Section 161 Thermal Energy and Matter In the 1700s most scientists thought that heat was a fluid called caloric that flowed between objects Count Rumford Rumford studied the process of ID: 747927
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Slide1
Chapter 16 – Thermal Energy and HeatSlide2
Section 16.1 – Thermal Energy and MatterIn the 1700’s most scientists thought that heat was a fluid called caloric
that flowed between objects.Slide3
Count RumfordRumford studied the process of drilling holes in the barrels of cannons.
The process occurred in
water
so that the
metal
would not
melt due to the heat produced.Rumford discovered that the heat was a result of the motion of the drill, not a form of matter.Slide4
Work and HeatSome of the work done by the drill does useful work, but some energy is lost due to friction
.
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.Slide5
TemperatureTemperature 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.Slide6
Thermal EnergyThermal 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
.Slide7
Thermal ContractionSlower particles collide less often and exert less force, so pressure decreases and the object contracts.This is called
thermal contraction
.Slide8
Thermal ExpansionThermal expansion is an increase in the volume of a material due to a temperature increase.Thermal expansion occurs when particles of matter move farther
apart as temperature
increases
.
Gases
expand more than
liquids and liquids usually expand more than solids.Slide9
Thermal ExpansionThermal expansion is used in glass thermometers.As temperature increases, the alcohol (or mercury) in the tube expands and its height increases.Slide10
Specific HeatSpecific heat is the amount of heat needed to rise the temperature of one gram of a material by one degree Celsius.The
lower
the material’s specific heat, the more its temperature
rises
when a given amount of energy is absorbed by a given mass.Slide11
Specific HeatFormula for Specific heat: Q = m x c x
D
T
Q = heat (J)
m = mass (g)
c = specific heat (J/g
oC) D
T = change in temperature final – initial (
o
C) Slide12
Sample ProblemAn 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 skillet’s temperature by 95.0oC?
Q = m x c x
D
T
m = 500.0 g
c = 0.449 J/go
C
D
T = 95.0
o
C
Q = (500.0g)(0.449 J/g
o
C)(95.0
o
C) = 21,375J
Slide13
Practice ProblemsHow 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 25
o
C to 125
o
C?
Q = (100.0g)(4.18J/g
o
C)(
85.0
o
C) = 35,530J
D
T = 125
o
C – 25
o
C = 100
o
C
Q = (750g)(0.449J/g
o
C)(100
o
C) = 33,675J
K
h d
u
d c m 33,675J = 33.7kJ
Slide14
Practice ProblemsIn setting up an aquarium, the heater transfers 1200kJ of heat to 75,000g of water. What is the increase in the water’s temperature?
What mass of water will change its temperature by 3.0
o
C when 525J of heat is added to it?
Q = m x c x
D
T
D
T = Q/(m x c) 1200kJ = 1,200,000J
D
T = 1,200,000J/(75,000g x 4.18J/g
o
C) = 3.8
o
C
Q = m x c x
D
T m = Q/(c x
D
T)
m = 525J/(4.18J/g
o
C x 3.0
o
C) = 41.9gSlide15
Section 16.1 Section AssessmentIn what direction does heat flow on its own spontaneously?How is the temperature of an object related to the average kinetic energy of its particles?Name two variables that affect the thermal energy of an object.
What causes thermal expansion of an object when it is heated?Slide16
Section 16.1 Section AssessmentHow do the temperature increases of different materials depend on their specific heats?What principle explains how a calorimeter is used to measure the specific heat of a sample material?Why is it necessary to have regularly spaced gaps between sections of a concrete sidewalk?Slide17
Section 16.1 Section AssessmentThe specific heat of copper is 0.39J/goC. How much heat is needed to raise the temperature of 1000.0g of copper from 25.0oC to 45.0
o
C?
A peanut burned in a calorimeter transfers 18,200J to 100.0g of water. What is the rise in the water’s temperature?
D
T = 45
o
C – 25
o
C = 20
o
C
Q = (1000.0g)(0.39J/g
o
C)(20
o
C) = 7800J
Q = m x c x
D
T
D
T = Q/(m x c)
D
T = 18,200J/(100.0g x 4.18J/g
o
C) = 43.5
o
CSlide18
Section 16.2 – Heat and ThermodynamicsConduction 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.Slide19
ConductionIn metals, conduction is faster because some electrons are free to move about.Slide20
ConductorsA 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. Slide21
InsulatorsA 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. Slide22
ConvectionConvection 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.Slide23
ConvectionConvection currents are important in many natural cycles, such as ocean currents, weather systems, and movements of hot rock in Earth’s interior.Slide24
RadiationRadiation is the transfer of energy by waves moving through space. All objects radiate energy. As an object’s temperature
increases
, the rate at which it radiates energy
increases.Slide25Slide26Slide27
ThermodynamicsThe study of conversions between thermal energy and other forms of energy is called thermodynamics.Slide28
1st Law of ThermodynamicsThe first law of thermodynamics states that energy is conserved.Slide29
2nd Law of ThermodynamicsThe 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
.)Slide30
3rd Law of ThermodynamicsThe third law of thermodynamics states that absolute zero cannot be reached.Slide31
Section 16.2 Section AssessmentWhy is conduction in gases slower than conduction in liquids or solids?Give three examples of convection currents that occur in natural cycles.What happens to radiation from an object as its temperature increases?State the first law of thermodynamics.Slide32
Section 16.2 Section AssessmentWhat is the second law of thermodynamics?State the third law of thermodynamics.If you bedroom is cold, you might feel warmer with several thin blankets than one thick one. Explain why.