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Chapter 16

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Chapter 16 Thermal Energy and Heat Jennie L. Borders Modified by Mrs. Rawls Section 16.1 Thermal Energy and Matter In the 1700 s most scientists thought ... – PowerPoint PPT presentation

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Title: Chapter 16


1
Chapter 16 Thermal Energy and Heat
  • Jennie L. Borders
  • Modified by Mrs. Rawls

2
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.

3
Count Rumford
  • Rumford discovered that the heat was a result of
    the motion of the drill, not a form of matter.

4
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.

5
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.

6
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.

7
Thermal Contraction
  • Slower particles collide less often and exert
    less force, so pressure decreases and the object
    contracts.

8
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.

9
Thermal Expansion
  • Thermal expansion is used in glass thermometers.
  • As temperature increases, the alcohol (or
    mercury) in the tube expands and its height
    increases.

10
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.

11
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)

12
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13
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

14
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 ? ? ?
15
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.

16
Calorimeter
17
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.

18
Conduction
  • In metals, conduction is faster because some
    electrons are free to move about.

19
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.

20
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.

21
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.

22
Convection
  • Convection currents are important in many natural
    cycles, such as ocean currents, weather systems,
    and movements of hot rock in Earths interior.

23
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.

24
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25
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26
Thermodynamics
  • The study of conversions between thermal energy
    and other forms of energy is called
    thermodynamics.

27
1st Law of Thermodynamics
  • The first law of thermodynamics states that
    energy is conserved.

28
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.)

29
3rd Law of Thermodynamics
  • The third law of thermodynamics states that
    absolute zero cannot be reached.
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