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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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