Thermal Energy

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Chapter 12 Thermal Energy
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12.1 Temperature
Thermodynamics is a Study of heat.
A major topic of in this field Is the
Kinetic-Molecular Theory.
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The kinetic-molecular theory Is based on the
assumption that In a hot body, the particles Move
faster and thus have More kinetic energy. And
Vise-Versa.
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The overall energy of motion of The particles
that make-up An object is called the Thermal
energy of that object.
THIS IS DIFFERENT THAN TEMPERATURE!!
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What do you use to measure Temperature?
Maybe a thermometer?
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An Italian physicist invented The very first
thermometer, Who was he?
Galileo Galilei
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Temperature is the hottness Of an object as
measured Using a specific scale.
A device that measures temperature is called A
thermometer.
Heat always flows from hot to cold.
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The choice of a temp. Scale is quite arbitrary.
One popular one was invented By Gabriel
Fahrenheit.
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He devised his own scale. Do you know what it is?
Duh, Fahrenheit!
His thermometer were popular, So his system was
as well.
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After a while a different scale Was accepted by
Scientists.
It was called Celsius, Invented by Anders Celsius
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The Celsius scale was the First major scale to
Place the freezing point of Water at 0, and
the Boiling point at 100.
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A few correlations
0C 32F
Melting ice
Normal body temp.
37C 98.6F
Boiling water
100C 212F
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The newest temp. scale Is the Kelvin scale.
The Kelvin scale is the SI Scale accepted by
scientists
It was invented by William Thomson, Lord Kelvin
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The difference between the Celsius and Kelvin
scales Is very small.
It has to deal with the Zero point.
0 Kelvin is the absolute zero, Or -273.15 C
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At absolute zero, all Kinetic energy stops!
Though theoretically possible, It can never be
reached, So far.
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A few conversions, shall we.
F 9/5 C 32
C 5/9 X (F 32)
K C 273
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Lets try some
163C ? F
325F
50 K ? C
-223C
-40 F ? C
-40C
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Convection is the transfer Of heat by means of
Motion in a fluid.
Radiation is the transfer Of energy by
electromagnetic Waves.
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Specific heat is the amount of Energy that must
be added to a Material to raise the
temperature Of a unit mass one Temperature unit.
Q mC?T
Q heat C specific heat
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PROBLEMS...
A 0.4 kg block of iron is Heated from 295 K to
325 K. How much heat had to be Transferred to
the iron?
Q 540 J
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Conduction is the transfer of Kinetic energy
when Particles collide.
Thermal equilibrium is a state Where the rate of
energy Transfer between bodies Becomes equal
and the bodies Will thus have the same
Temperature.
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12.2 Change of State Laws of Thermodynamics
There are 4 states of matter What are they?
Solid Liquid Gas Plasma
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So how can you go from One state to another?
By changing the temperature.
Heating or cooling can cause Boiling, freezing,
sublimation, Etc.
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The energy required to melt a Substance goes
into Rearranging the molecules.
The heat of fusion is the energy Per unit mass
transferred in Order to change a substance From
liquid to solid at a Constant temperature And
pressure.
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The heat of vaporization is the Energy per unit
mass Transferred in order to change From a
liquid to a vapor At constant temperature And
pressure.
Latent heat is the energy per unit Mass that is
transferred during A phase change of a substance.
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There are formulas to find The amount of heat
used By the heats of fusion and Vaporization.
Q mHv
Q mHf
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PROBLEMS...
Catherine is asked to melt 0.1 kg of ice at its
melting Point and warm the resulting Water to
20.0 C. How Much heat is needed?
Q 41.8 kJ
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First Law of Thermodynamics
The energy of the universe is constant.
(comes from the law of conservation of energy)
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Your book says it like this
The first law of thermodynamics States that the
total increase In thermal energy of a system Is
the sum of the heat added To it and the work done
on it.
?U Q - W
U Internal energy Q Heat W Work
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Signs of Q W for a system
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Problems...
A total of 135 J of work is done on A gaseous
refrigerant as it Undergoes compression. If the
Internal energy of the gas increases By 114J
during the process, what Is the total amount of
energy Transferred by heat? Has energy Been
added to or removed from The system?
Q -21 J
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The second law of thermodynamics States that the
entropy of The universe is always Maintained or
increased.
Entropy is the measure of Disorder of a system.
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The second law can Also be stated as
No machine can be made that Only absorbs energy
by heat And then entirely transfers the Energy
out of the engine by An equal amount of work.
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Increasing disorder reduces The energy available
for work.
Greater disorder means there Is less energy to
do work.
Entropy can increase or Decrease within a system.
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Q T
?S
S Entropy Q Heat T Temperature in Kelvins
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THE END