Transcript Chapter 16 – Thermal Energy and Heat

Chapter 16 – Thermal
Energy and Heat
Section 16.1 – Thermal Energy and
Matter

In the 1700’s most scientists thought that
heat was a fluid called caloric that flowed
between objects.
Count Rumford
Rumford 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.

Work and Heat
Some 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.

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.

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.

Thermal Contraction
Slower particles collide less often and
exert less force, so pressure decreases
and the object contracts.
 This is called thermal contraction.

Thermal Expansion
Thermal 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.

Thermal Expansion
Thermal expansion is used in glass
thermometers.
 As temperature increases, the alcohol (or
mercury) in the tube expands and its
height increases.

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 material’s specific heat, the
more its temperature rises when a given
amount of energy is absorbed by a given
mass.

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)
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
skillet’s 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) = 21,375J

Practice Problems
How much heat is needed to raise the
temperature of 100.0g of water by
85.0oC?
Q = (100.0g)(4.18J/goC)(85.0oC) = 35,530J


How much heat in kJ is absorbed by a
750g iron skillet when its temperature
rises from 25oC to 125oC?
DT = 125oC – 25oC = 100oC
Q = (750g)(0.449J/goC)(100oC) = 33,675J
K h d u d c m
33,675J = 33.7kJ

Practice Problems

In setting up an aquarium, the heater
transfers 1200kJ of heat to 75,000g of
water. What is the increase in the water’s
temperature?
Q = m x c x DT DT = Q/(m x c) 1200kJ = 1,200,000J
DT = 1,200,000J/(75,000g x 4.18J/goC) = 3.8oC

What mass of water will change its
temperature by 3.0oC when 525J of heat
is added to it?
Q = m x c x DT
m = Q/(c x DT)
m = 525J/(4.18J/goC x 3.0oC) = 41.9g
Section 16.1 Section Assessment
In 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?

Section 16.1 Section Assessment
How 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?

Section 16.1 Section Assessment
The 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 45.0oC?
DT = 45oC – 25oC = 20oC
Q = (1000.0g)(0.39J/goC)(20oC) = 7800J

A peanut burned in a calorimeter transfers
18,200J to 100.0g of water. What is the
rise in the water’s temperature?
Q = m x c x DT DT = Q/(m x c)
DT = 18,200J/(100.0g x 4.18J/goC) = 43.5oC

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.

Conduction

In metals, conduction is faster because
some electrons are free to move about.
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.

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.

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.

Convection

Convection currents are important in many
natural cycles, such as ocean currents,
weather systems, and movements of hot
rock in Earth’s interior.
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.

Thermodynamics

The study of conversions between thermal
energy and other forms of energy is called
thermodynamics.
st
1

Law of Thermodynamics
The first law of thermodynamics states
that energy is conserved.
nd
2

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.)
rd
3

Law of Thermodynamics
The third law of thermodynamics states
that absolute zero cannot be reached.
Section 16.2 Section Assessment
Why 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.

Section 16.2 Section Assessment
What 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.
