Transcript Chapter 16 Power Point Notes

Chapter 16
Thermal Energy and Heat
16.1 Thermal
Energy and Matter
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.
Temperature
Temperature is related to the
average kinetic energy of the
particles in an object due to
their random motions
through space.
Temperature
Temperature is a measure of how hot or
cold an object is compared to a reference
point.
• On the Celsius scale, the reference
points are the freezing and boiling
points of water.
• On the Kelvin scale, absolute zero is
defined as a temperature of 0 kelvins.
Thermal Energy
Thermal energy is related to 2
variables:
Thermal energy is the total
potential and kinetic energy of
all the particles in an object.
It depends on the mass,
temperature, and phase (solid,
liquid, or gas) of an object.
Thermal Contraction and Expansion
Thermal expansion is an
increase in the volume of a
material due to a temperature
increase.
It occurs when particles of
matter move farther apart as
temperature increases.
Specific Heat
Specific heat is the amount of heat
needed to raise the temperature of
one gram of a material by one
degree Celsius.
The lower a material’s specific heat, the
more its temperature rises when a given
amount of energy is absorbed by a given
mass.
Specific Heat
In this formula, heat is in joules,
mass is in grams, specific heat is
in J/g•°C, and the temperature
change is in degrees Celsius.
Specific Heat
Calculating Specific Heat
An iron skillet has a mass of
500.0 grams. The specific
heat of iron is 0.449 J/g•°C.
How much heat must be
absorbed to raise the
skillet’s temperature by
95.0°C?
Specific Heat
Calculating Specific Heat
Mass of iron m = 500g
Specific heat c=20449J/g∙°C
Change in temp ΔT = 95 °C
Q = 500 x .449 x 95
Q = 21,375 J = 21.4 kJ
Specific Heat
A calorimeter is an
instrument used to measure
changes in thermal energy.
The lower a material’s specific heat,
the more its temperature rises when
a given amount of energy is
absorbed by a given mass.
Specific Heat
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.
The calorimeter is sealed to
prevent thermal energy from
escaping.
Specific Heat
A calorimeter is
used to measure
specific heat. A
sample is heated
and placed in the
calorimeter. The
temperature
change is
observed.
Assessment Questions
1.
What is the thermal energy of an object?
a. the total number of atoms or molecules
b. the total kinetic energy of the atoms or
molecules
c. the average kinetic energy of the atoms
or molecules
d. the average mechanical energy of the
atoms or molecules
Assessment Questions
1.
What is the thermal energy of an object?
a. the total number of atoms or molecules
b. the total kinetic energy of the atoms or
molecules
c. the average kinetic energy of the atoms
or molecules
d. the average mechanical energy of the
atoms or molecules
Assessment Questions
2. What causes a gas to expand when its
temperature is increased?
a. The number of particles increases as
temperature increases.
b. Each particle expands as its temperature
increases, so the total volume increases.
c. As temperature increases, more electrons
leave atoms and move separately.
d. As gas particles move faster, they
overcome some forces of attraction.
Assessment Questions
2. What causes a gas to expand when its
temperature is increased?
a. The number of particles increases as
temperature increases.
b. Each particle expands as its temperature
increases, so the total volume increases.
c. As temperature increases, more electrons
leave atoms and move separately.
d. As gas particles move faster, they
overcome some forces of attraction.
Assessment Questions
3. The specific heat of water is 4.18
J/g•°C. How much heat is
required to raise the temperature
of 1,000 grams of water by 50°C?
a.83.6 J
b.83.6 kJ
c. 209 J
d.209 kJ
Assessment Questions
3. The specific heat of water is 4.18
J/g•°C. How much heat is
required to raise the temperature
of 1,000 grams of water by 50°C?
a.83.6 J
b.83.6 kJ
c. 209 J
d.209 kJ
Assessment Questions
4. What property of matter can be
measured using a calorimeter?
a.temperature
b.thermal expansion
c. specific heat
d.mass
Assessment Questions
4. What property of matter can be
measured using a calorimeter?
a.temperature
b.thermal expansion
c. specific heat
d.mass
Assessment Questions
5. Temperature is the transfer of
thermal energy from one object to
another.
