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Title: Chapter 9 Heat

1
Chapter 9 Heat
• Pages 297 320
• Coach Kelsoe

2
Chapter 9 Heat
• Section One
• Temperature and Thermal Equilibrium
• Pages 298 - 304

3
Section One 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

4
Section One Vocabulary
• Temperature a measure of the average kinetic
energy of the particles in a substance
• Internal energy 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
• Thermal equilibrium the state in which two
bodies in physical contact with each other have
identical temperatures

5
Section One Formulas
• Celsius Fahrenheit Temperature Conversion
• Fahrenheit temperature (9/5 x Celsius
temperature) 32.0
• Celsius Kelvin Temperature Conversion
• T TC 273.15

6
Temperature Thermal Equilibrium
• The temperature of a substance is proportional to
the average kinetic energy of particles in the
substance.
• A substances temperature increases as a direct
result of added energy being distributed among
the particles of the substance.
• The energies associated with atomic motion are
referred to as internal energy, which is
proportional to the substances temperature.

7
Temperature Thermal Equilibrium
• Thermal equilibrium is the basis for measuring
temperature with thermometers.
• 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.
• Remember that thermal equilibrium is the state in
which two bodies in physical contact with each
other have identical temperatures.

8
Practice Problem
• What is the equivalent Celsius temperature of
50.0F?
• Given TF 50.0F
• Unknown TC ?
• Use the Celsius-Fahrenheit equation to convert
Fahrenheit into Celsius.
• TF 9/5TC 32.0
• TC 5/9 (TF 32.0)
• TC 5/9 (50.0 32.0)C 10.0C

9
Practice Problem
• What is the equivalent Kelvin temperature of
50.0F?
• Use the Celsius-Kelvin equation to convert
Celsius into Kelvin.
• T TC 273.15
• T (10.0 273.15)K 283.2 K

10
Chapter 9 Heat
• Section Two
• Defining Heat
• Pages 305 - 312

11
Section Two 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

12
Section Two Vocabulary
• Heat the energy transferred between objects
because of a difference in their temperatures

13
Section Two Formula
• Conservation of Energy
• ?PE ?KE ?U 0

14
Defining Heat
• Heat is the energy transferred between objects
because of a difference in their temperatures.
• The word heat is sometimes used to refer to the
process by which energy is transferred between
objects because of a difference in their
temperatures.

15
Heat
• Heat- the energy transferred between objects
because of a difference in their temperatures
• Energy is transferred between substances as heat.
• The symbol for heat is Q and is measured in
joules (J).

16
Internal Energy
• When objects collide inelastically, not all of
their initial kinetic energy remains as kinetic
energy after the collision. Some of the energy is
absorbed as internal energy by the objects.
• Ex. If you pull out a nail after hammering it
into wood, it feels warm. The nail encounters
friction as it is pulled out the energy required
to overcome the friction is transformed into
internal energy. The increased internal energy
raises the nails temperature.
• The symbol for a change in internal energy is ?U.

17
Conservation of Energy
• ?PE ?KE ?U 0 (change in potential energy
change in kinetic energy change in internal
energy 0)

18
Specific Heat Capacity
• 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.
• c(p) Q/m?T (specific heat capacity energy
transferred as heat / mass change in
temperature)

19
Calorimetry
• Calorimetry is used to determine specific heat
capacity.
• To measure the specific heat capacity of a
substance you must measure the mass, temperature
change, and energy transferred as heat.
• You can find the mass and ?T directly, but to
find the measurement of heat you have to measure
the heat transferred between the object and a
known quantity of water.
• cp,wmw?Tw -cp,xmx?Tx (Specific heat
capacity of water mass of water change of
temperature of water - Specific heat capacity
of substance mass of substance change of
temperature of substance)

20
Latent Heat
• When substances melt, freeze, boil, or condense,
the energy added or removed changes the internal
energy without changing the substances
temperature. These changes are called phase
changes.
• Latent heat is energy transferred during phase
changes.

21
Practice Problem
• A 61.4 kg roller skater on level ground brakes
from 20.5 m/s to 0 m/s. What is the total change
in the internal energy of the system?
• Given m61.4 kg
• vi20.5 m/s vf0 m/s
• Find potential and kinetic energy using the
givens.

22
Practice Problem
• There is no potential energy since the roller
skater is in motion.
• To find kinetic energy use the formula
• KE ½mv2
• Kinetic energy 12,870.98 J
• ?PE ?KE ?U 0
• 0 12,870.98J ?U 0
• ?U -12,870.98J

23
The First Law of Thermodynamics!
24
Symbols to Know
• Quantities
Units
• U change in internal energy
J joules
• Q heat
J joules
• W work
J joules
• eff efficiency
(unit less)

25
Positive or Negative?
• Sign Convention for heat, q
• Heat is transferred into the system ? q gt 0
• Heat is transferred out of the system ? q lt 0
• Sign Convention for work, w
• Work is done upon the system by the surroundings
? w lt 0
• Work is done by the system on the surroundings ?
w gt 0

26
UQ-W Change in systems internal energyenergy
transferred to or from system as heat-energy
transferred to or from as work
• The principle of energy conservation that takes
into account a systems internal energy as well
as work and heat is called the first law of
thermodynamics.

27
Sample Problem
• A total of 135J of work is done on a gaseous
refrigerant as it undergoes compression. If the
internal energy of the gas increases by 114J
during the process, what is the total amount of
energy transferred as heat? Has energy been
added to or removed from the refrigerant as heat?

28
Sample Problem
• Given W -135J U 114J
• Unknown Q ?
• (since the work is done on the gas, W is a
negative value)
• First rearrange the equation UQ-W to Q
UW
• Now plug in the values
• Q114J(-135J)
• Q -21J (sign for Q is negative, which indicates
energy is transferred as heat from the
refrigerant)

29
The Second Law of Thermodynamics!!
30
The Basis for the Law
• The requirement that a heat engine give up some
energy at a lower temperature in order to do work
does not follow the first law.
• Therefore this requirement is the basis of what
is called the second law of thermodynamics.
• The second law states that no machine can
transfer all of its absorbed energy as work.

31
When you shuffle a deck of cards, it is highly
improbable that the cards would end up separated
by suit and in numerical sequence.
Example
• Such a highly ordered arrangement can be formed
in only a few ways, but there are more than 8 x
1067 ways to arrange 52 cards.

32
Definition
• A measure of the randomness or disorder of a
system

The greater the entropy of a system is, the
greater a systems disorder!!!!
33
• Once a system has reached a state of greatest
disorder, it will tend to remain in that state
and have maximum entropy.

34
• A small decrease in entropy more order or less
disorder
• A large increase in entropy less order or more
disorder

35
DID YOU KNOW?
• Entropy decreases in many systems on Earth. For
example, atoms and molecules become incorporated
into complex and orderly biological structures
such as cells and tissues. These appear to be
spontaneous because we think of the Earth itself
as a closed system. So much energy comes from the
sun that the disorder in chemical and biological
systems is reduced, while the total entropy of
the Earth, sun, and intervening space increases.

36
The entropy of the universe increases in all
natural processes.