Chapter 16

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Chapter 16 Thermal Energy and Heat

• Jennie L. Borders
• Modified by Mrs. Rawls

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Section 16.1 Thermal Energy and Matter

• In the 1700s most scientists thought that heat
  was a fluid called caloric that flowed between
  objects.
• Todays calorie, a
• unit of heat energy,
• comes from this.

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Count Rumford

• Rumford discovered that the heat was a result of
  the motion of the drill, not a form of matter.

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Work and Heat

• Heat is the transfer of thermal energy from one
  object to another because of a temperature
  difference.
• Heat flows spontaneously from hot objects to cold
  objects.

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Temperature

• Temperature is a measure of how hot or cold an
  object is compared to a reference point.
• Temperature is related to the average kinetic
  energy of the particles in an object due to their
  random motions through space.
• As an object heats up, its
• particles move faster, on
• average.

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Thermal Energy

• Thermal energy is the total potential and kinetic
  energy of the particles of an object.
• Thermal energy depends on the mass, temperature,
  and phase (solid, liquid, or gas) of an object.
• Thermal energy, unlike temperature depends on
  mass.

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Thermal Contraction

• Slower particles collide less often and exert
  less force, so pressure decreases and the object
  contracts.

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Thermal Expansion

• Thermal expansion is an increase in the volume of
  a material due to a temperature increase.
• Gases expand more than liquids, and liquids
  usually expand more than solids.

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Thermal Expansion

• Thermal expansion is used in glass thermometers.
• As temperature increases, the alcohol (or
  mercury) in the tube expands and its height
  increases.

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Specific Heat

• Specific heat is the amount of heat needed to
  rise the temperature of one gram of a material by
  one degree Celsius.
• The lower the materials specific heat, the more
  its temperature rises when a given amount of
  energy is absorbed by a given mass.

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Specific Heat

• Formula for Specific heat
• Q m x c x DT
• Q heat (J)
• m mass (g)
• c specific heat (J/goC)
• DT change in temperature final initial (oC)

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Sample Problem

• An iron skillet has a mass of 500.0g. The
  specific heat of iron is 0.449 J/goC. How much
  heat must be absorbed to raise the skillets
  temperature by 95.0oC?
• Q m x c x DT
• m 500.0 g
• c 0.449 J/goC
• DT 95.0oC
• Q (500.0g)(0.449 J/goC)(95.0oC) 21,327.5J

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Practice Problems

• How much heat is needed to raise the temperature
  of 100.0g of water by 85.0oC?
• How much heat in kJ is absorbed by a 750g iron
  skillet when its temperature rises from 25oC to
  125oC?

Q (100.0g)(4.18J/goC)(85.0oC) 35,530J
DT 125oC 25oC 100oC Q (750g)(0.449J/goC)(1
00oC) 33,675J K h d u d c m
33,675J 33.7kJ ? ? ?
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Calorimeter

• A calorimeter is an instrument used to measure
  changes in thermal energy.
• A calorimeter uses the principle that heat flows
  from a hotter object to a colder object until
  both reach the same temperature.
• According to the law of conservation of energy,
  the thermal energy released by a test sample is
  equal to the thermal energy absorbed by its
  surroundings.

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Calorimeter
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Section 16.2 Heat and Thermodynamics

• Conduction is the transfer of thermal energy with
  no overall transfer of matter.
• Conduction occurs between materials that are
  touching.
• Conduction in gases is slower than in liquids and
  solids because the particles in a gas collide
  less often.

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Conduction

• In metals, conduction is faster because some
  electrons are free to move about.

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Conductors

• A thermal conductor is a material that conducts
  thermal energy well.
• Examples silver, copper, gold, aluminum, iron,
  steel, brass, bronze, mercury, graphite, dirty
  water, and concrete.

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Insulators

• A material that conducts thermal energy poorly is
  called a thermal insulator.
• Examples glass, rubber, oil, asphalt,
  fiberglass, porcelain, ceramic, quartz, cotton,
  paper, wood, plastic, air, diamond, and pure
  water.

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Convection

• Convection is the transfer of thermal energy when
  particles of a fluid move from one place to
  another.
• A convection current occurs when a fluid
  circulates in a loop as it alternately heats up
  and cools down.

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Convection

• Convection currents are important in many natural
  cycles, such as ocean currents, weather systems,
  and movements of hot rock in Earths interior.

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Radiation

• Radiation is the transfer of energy by waves
  moving through space.
• All objects radiate energy. As an objects
  temperature increases, the rate at which it
  radiates energy increases.

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Thermodynamics

• The study of conversions between thermal energy
  and other forms of energy is called
  thermodynamics.

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1st Law of Thermodynamics

• The first law of thermodynamics states that
  energy is conserved.

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2nd Law of Thermodynamics

• The second law of thermodynamics states that
  thermal energy can flow from colder objects to
  hotter objects only if work is done on the
  system. (Disorder in the universe is always
  increasing.)

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3rd Law of Thermodynamics

• The third law of thermodynamics states that
  absolute zero cannot be reached.