True
False
Chapter 16
Thermal Energy and Heat
16.2 Heat and
Thermodynamics
Conduction
Conduction is the transfer of
thermal energy with no overall
transfer of matter.
Conduction in gases is slower
than in liquids and solids
because the particles in a gas
collide less often.
Conduction
Conduction occurs within a
material or between materials
that are touching.
In conduction, collisions
between particles transfer
thermal energy, without any
overall transfer of matter.
Conduction
Thermal Conductors
A thermal conductor is a
material that conducts
thermal energy well.
Conduction
Thermal Insulators
A material that conducts
thermal energy poorly is called
a thermal insulator.
Convection
Convection is the transfer of
thermal energy when particles of
a fluid move from one place to
another.
Convection currents are important in many
natural cycles, such as ocean currents,
weather systems, and movements of hot
rock in Earth’s interior.
Convection
A convection current occurs when a
fluid circulates in a loop as it
alternately heats up and cools down.
• Air at the bottom of an oven heats up,
expands, and becomes less dense. The
hot air rises.
• Rising hot air cools as it moves away
from the heat source.
• As a result, the coolest air is at the top
of the oven.
Radiation
Radiation 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.
Heat Transfer Question
 Identify
the method of heat
transfer in the following: an egg
cooking in a frying pan; a warm
air mass bringing a change in
weather; the wire of an electric
appliance becoming hot; heat
from a fireplace warming a room
Thermodynamics
The study of
conversions between
thermal energy and
other forms of energy
is called
thermodynamics.
Thermodynamics
First Law of Thermodynamics
The first law of
thermodynamics states
that energy is
conserved.
Thermodynamics
Second 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.
Thermodynamics
A heat engine is any device that
converts heat into work.
• The efficiency of a heat engine is
always less than 100 percent.
• Thermal energy that is not
converted into work is called
waste heat.
• Waste heat is lost to the
surrounding environment.
Thermodynamics
Spontaneous changes will always
make a system less orderly,
unless work is done on the
system.
Thermodynamics
Third Law of Thermodynamics
The third law of
thermodynamics states
that absolute zero cannot
be reached.
Assessment Questions
1.
What form of energy transfer
requires the motion of particles of
a fluid?
a.conduction
b.convection
c. radiation
d.insulation
Assessment Questions
1.
What form of energy transfer
requires the motion of particles of
a fluid?
a.conduction
b.convection
c. radiation
d.insulation
Assessment Questions
2.
What happens in every case in
which energy is added to a
system?
a.Temperature increases.
b.Work is done on the system.
c. All of the energy can be
accounted for as work or heat.
d.An identical amount of energy is
removed from the system.
Assessment Questions
2.
What happens in every case in
which energy is added to a
system?
a.Temperature increases.
b.Work is done on the system.
c. All of the energy can be
accounted for as work or heat.
d.An identical amount of energy is
removed from the system.
Assessment Questions
3.
Thermal energy can move from a
cooler object to a warmer object when
a. the warmer object is larger.
b. the cooler object has more thermal
energy.
c. energy is transferred by radiation.
d. work is done on the system.
Assessment Questions
3.
Thermal energy can move from a
cooler object to a warmer object when
a. the warmer object is larger.
b. the cooler object has more thermal
energy.
c. energy is transferred by radiation.
d. work is done on the system.
Assessment Questions
4.
According to the third law of
thermodynamics, it is impossible
a. to cool an object to absolute zero.
b. transfer thermal energy from a
cooler object to a warmer object.
c. convert energy from one form to
another.
d. account for all of the energy in a
system.
Assessment Questions
4.
According to the third law of
thermodynamics, it is impossible
a. to cool an object to absolute zero.
b. transfer thermal energy from a
cooler object to a warmer object.
c. convert energy from one form to
another.
d. account for all of the energy in a
system.
Assessment Questions
5. All metals are good thermal
insulators.
True
False
Assessment Questions
5. All metals are good thermal
insulators.
True
False