Thermodynamics

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Thermodynamics

• Thermo heat
• Dynamics movement

2
Thermodynamics

• Our objectives are to
• define temperature, heat, thermodynamics, and
  entropy
• describe the three methods of heat transfer
• discuss everyday examples to illustrate these
  concepts

3
Temperature Scales
http//www.magnet.fsu.edu/education/tutorials/magn
etacademy/superconductivity101/images/superconduct
ivity-temperature.jpg
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Temperature Conversions

• Tc 5/9 (Tf-32)
• Tf 9/5Tc 32
• Tc TK - 273.15
• TK Tc273.15

5
Applying the formulas (add this to your lab
sheet)

• Use your calculations from Station 1 to confirm
  that your measurements describe the same
  temperature in different units.
• Calculate the water temperature for each beaker
  in Kelvin

6
Kinetic Theory Molecular Interpretation of
Temperature

• Temperature is a direct measure of the average
  molecular kinetic energy
• As temperature increases, molecules increase in
  kinetic energy (move faster)
• Lab example Food coloring diffused more quickly
  in the hot water compared to the room temperature
  water. (Station 2)

http//resources.edb.gov.hk/cphysics/heat/tep/tran
s/kinetic_theory.gif
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• Take one minute to summarize to your partner what
  you learned about temperature.
• Your partner has 30 seconds to summarize/correct
  what you said.
• Switch roles and repeat!

8
Entropy

• The measure of the unavailability of a systems
  energy to do work
• Increased entropy is described as increasing
  disorder, or randomness, in a system

9
Entropy and the Laws of Thermodynamics

• Second Law of Thermodynamics The entropy of an
  isolated system not in equilibrium will tend to
  increase over time
• Third Law of Thermodynamics As temperature
  reaches absolute zero (0 K) entropy of a system
  decreases to its minimum

10

• Take one minute to summarize to your partner what
  you learned about entropy.
• Your partner has 30 seconds to summarize/correct
  what you said.
• Switch roles and repeat!

11
Heat

• Heat is a form of energy
• Also called thermal energy
• Heat moves from an object/area of high
  temperature to an object/area of low temperature
  until thermal equilibrium is reached (both
  objects are the same temperature).

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Lab example Station 3

• Which object has the higher temperature, your
  hand or the ice?
• In which direction will heat flow?
• Why does the ice melt?

13
Zeroth Law of Thermodynamics
If bodies A and B are separately in thermal
equilibrium with a third body, C, then A and B
will be in thermal equilibrium with each other
if placed in thermal contact.
www.taftan.com/thermodynamics/ZEROTH.HTM
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Methods of Heat Transfer

• Conduction direct contact (Station 4)
• Example hand on stove
• Convection movement in gases and liquids
  (Station 5)
• Example Convection currents in ocean
• Radiation electromagnetic waves
• (Station 6)
• Example microwaves in microwaves

15

• Take one minute to summarize to your partner what
  you learned about heat transfer.
• Your partner has 30 seconds to summarize/correct
  what you said.
• Switch roles and repeat!

16
Thermal Expansion
http//www.wbacorp.com/img/products/watertite.jpg

• As temperature increases, molecules within a
  substance move faster (kinetic theory).
• As molecules move faster, they collide more
  frequently causing the substance to expand
• Examples- Station 7, Expansion joints on bridges,
  bimetallic strips in smoke detectors

www.anaheim.net/.../fire/com_svc/sm_det.html
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Water is an exception!Water expands when it
freezes due to hydrogen bonds between water
molecules.
www.conceptualphysics.com/
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• Take one minute to summarize to your partner what
  you learned about thermal expansion.
• Your partner has 30 seconds to summarize/correct
  what you said.
• Switch roles and repeat!

19
Specific heat

• Specific heat is a constant that relates heat and
  temperature change, per kilogram
• Different materials have different specific heat
• A low specific heat means heat is conducted
  through an object quickly
• Station 4-wax melted at different rates because
  spokes were made of different materials

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Heat Absorption

• Station 8
• Dark colors absorb more light (energy), and
  therefore give off more heat (energy) and will
  have a higher temperature
• Light colors reflect more light (energy) and have
  a lower temperature

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Insulation
www.fylde.gov.uk/.../new-insulation-02.jpg

• Materials with a high specific heat are good
  insulators
• Insulators resist heat flow
• Station 9 a thermos keeps liquids hot (or cold)
  sides of thermos are double walled (vacuum in
  between), reflective inner surface reflects heat
  back into liquid
• Examples air, paper, fiberglass, styrofoam,
  wood, glass

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• Take one minute to summarize to your partner how
  you plan to use this information in constructing
  your model home.
• Your partner has 30 seconds to summarize what you
  said.
• Switch roles and repeat!

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Exit ActivityThink-Pair-Share