Thermal Energy

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Thermal Energy

• Transfer and absorption

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Thermodynamics

• Thermodynamics-study of heat transformations
  into other forms of energy

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Heat

• Fire dissipates heat
• Does not absorb heat
• Heat always flows from a hotter to cooler

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Heat flowing from hotter to cooler
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Grease fire

• http//www.gocolumbiamo.com/Fire/Educational/stove
  fires.php
• http//www.teachertube.com/view_video.php?viewkey
  d76c5ec1acefe6d433b6
• http//www.teachertube.com/view_video.php?viewkey
  e0da400d9b98c254b9fc

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Thermal Energy

• Thermal Energy- total energy of the molecules
• Temperature- related to average energy per
  molecule

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Thermal Energy and Temperature

• Temperature-quantifies the average kinetic energy
  of the particles in an object
• The warmer an object the more kinetic energy it
  has.
• KEavgKEt/(number of particles)
• Thermal Energy- proportional to the number of
  particles

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Equilibrium and Thermometry

• Hot particles move faster more thermal energy
• Conduction-transfer of kinetic energy when
  particles collide
• energy transferred from a warmer object to a
  colder object
• How much energy is in an object at 0 Kelvin
  (absolute zero)?
• Scientists put a light wave on hold
• http//www.msnbc.msn.com/id/3077366/

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Equilibrium and Thermometry

• Thermal Equilibrium- the state in which the rate
  of energy flow between two objects is equal and
  the objects are at the same temperature
• Same temperature

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Temperature Scales

• Celsius-
• The zero point is the freezing point of water
• The 100 point is the boiling point of water
• Kelvin
• The zero point is where all thermal energy has
  been removed. No lower possible temperature, No
  motion in the atoms. Absolute Zero
• 0 K - 273.15 C
• Tc 273 TK

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Temperature Scales

• Fahrenheit
• The zero point is determined by a frigorific
  mixture of ice, water, and ammonium chloride (a
  salt). The mixture automatically stabilizes its
  temperature at 0 F
• The second point is the 32 degree found by
  putting the thermometer in still water as ice is
  just forming on the surface.
• The third point, the 96 degree, was the level of
  the liquid in the thermometer when held in the
  mouth or under the armpit. (Has been since
  adjusted to 98.6)

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Three Temperature Scales
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Three Temperature Scales
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Heat

• And how it transferred

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Heat

• Heat-energy that always flows from the hotter
  object to the cooler object.
• Left to itself heat never flows from a colder
  object to a hotter object.
• Variable Q denotes heat
• Q is in joules or J

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Flow of Thermal Energy

• Conduction
• Convection
• Radiation

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Conduction

• Heat is transferred (conducted) through particles
  that are in direct contact with each other.

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Convection

• The motion of fluid in a liquid or gas caused by
  temperature differences
• Hotter fluids/gases rise.
• Cooler fluids/gases sink.
• Real power from nothing but hot air
• http//www.guardian.co.uk/environment/2002/aug/19/
  energy.renewableenergy

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Radiation

• The transfer of energy by electromagnetic waves
• Does not require contact
• Travels at 3x108 m/s
• Nuclear Test Site, Ground Zero

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Specific Heat

• The amount of energy that must be added to a
  material to raise the temperature of a unit mass
  by one temperature unit.

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Heat Transfer

• Q mC?T mC(Tf Ti)
• Q heat
• m mass
• C specific heat
• T temperature
• Temperature intervals for Kelvin and Celsius are
  the same, (i.e. ?T is the same)

3-5 , pg 319
Ex 1, pg318
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Conservation of Energy

• The total energy in an isolated, closed system
  never changes.
• EA EB constant

6-7, pg321
Ex 2, pg321
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Homework

• Pg 322
• 10, 12, 16, 17
• Pg 336
• 37, 39, 50, 52, 53, 57

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Changes of State and the Laws of Thermodynamics

• Change in state changes structure and the way in
  which atoms store thermal energy

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States of matter

• Solid
• Liquid
• Gas
• Plasma

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Change-of-State
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Changes of State
Heat Q in Joules J

• Melting Point
• Heat of Fusion
• QmHf
• Boiling Point
• Heat of Vaporization
• QmHv
• Condensation Point
• Freezing Point

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Thermal energy

• Increase thermal energy
• Increases particle speed
• Causes more freedom of movement

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Change-of-State
All thermal energy added goes to overcome the
forces holding the particles together. The
temperature does not increase
Boiling
Melting
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The First Law of Thermal Dynamics

• Change in thermal energy is equal to the heat
  added minus the work done
• ?UQ-W
• Where
• ?U is the change in thermal energy
• Q is the heat added
• W is the work done

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Efficiency

• W/QH

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How your refrigerator works
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The Second Law of Thermal Dynamics

• Natural processes go in a direction that
  maintains of increases the total entropy of the
  universe.
• Things get more disordered over time, assuming
  time is going forward.

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The Animate and the Inanimate(available on class
website)

• Read Pg 4-8,42
• Explain what it means
• One page write-up

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Entropy

• Entropy the measure of disorder in a system
• Change in Entropy is equal to the heat added
  divided by the temperature in kelvins
• ?SQ/T
• The measure of unavailability of useful energy

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Temperature and Thermal Energy

• Describe thermal energy and compare it to
  potential and kinetic energies.
• Distinguish between temperature and thermal energy

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Burlwood

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Transitional Page
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Elements

• www.animationfactory.com