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• Objectives
• Defining Temperature
• Thermal Equilibrium
• Thermal Expansion
• Measuring Temperature
Chapter 9 Section 1 Temperature and
Thermal Equilibrium
Section 1 Temperature and
Thermal Equilibrium Chapter 9
Objectives
• Relate temperature to the kinetic energy of atoms
and molecules.
• Describe the changes in the temperatures of two
objects reaching thermal equilibrium.
• Identify the various temperature scales, and convert
from one scale to another.
Chapter 9
Defining Temperature
• Temperature is a measure of the average kinetic
energy of the particles in a substance.
• Adding or removing energy usually changes
temperature.
• Internal energy is the energy of a substance due to
both the random motions of its particles and to the
potential energy that results from the distances and
alignments between the particles.
Section 1 Temperature and
Thermal Equilibrium
Click below to watch the Visual Concept.
Visual Concepts
Visual Concept
Chapter 9
Forms of Internal Energy
Chapter 9
Thermal Equilibrium
• Thermal equilibrium is the state in which two bodies
in physical contact with each other have identical
temperatures.
– By placing a thermometer in contact with an object and
waiting until the column of liquid in the thermometer stops
rising or falling, you can find the temperature of the object.
– The reason is that the thermometer is in thermal equilibrium
with the object.
• The temperature of any two objects in thermal
equilibrium always lies between their initial
temperatures.
Section 1 Temperature and
Thermal Equilibrium
Click below to watch the Visual Concept.
Visual Concept
Chapter 9
Thermal Equilibrium
Section 1 Temperature and
Thermal Equilibrium
Chapter 9
Thermal Expansion
• In general, if the temperature of a substance
increases, so does its volume. This phenomenon is
known as thermal expansion.
• Different substances undergo different amounts of
expansion for a given temperature change.
• The thermal expansion characteristics of a material
are indicated by a quantity called the coefficient of
volume expansion.
• Gases have the largest values for this coefficient.
Solids typically have the smallest values.
Section 1 Temperature and
Thermal Equilibrium
Click below to watch the Visual Concept.
Visual Concept
Chapter 9
Thermal Expansion
Section 1 Temperature and
Thermal Equilibrium
Chapter 9
Measuring Temperature
• The most common
thermometers use a glass tube
containing a thin column of
mercury, colored alcohol, or
colored mineral spirits.
• When the thermometer is
heated, the volume of the liquid
expands.
• The change in length of the
liquid column is proportional to
the temperature.
Section 1 Temperature and
Thermal Equilibrium
Chapter 9
Measuring Temperature, continued
• When a thermometer is in thermal equilibrium with a mixture of water and ice at one atmosphere of pressure, the temperature is called the ice point or melting point of water. This is defined as zero degrees Celsius, or 0°C.
• When the thermometer is in thermal equilibrium with
a mixture of steam and water at one atmosphere of pressure, the temperature is called the steam point or boiling point of water. This is defined as 100°C.
Section 1 Temperature and
Thermal Equilibrium
Chapter 9
Measuring Temperature, continued
• The temperature scales most widely used today are
the Fahrenheit, Celsius, and Kelvin scales.
• Celsius and Fahrenheit temperature measurements
can be converted to each other using this equation:
Section 1 Temperature and
Thermal Equilibrium
9 32.0
5
9 Fahrenheit temperatu
re
Celsius temperature 32.05
F CT T
• The number 32.0 indicates the difference between
the ice point value in each scale: 0.0ºC and 32.0ºF.
Chapter 9
Measuring Temperature, continued
Section 1 Temperature and
Thermal Equilibrium
• Temperature values in the Celsius and Fahrenheit
scales can have positive, negative, or zero values.
• But because the kinetic energy of the atoms in a
substance must be positive, the absolute
temperature that is proportional to that energy
should be positive also.
• A temperature scale with only positive values is
suggested by the graph on the next slide. This scale
is called the Kelvin scale.
Chapter 9
Measuring Temperature, continued
Section 1 Temperature and
Thermal Equilibrium
• The graph suggests that if
the temperature could be
lowered to –273.15°C, the
pressure would be zero.
• This temperature is
designated in the Kelvin
scale as 0.00 K, where K
represents the
temperature unit called
the kelvin.
• Temperatures in the Kelvin scale are indicated by the
symbol T.
Chapter 9
Measuring Temperature, continued
Section 1 Temperature and
Thermal Equilibrium
• A temperature difference of one degree is the same
on the Celsius and Kelvin scales. The two scales
differ only in the choice of zero point.
• Thus, the ice point (0.00°C) equals 273.15 K, and the
steam point (100.00°C) equals 373.15 K.
• The Celsius temperature can therefore be converted
to the Kelvin temperature by adding 273.15:
T TC 273.15
Kelvin temperature Celsius temperature 273.15
Preview
• Objectives
• Heat and Energy
• Thermal Conduction
• Conservation of Energy
• Sample Problem
Chapter 9 Section 2 Defining Heat
Section 2 Defining Heat Chapter 9
Objectives
• Explain heat as the energy transferred between
substances that are at different temperatures.
