into desk pods. Let the duel begin.
5) What the specific heat for wood and copper in a
complete sentence.
Copper: 0.386 J/gC
Wood: 0.6 J/gC
White Board Questions
6) If you had 10 grams of copper and wanted to raise it
10 degree C, how much energy would that take? The
specific heat of copper is 0.386 J/gC.
White Board Questions
6) If you had 10 grams of copper and wanted to raise it 10 degree C,
how much energy would that take? The specific heat of copper is
0.386 J/gC.
7) What is I wanted to decrease the temperature of 10 gram sample of
copper 10 degree C? How much energy would need to be removed?
Desk Pod Challenge
As a desk pod combine your thoughts and solve this
problem. Show all your work on one of the white board.
Please, draw a picture to help illustrate how you came to