Transcript Warm-up Copy and answer the questions

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5/11/15 Do Now
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1) Explain how particles transfer
kinetic energy from one particle to
another.
Energy is transferred during collisions.
2) Using what you know about
thermal energy, explain how a
thermos keeps hot coffee hot.
The vacuum prevents particles in the hot
coffee from colliding with particles in the
surroundings. This keeps the energy
within the container.
1) Energy
Ch. 15.1 p. 516-8
a) Energy can be modeled as a substancelike quantity that can be measured and
stored in a physical system.
b) Energy can “flow” or “transfer” from one
system to another and cause physical or
chemical changes.
c) Energy maintains its identity after transfer.
2) Kinetic Molecular Theory (KMT)
Ch. 12.1 p. 402-3
a)Matter is made of tiny particles that are in
constant random motion.
https://www.youtube.com/watch?v=hy-clLi8gHg
b) These particles exert long-range
attractions and short-range repulsions on
one another. Attractions reduce the
energy in the system; repulsions increase
the amount of energy.
c) A hotter sample is one whose molecules
are moving (on average) faster than the
molecules in a colder sample.
3) Storing Energy
a) Thermal energy, Eth – energy of motion.
Eth depends on the mass of the object
and velocity of the particles in the object
b) Phase energy, Eph – energy due to attractions
between molecules. Attractions decrease the
energy of a system.
Gases – weak attractions, high Eph
Solids – strong attractions, low Eph
c) Chemical potential energy, Ech- energy due to
attractions of atoms within molecules. These
attractions are described as chemical bonds
because they are directed between specific atoms
in the molecule.
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Using what you know about thermal
and phase energy, explain why
sweating makes you feel cooler.
When you sweat, water evaporates
and changes from liquid to gas phase.
The water vapor has higher Eph than
liquid water. Energy is transferred
from Eth to Eph and your body
temperature decreases.
Icy Hot : Energy and Phase Changes
1) The purpose is to measure the
temperature of water as it warms and
changes phase from solid to liquid to
gas.
2) Hypothesis - What will the graph of
temperature vs time look like? Draw
a sketch of the curve. Label axes and
include a title.
Energy and phase change
Temp(ºC)
100
0
Time
Icy Hot : Energy and Phase Changes
Icy Hot: 3) Procedures
• Begin taking temperature readings
when you turn on your hotplate.
• Measure temperature every 30 s.
• Before taking each reading, use a
stirring rod to stir for 5 s.
• Heat the water slowly (~350°C/4)
until all the ice has melted. Then,
increase the heating by turning up
your hot-plate.
• Stop taking temperature readings
after your water has been at a
rolling boil for 3 minutes.
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1) How are the structures of solid, liquid, and
gaseous water similar? Different?
2) How does the arrangement of the particles
explain the properties of the phase? Why is
a particular phase rigid or fluid?
3) What forces attract particles to each other?
What forces cause repulsions?
4) Processes that Transfer Energy
a) heating (Q) - transfers energy between
particles through collisions
System what is
being
studied
b) working (W) - transfers energy between
big objects through forces
c) radiating (R) - transfers energy by
emitting or absorbing
photons (light)
surroundings
d) Energy transfers affect both the system and the surroundings.
e) Energy doesn’t mysteriously appear or get lost.
Icy Hot Lab – Clean-up and Analysis
 Clean-up
• Unplug your hotplate. Use tongs to
empty beaker and place on the
table. Make sure the cord is off the
floor and away from the sink.
• Allow beaker to cool. Return
materials to your basket.
4) Analysis - Construct a graph of
temperature vs. time of your data.
Connect the dots with a smooth curve.
Icy Hot Lab – Clean-up and Analysis
4) Analysis - Construct a graph of
temperature vs. time of your data.
Connect the dots with a smooth curve.
From Ice to Steam
B
A
C
Icy Hot: Analysis and Conclusion
Divide your heating curve into three regions; label
(A) a low temperature plateau
(B) a region of temperature change
(C) a high temperature plateau
C
B
A
Answer the following questions on the same paper as your pre-lab.
1. i.
Did a chemical change occur during heating and phase
change? Explain.
ii. Did the system absorb or release energy? Explain.
2. For each region (A, B, and C) on your graph,
i. describe how the energy supplied by the hotplate was
stored by the system (Eth or Eph)
ii. state which phases were present
iii. draw a model at the molecular level that shows how the
water molecules were behaving.
3. How would increasing the rate of heating by turning up the
hotplate affect the shape of the temp. vs. time curve?