Thermodynamics
From the Greek thermos meaning heat and dynamis meaning
power is a branch of physics that studies the effects of changes
in temperature, pressure, and volume on physical systems at the
macroscopic scale by analyzing the collective motion of their
particles using statistics.
‰ Thermodynamics describes how systems respond to changes in
their surroundings.
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This can be applied to a wide variety of topics in science and
engineering, such as engines, phase transitions, chemical reactions,
transport phenomena, and even black holes.
The results of thermodynamics are essential for other fields of
physics and for chemistry, chemical engineering, cell biology,
biomedical engineering, and materials science to name a few.
Module 3 - Thermodynamics
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Molecular Basis of Thermodynamics
Vapor Pressure, Humidity, Mean Free Path, Diffusion
Chapter 19
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Temperature, Thermal Equilibrium, Expansion, Stresses
Ideal Gases
Chapter 18
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The starting point for most thermodynamic considerations are the
laws of thermodynamics, which postulate that energy can be
exchanged between physical systems as heat or work.
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Chapter 17
Heat
1st Law of Thermodynamics
Chapter 20
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Cycles – Engines
2nd Law of Thermodynamics - Entropy
Wikipedia: http://en.wikipedia.org/wiki/Thermodynamics
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Temperature and Thermal Equilibrium
Measuring Temperatures
The zeroth law of thermodynamics:
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If two systems are each in thermal equilibrium with a
third, then they are in thermal equilibrium with one
another.
If two thermal systems are in thermal equilibrium with
one another, then they have the same temperature.
Temperature is a way of determining
(measuring?) thermal equilibrium
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Two systems have the same temperature
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They are in thermal equilibrium
Two systems have different temperatures
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The are NOT in thermal equilibrium
Thermometer: a device that measures
temperature quantitatively
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Minimal effect on system being measured
Good contact with system being measured
Reproducible and easily read scale
Properties useful for thermometry:
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Thermal expansion of fluids and solids
Pressure of gases
Reflective properties
Electric and magnetic properties
Color
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Some Thermometers
Temperature Scales
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Fahrenheit:
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tF = 32° at freezing point of water
tF = 212° at boiling point
Celsius:
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tC = 0° at freezing point of water
tC = 100° at boiling point
Thermal Expansion
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Solids expand when temperature increases;
describe by coefficient of thermal expansion (α):
For fluids, use coefficient of volume expansion (β)
instead (as length is not well-defined):
You want to insert an aluminum rod, which at 20.0°C has a radius of 1.00020
cm into a copper tube which has a radius of 1.00010 cm at the same
temperature. You decide to put both of them in the refrigerator. At what
temperature will the rod just fit if both are cooled to the same temperature?
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Thermal Stress
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Induced stress when the material does not freely
expand or contract due to a temperature change
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The material is “restricted” in some manner
An aluminum rod 1.50 m long and with a cross-sectional area of 1.50 ×
10-6m2 is heated to 300°C and clamped at both ends. The temperature
of the rod is then lowered 20.0°C. As a result, the rod would normally
contract, but it is prevented from doing so by the clamps. What is the
tension in the rod? For aluminum, the coefficient of thermal expansion
is 23.0 × 10-6 oC-1 and the value of Young's modulus is 7.00 × 1010 Pa.
ΔL = LoαΔT
But
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ConcepTest
Freezing Cold
ConcepTest
1) yes, at 0 °C
It turns out that – 40°C is the same
temperature as – 40°F. Is there a
temperature at which the Kelvin and
Celsius scales agree?
ConcepTest
2) yes, at -273 °C
3) yes, at 0 K
4) no
Glasses
ConcepTest
stuck, one inside the other.
How would you get them
unstuck?
Steel Expansion I
A steel tape measure is
marked such that it gives
accurate length measurements 1) measured lengths will be too small
at room temperature. If the
2) measured lengths will still be accurate
tape measure is used outside
on a very hot day, how will its 3) measured lengths will be too big
length measurements be
affected?
1) run hot water over them both
Two drinking glasses are
Thermometers
1) the mercury contracts before the
You may notice that if a
glass contracts
mercury-in-glass thermometer 2) the glass contracts before the
mercury contracts
is inserted into a hot liquid, the
3) the mercury contracts before the
mercury column first drops,
glass expands
and then later starts to rise (as
4)
the
glass expands before the
you expect). How do you
mercury expands
explain this drop?
5) the mercury expands before the
glass contracts
2) put hot water in the inner one
3) run hot water over the outer one
4) run cold water over them both
5) break the glasses
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ConcepTest
ConcepTest
Steel Expansion II
Metals such as brass expand when
heated. The thin brass plate in the
movie has a circular hole in its
center. When the plate is heated,
what will happen to the hole?
Steel Ring I
A steel ring stands on edge with a rod of
some material inside. As this system is
heated, for which of the following rod
materials will the rod eventually touch
the top of the ring?
1) gets larger
2) gets smaller
3) stays the same
4) vanishes
1) aluminum
2) steel
3) glass
4) aluminum and steel
5) all three
Quartz
Glass Steel Al
10−6
10−5
Hg
10−4
Air
10−3
Coefficient of volume expansion β (1/°C )
ConcepTest
Steel Ring II
You want to take apart a couple of
1) heat the thing up
aluminum parts held together by
2) cool the thing down
steel screws, but the screws are
ConcepTest
A grandfather clock uses a brass
pendulum to keep perfect time at
1) clock will run slower than usual
room temperature. If the air
2) clock will still keep perfect time
conditioning breaks down on a
very hot summer day, how will the 3) clock will run faster than usual
grandfather clock be affected?
3) blow the thing up
stuck. What should you do?
Quartz
10−6
Glass Steel Al
10−5
10−4
Hg
Grandfather Clock
Air
10−3
Coefficient of volume expansion β (1/°C )
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