Thermodynamics!

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Thermodynamics!
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Heat

• Heat is the transfer of energy between two
  objects.
• It is an electromagnetic wave when in the radiant
  form otherwise the vibrations of the atoms and
  molecules transfer heat as internal energy.

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Units of Heat

• The official SI unit is the Joule (J)
• Heat calorie (cal) 4.186 J
• Kilocalorie (kcal) 4186 J
• Food Calorie (C) 4186 J
• British thermal unit (btu) 1055 J
• Therm 105,500,000 J

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Temperature and Energy

• When objects receive or lose heat their
  temperature changes and the internal energy
  changes.
• Types of Internal Energy
• A) Translational
• B) Rotational
• C) Vibrational

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Movement of Heat

• First thing you need to remember is that there is
  NO such thing as COLD, only a lack of heat
• Temperature is the measurement of the average
  kinetic energy of the molecules of a substance
• Heat always moves from warm to cold meaning
  from something with a higher temperature to
  something with a lower temperature

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Thermal Equilibrium

• When two or more substances of different
  temperatures are mixed or combined, the heat from
  the warmer object will move to the cooler object
  until the temperature of both are balanced.
• The temperature at Thermal Equilibrium will be
  lower than the initial of the warmer object and
  higher than the initial of the cooler object.

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Temperature Conversions

• There are three equations for temperature
  conversions that are important to know in this
  section.
• TF 9/5 Tc 32.0
• Tc 5/9(TF - 32.0)
• TK TC 273.15

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Independent Practice

• F to C
• 50 F
• 25 F
• 88 F
• -5 F
• 0 F

• C or F to K
• 10 C
• 10. F
• 25 F
• 50 C
• 75 C

• C to F
• 27 C
• 87 C
• 2 C
• -10. C
• 12 C

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Answers

• C to F
• 27 C 81 F
• 87 C 190 F
• 2 C 40 F
• -10. C 14 F
• 12 C 54 F

• F to C
• 50 F 10 C
• 25 F -3.9 C
• 88 F 31 C
• -5 F -20 C
• 0 F -20 C

• C or F to K
• 10 C 300 K
• 10. F 260 K
• 25 F 270 K
• 50 C 300 K
• 75 C 350 K

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Heat Transfer
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Convection

• The transfer of heat through the movement of
  liquids and gases
• Ex turbulence, climate changes, wind, boiling
  water

Hot water rises, cools, and falls.
Heated air rises, cools, then falls. Air near
heater is replaced by cooler air, and the cycle
repeats.
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Ocean Convection CurrentsThermal Image
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Ocean Convection Currents
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Sea Breeze

• Solar radiation reaching the earth causes the
  land to warm which in turn warms the air
  (atmosphere) above the land.
• Due to greater density, land masses warm faster
  than bodies of water. Air above the land warms
  faster, rises, and pulls cooler air from over
  water onto the land, creating what is called an
  on-shore (sea) breeze.

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Offshore Breeze

• When the water adjacent to a land mass is warmer,
  air above the water warms faster, rises, and
  pulls air above the land off the shore. This is
  called an off-shore breeze.

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Conduction

• The transfer of heat through touch (direct
  contact)

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Radiation

• The transfer of heat through electromagnetic waves

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Calculating the Sun's Temperature What is the
Sun's temperature? (Assume the Sun's emissivity
(e) is 1.) Distance from Sun to Earth R
1.5 x 1011 m Area of sphere of radius R
4pR2 H 1000 x 4pR2 2.83 x 1026 J/s Radius
of the Sun r 6.9 x 108 m Surface area of the
Sun A 4pr2 5.98 x 1018 m2 esAT4 H s
5.67 x 10-8 SI units T H/(esA)1/4 5375
K http//sol.sci.uop.edu/jfalward/heattransfer/he
attransfer.html
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Specific Heat

• Every substance has a unique specific heat
  capacity (Cp)
• The specific heat is the amount of energy
  required to raise 1 g of a substance 1 C
• The amount of energy to raise or lower the
  temperature of a substance
• Q mCp?T

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Latent Heat

• The heat required during a phase change.
• Q mLf/v (fusion or vaporization)

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Thermodynmaics

• the study of heat and how it is used to do work.
• The internal energy of a substance can be used to
  do work.
• Heat and work can be transferred to or from a
  system.

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Work

• Specifically, we are going to look at the work
  done by a gas.
• W -P?V
• P Pressure (Pa)
• ?V change in volume (m3)
• When work is done by (does, expand) the system
  the work is negative (losing energy).
• When work is done on (compressed) a system work
  is positive (gaining energy).

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The First Law of Thermodynamics

• U Q W
• U Internal Energy
• Q Heat
• W Work
• Unit for all is J
• Energy is conserved
• When heat is added, Q is positive
• When heat is removed, Q is negative

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Types of Thermodynamic Processes

• Isovolumetric the volume of a system remains
  constant
• If ?V 0, then W 0
• If W 0, then U Q

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Types of Thermodynamic Processes

• Isothermal The temperature of the system
  remains constant
• ?U 0
• Adiabatic no energy is transferred to or from
  the system (happens very quickly)
• Q 0 , ?U W

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The Second Law of Thermodynamics

• No cyclic process that converts heat into work is
  100 possible.
• When energy is used to do work, some energy will
  always be turned into unusable heat that is lost
  to the universe
• Entropy the measure of randomness or disorder
  of a system (S)
• The entropy of the universe is always increasing.