• Relate heat and temperature change on the
macroscopic level to particle motion on the
microscopic level.
• Apply the principle of energy conservation to
calculate changes in potential, kinetic, and internal
energy.
Section 2 Defining Heat Chapter 9
Heat and Energy
• Heat is the energy transferred between objects
because of a difference in their temperatures.
• From a macroscopic viewpoint, energy transferred as
heat tends to move from an object at higher
temperature to an object at lower temperature.
• The direction in which energy travels as heat can be
explained at the atomic level, as shown on the next
slide.
Chapter 9
Transfer of Particles’ Kinetic Energy as Heat
Section 2 Defining Heat
Energy is transferred as heat from the higher-energy particles to
the lower-energy particles, as shown on the left. The net energy
transferred is zero when thermal equilibrium is reached, as
shown on the right.
Click below to watch the Visual Concept.
Visual Concept
Chapter 9 Section 2 Defining Heat
Temperature and Heat
Section 2 Defining Heat Chapter 9
Heat and Energy, continued
• The atoms of all objects are in continuous motion, so
all objects have some internal energy.
– Because temperature is a measure of that energy,
all objects have some temperature.
• Heat, on the other hand, is the energy transferred
from one object to another because of the
temperature difference between them.
– When there is no temperature difference
between a substance and its surroundings, no net
energy is transferred as heat.
Section 2 Defining Heat Chapter 9
Heat and Energy, continued
• Just as other forms of energy have a symbol that
identifies them (PE for potential energy, KE for kinetic
energy, U for internal energy, W for work), heat is
indicated by the symbol Q.
• Because heat, like work, is energy in transit, all heat
units can be converted to joules, the SI unit for
energy.
Section 2 Defining Heat Chapter 9
Thermal Conduction
• The type of energy transfer that
is due to atoms transferring
vibrations to neighboring atoms
is called thermal conduction.
• The rate of thermal
conduction depends on the
substance.
• Two other mechanisms for
transferring energy as heat are
convection and
electromagnetic radiation.
When this burner is
turned on, the skillet’s
handle heats up
because of conduction.
Click below to watch the Visual Concept.
Visual Concept
Chapter 9 Section 2 Defining Heat
Convection, Conduction, and Radiation
Section 2 Defining Heat Chapter 9
Conservation of Energy
• If changes in internal energy are taken into account
along with changes in mechanical energy, the total
energy is a universally conserved property.
• In other words, the sum of the changes in
potential, kinetic, and internal energy is equal to
zero.
CONSERVATION OF ENERGY
PE + KE + U = 0
the change in potential energy + the change in kinetic energy
+ the change in internal energy = 0
Click below to watch the Visual Concept.
Visual Concepts
Visual Concept
Chapter 9
Conservation of Energy
Section 2 Defining Heat Chapter 9
Sample Problem
Conservation of Energy
An arrangement similar to the one
used to demonstrate energy
conservation is shown in the figure.
A vessel contains water. Paddles
that are propelled by falling masses
turn in the water. This agitation
warms the water and increases its
internal energy. The temperature of
the water is then measured, giving
an indication of the water’s internal
energy increase.
Section 2 Defining Heat Chapter 9
Sample Problem, continued
Conservation of Energy, continued
If a total mass of 11.5 kg falls 1.3 m
and all of the mechanical energy is
converted to internal energy, by how
much will the internal energy of the
water increase? (Assume no energy
is transferred as heat out of the
vessel to the surroundings or from
the surroundings to the vessel’s
interior.)
Section 2 Defining Heat Chapter 9
Sample Problem, continued
1. Define
Given:
m = 11.5 kg
h = 1.3 m
g = 9.81 m/s2
Unknown:
U = ?
Section 2 Defining Heat Chapter 9
Sample Problem, continued
2. Plan
Choose an equation or situation: Use the conservation of energy, and solve for U.
PE + KE + U = 0
(PEf – PEi) + (KEf – KEi) + U = 0
U = –PEf + PEi – KEf + KEi
Tip: Don’t forget that a change in any quantity, indicated by the symbol ∆, equals the final value minus the initial value.
Section 2 Defining Heat Chapter 9
Sample Problem, continued
Because the masses begin at rest, KEi equals
zero. If we assume that KEf is small compared to
the loss of PE, we can set KEf equal to zero also.
KEf = 0 KEi = 0
Because all of the potential energy is assumed to
be converted to internal energy, PEi can be set
equal to mgh if PEf is set equal to zero.
