Chapter 5: Temperature and Thermal Energy

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Chapter 5 Temperature and Thermal Energy
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Temperature a measure of the average Kinetic
Energy of the particles contained in an object.
Thermal Expansion the process by which materials
expand in volume as their particles gain KE from
heat and move faster. Extra KE weakens the
bonds between particles allowing them to pull
further apart increasing their volume.
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Temperature Scales Fahrenheit Thermometer
A mercury thermometer developed by Gabriel
Fahrenheit in 1714. He used the highest and
lowest outdoor temperatures in his native Germany
as 1000 and 00. Water froze at 320 on his
thermometer
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Temperature Scales
Celsius Thermometer
In 1742, Anders Celsius, a Swedish astronomer
wanted to develop a scientific/metric based
thermometer using easily measurable quantities.
He choose 00 as the freezing point of water and
1000 as the boiling point of water.
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Temperature Scales
Kelvin Thermometer
A scale developed by William Thompson, Lord
Kelvin, a famous English physicist in the mid
1800s.
This scale was to be a scientific temperature
scale with 00 as the lowest possible
temperature (absolute zero).
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Comparison of Temperature scales
Waterboils
212
100
373
Water Freezes
273
32
0
Fahrenheit
Celsius
Kelvin
Abs. zero
-459
-273
0
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Absolute Zero the lowest possible temperature
for matter is found to be about 273.15 0C.
(-459 0F) At this temperature all particle
motion in a substance will stop (KE 0).
This temperature has never been reached in the
laboratory although scientists have gotten very
close.
Kelvin Temp Celsius temp 273 degrees
Celsius Temp. Kelvin Temp 270 degrees
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Celsius and Fahrenheit
The relationship between F and C is more
complicated due to the different sizes of the
degrees and the 32 degree offset for the freezing
point of water. The Fahrenheit degree is on
0.56 the size of a Celsius degree,
F 1.8 C 32
C ( F 32 ) x 0.56
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Thermal Expansion the process by which most
materials expand in volume, as its particles
absorb KE and move faster.
Extra KE weakens the bonds (forces) that
hold a substance together allowing the particles
to pull further apart and thereby increasing the
volume of the substance. This happens in all
substances.
Examples of Thermal Expansion Ø     a bar of
metal getting longer when its heated, Ø     a
concrete roadway buckling on a hot summer day.
Ø     Liquid rising inside a thermometer.
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Thermal Energy Video
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Thermal Energy the name given to energy in the
form of heat.
Ø     the total energy, kinetic and potential
possessed by the particles that make up any
material. Ø     Thermal energy, like all types
of energy, is measured in Joules. Heat is
thermal energy in motion. Ø     Thermal energy
that flows from a hotter substance to a colder
substance. Ø     We measure heat by determining
the amount of thermal energy that flows
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Specific Heat Capacity C the quantity of heat
required to raise the temperature of a unit mass
(1 gram or 1 kg) of a substance by 1 degree
Celsius.
Different substances have different capacities
for storing thermal energy. Ø     Metals
generally need less energy to raise their
temperatures by 1 degree C. Ø     Liquids
generally need more heat to raise their
temperatures by 1 degree C. For water 4186
J of energy are required to raise the
temperature of 1 kilogram of water by 1 0C.
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Calculating the Heat gained or lost.
TE m C ?T Where m is the mass of a
substance in kilograms C is the specific
heat capacity ?T is the temperature
difference in 0C ?T Thot -
Tcold
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Mechanisms of Heat Transfer
Conduction the flow of heat by direct contact
between two substances.
Heat moves between the stove and the teapot by
conduction. Conduction also occurs between the
bottom of the glass and molecules of water in
contact with the bottom.
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Conductor materials that conduct heat. Metals
are good conductors because heat is easily
transferred through the atoms making up the metal.
Insulator a material whose internal arrangement
of atoms makes the transfer of heat difficult.
Liquids and gases are generally good
insulators because the bonds connecting particles
are weaker and dont readily transmit energy.
Examples of good insulators as are plastics,
spun fiber glass and wood. Trapped air is often
used as an insulator in clothing, home insulation
etc.
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Mechanisms of Heat transfer
Convection involves the transfer of heat by
bulk movement of particles. Convection occurs
most often in fluids liquids and gases but can
under certain circumstances occur in solids like
the rock in the interior of the earth.
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Mechanisms of Heat transfer
Radiation the transfer of heat energy by
electromagnetic radiation. Energy in the form of
electromagnetic waves that can travel through
air, water, and empty space. Substantial
amounts of radiation reach the Earth every second
in the form of visible light and Infrared
radiation (heat energy)
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Heat transfer in an automobile engine
Convection Water carries heat to radiator
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• About 40, of the heat released by the explosive
  burning of the fuel-air mixture does work driving
  the piston downward and rotating the crankshaft.
• The other 60 of the heat must be removed to
  avoid overheating the engine as follows
• Hot gasses exit the exhaust valve and travel
  through the exhaust pipes to the outside air.
• Conduction moves heat through the cylinder
  wall and into the cooling water which is pumped
  through hoses to the radiator and finally to
  the outside air.

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Heating systems systems that convert chemical
energy from fuels like coal, gas, and oil into
thermal energy that is used to head living
spaces. Convection transfers heat into living
spaces by moving warm air, steam or hot water.
Air then moves that heat around the room. Some of
the thermal energy produced in the heater must be
discharged into the atmosphere up a chimney and
is lost. Electrical heating systems transfer
electrical energy into heat. Insulation is one
way of minimizing the amounts of energy that are
lost to the atmosphere.
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Heating Systems.
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Cooling System any device or process that uses
mechanical energy to transfer thermal energy from
interior living spaces to the outside.
Examples are refrigerators, air conditioners,
freezers. Most systems use a motor to convert
electrical energy into mechanical energy.
Through the use of several physical processes,
thermal energy can be moved from a cooler area to
a normally warmer area like the outside on a hot
day.
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Kinetic Theory of Matter
Ø     All matter is made up of
particles either atoms
or molecules Ø     particles are in
constant motion (Kinetic energy) Ø     The
amount of motion determines the strength of the
electrical forces between the atoms of the
substance. Ø     The strength of the electrical
forces determines the phase of the substance
solid, liquid, or gas.
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Solids have a definite shape, as the particles
are bound tightly together and a definite
volume. If the amount of particle KE is higher
that than in a solid, the bonds are strained and
cannot hold particles together as tightly.
Particles are still bound together but can more
around each other.

• Crystalline solids regular geometric
  arrangements of atoms bound together by
  electrical forces. Example quartz crystal,
  sulfur crystal

• Amorphous solids no regular pattern to the
  atoms. Example glass

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Liquids are phases of matter with higher KE
allowing particles to flow past each
Liquids flow allows them to take the shape of
their container so liquids have an Indefinite
shape. Liquid volumes will not change under
ordinary conditions giving liquids a Definite
volume Liquid volumes increase as you add heat.
Heat adds extra KE that further weakens the
bonds allowing the particles to move further
apart.
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Gases exist as the phase of matter with even
higher KEs. The bonds between particles in gses
are completely broken so each particle exists
independently gases have an indefinite volume
and an indefinite shape, since they completely
fill any container.
Plasmas are gases with extremely high KEs. At
these energy levels, electrons are stripped away
from the atoms leaving the atoms with overall
positive charges mingling with the free
negatively charged electrons. Therefore a plasma
is a hot, electrical conductive gas.