PEi = mgh PEf = 0
Substitute each quantity into the equation for ∆U:
∆U = –PEf + PEi – KEf + KEi
∆U = 0 + mgh + 0 + 0 = mgh
Section 2 Defining Heat Chapter 9
Sample Problem, continued
4. Evaluate
The answer can be estimated using rounded
values. If m ≈ 10 kg and g ≈ 10 m/s2, then ∆U ≈
130 J, which is close to the actual value calculated.
3. Calculate
Substitute the values into the equation and
solve:
U = mgh
U = (11.5 kg)(9.81 m/s2)(1.3 m)
U = 1.5 102 J
Preview
• Objectives
• Specific Heat Capacity
• Calorimetry
• Sample Problem
• Latent Heat
Chapter 9 Section 3 Changes in
Temperature and Phase
Section 3 Changes in
Temperature and Phase Chapter 9
Objectives
• Perform calculations with specific heat capacity.
• Interpret the various sections of a heating curve.
Section 3 Changes in
Temperature and Phase Chapter 9
Specific Heat Capacity
• The specific heat capacity of a substance is defined
as the energy required to change the temperature of 1
kg of that substance by 1°C.
• Every substance has a unique specific heat capacity.
• This value tells you how much the temperature of a
given mass of that substance will increase or
decrease, based on how much energy is added or
removed as heat.
Section 3 Changes in
Temperature and Phase Chapter 9
Specific Heat Capacity, continued
• Specific heat capacity is expressed mathematically
as follows:
cp Q
mT
specific heat capacity = energy transferred as heat
mass change in temperature
• The subscript p indicates that the specific heat capacity is
measured at constant pressure.
• In this equation, T can be in degrees Celsius or in degrees
Kelvin.
Section 3 Changes in
Temperature and Phase Chapter 9
Calorimetry
• Calorimetry is used
to determine specific
heat capacity.
• Calorimetry is an
experimental
procedure used to
measure the energy
transferred from one
substance to another
as heat.
A simple
calorimeter
allows the
specific
heat
capacity of a
substance to
be
determined.
Click below to watch the Visual Concept.
Visual Concept
Chapter 9 Section 3 Changes in
Temperature and Phase
Calorimetry
Section 3 Changes in
Temperature and Phase Chapter 9
Calorimetry, continued
Because the specific heat capacity of water is well
known (cp,w= 4.186 kJ/kg•°C), the energy transferred as
heat between an object of unknown specific heat
capacity and a known quantity of water can be
measured.
energy absorbed by water = energy released by substance
Qw = –Qx
cp,wmw∆Tw = –cp,xmx∆Tx
Section 3 Changes in
Temperature and Phase Chapter 9
Sample Problem
Calorimetry
A 0.050 kg metal bolt is heated to an unknown initial
temperature. It is then dropped into a calorimeter
containing 0.15 kg of water with an initial temperature
of 21.0°C. The bolt and the water then reach a final
temperature of 25.0°C. If the metal has a specific heat
capacity of 899 J/kg•°C, find the initial temperature of
the metal.
Section 3 Changes in
Temperature and Phase Chapter 9
Sample Problem, continued
1. Define
Given: mm = 0.050 kg cp,m = 899 J/kg•°C
mw = 0.15 kg cp,w = 4186 J/kg•°C
Tw = 21.0°C Tf = 25.0°C
Unknown: Tm = ?
Diagram:
Section 3 Changes in
Temperature and Phase Chapter 9
Sample Problem, continued
2. Plan
Choose an equation or situation: The energy absorbed by the
water equals the energy removed from the bolt.
Qw –Qm
cp,wmwTw –cp,mmmTm
cp,wmw (T f Tw ) –cp,mmm (T f Tm )
Rearrange the equation to isolate the unknown:
Tm cp,wmw(T f Tw )
cp,mmmT f
Section 3 Changes in
Temperature and Phase Chapter 9
Sample Problem, continued
3. Calculate
Substitute the values into the equation and solve:
4. Evaluate
Tm is greater than Tf, as expected.
,
,
(4186 J/kg• C)(0.15 kg)(25.0 C 21.0 C)25.0 C
(899 J/kg C)(0.050 kg)
81 C
( )p w w f w
m f
p m m
m
m
c m T TT T
c m
T
T
Tip: Because Tw is less
than Tf, you know that Tm
must be greater than Tf.
Section 3 Changes in
Temperature and Phase Chapter 9
Latent Heat
• When substances melt, freeze, boil, condense, or
sublime, the energy added or removed changes the
internal energy of the substance without changing the
substance’s temperature.
• These changes in matter are called phase changes.
• The energy per unit mass that is added or removed
during a phase change is called latent heat,
abbreviated as L.
Q = mL
energy transferred as heat during phase change = mass latent heat
Click below to watch the Visual Concept.
Visual Concept
Chapter 9 Section 3 Changes in
Temperature and Phase
Latent Heat
Section 3 Changes in
Temperature and Phase Chapter 9
Latent Heat, continued
• During melting, the energy that is added to a
substance equals the difference between the total
potential energies for particles in the solid and the
liquid phases. This type of latent heat is called the
heat of fusion, abbreviated as Lf.
• During vaporization, the energy that is added to a
substance equals the difference in the potential
energy of attraction between the liquid particles and
between the gas particles. In this case, the latent
heat is called the heat of vaporization, abbreviated
as Lv.
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