THERMAL ENERGY AND HEAT

1
THERMAL ENERGY AND HEAT
Temperature and thermal energy The nature of
heat States of Matter Uses of Heat
MRS. SHARPLESS - TEAM E MR. CONRAD - TEAM F
2
When scientists think about the temperature of
something, they consider the atoms and molecules
that make up that thing.
TEMPERATURE - the measure of the average kinetic
energy of atoms/molecules in an object.
These atoms and molecules are always moving, even
if the object they make up is not moving!! This
means that the atoms/molecules have kinetic
energy, or energy of MOTION.
3
Temperature

• Think about a day during each season where you
  live.
• Write down an adjective that describes the
  temperature for each day.
• Did you use adjectives or numbers to describe the
  temperature?
• What advantage does using numbers have?

4
Temperature Scales
There are 3 scales that are commonly used
throughout the world.
1. Fahrenheit scale - Most commonly used scale
in the US. Water freezes at 32 degrees, and
water boils at 212 degrees. There are 180
degrees between freezing and boiling.
5
More Temperature scales
2. Celsius scale - The temperature scale used
throughout the world. Water freezes at 0
degrees, and water boils at 100 degrees. There
are 100 degrees between the boiling and freezing
points on this scale.
6
More Temperature Scales
3. Kelvin scale - This scale is used mostly by
scientists to measure temperature extremes. The
freezing point of water is 273 K and the boiling
point of water is 373 K.
If 273 K freezes water, how cold do you think
zero degrees K would be?
7
Temperature
Temperature Scales
Scale Freezing Point Boiling Point
Fahrenheit Celsius Kelvin
32º 212º 0º 100º 273º 373º
8
Zero degrees Kelvin, or -273 degrees Celsius.
The lowest possible temperature you can possibly
have. The atoms in a substance at this
temperature would stop moving!!
Absolute Zero -
9
Temperature
10
The total energy of all the particles (atoms,
molecules) in a substance. High temp more
energy, low temp less energy.
THERMAL ENERGY -
The movement of thermal energy from a substance
at a higher temperature to a substance at a lower
temperature.
HEAT -
11
THERE ARE 3 WAYS THAT HEAT CAN MOVE.
Heat is transferred from one atom to the next
atom inside an object. (Usually a solid)
Conduction -
If you held on to a metal rod on one end, and put
the other end into a fire, what would eventually
happen to you?
12
Heat is transferred by the movement of currents
in a fluid (a liquid or gas)
Convection -
The heated gas or liquid rises (less dense), and
the cooler gas or liquid sinks (more dense).
This rising of heated air/liquid and falling of
cooled air/liquid cycles in a circular motion
called a convection current.
Convection currents are used to heat homes, and
can also be found in nature.
13
Radiation -
The transfer of heat energy through empty space
by waves.
An example of radiation would be if you were
standing close to a campfire. You receive the
heat energy from the nearby fire even though you
are not in contact with it. The Sun transfers
heat energy by this method.
14
If you have two objects at different
temperatures, which direction will the heat
energy move? From Hot to Cold object or Cold to
Hot object?
Heat Flow
Heat always moves from a hot area/object to a
colder area/object. Heat will flow from one
substance to another until the temperatures
(thermal energy) of BOTH objects is the same.
15
Materials that allow heat energy to pass through
them easily. A good example would be most metals.
Conductors -
Materials that do not allow heat energy to pass
through them very easily. Examples would be
plastics, wood, and fiberglass.
Insulators -
16
Specific Heat
The amount of energy required to raise the
temperature of one kilogram of a substance by one
degree Kelvin. Measured in Joules per
kilogram/kelvin or J/(kg K).
ALUMINUM - 90.3 J/(KgK) BRASS - 376
J/(KgK) COPPER - 385 J/(KgK) WATER - 4,180
J/(KgK)
17
Specific Heat
How much heat is required to raise the
temperature of 5 kilograms of water 10 Kelvins?
FORMULA Change in energy Mass X Specific Heat
X Change in Temperature
Change in energy (5kg) X (4,180 J/kgK) X (10K)
209,000 J
18
The 3 States of Matter
Matter exists in 3 states. SOLIDS, LIQUIDS,
GASES. The chemical makeup of the substance in
all three states is the same. HOWEVER, the
spaces between atoms that make up the substance
change from one state to another.
SOLIDS
LIQUIDS
GASES
19
A physical change from one state of matter to
another. This can occur between the solid and
liquid state or the liquid and gas state.
Change of State -
As you add more, or take away thermal energy,
matter will change from one state to another.
20
Melting -
The change of state from solid to liquid. The
atoms that make up the solid gain thermal energy
and move apart.
Melting point -
The temperature at which a solid changes to a
liquid. The melting point is different for
different substances.
21
The change of state from a liquid to a solid.
The liquid loses thermal energy, and the atoms of
the substance come close together.
Freezing -
Freezing point -
The temperature at which a substance changes from
a liquid to a solid.
22
Vaporization -
The process by which matter changes from the
liquid to the gas state. Atoms in a substance
gain more thermal energy and separate further
from each other.
23
Vaporization can occur on the surface, or below
the surface of a liquid.
Vaporization that occurs on the surface of a
liquid. Atoms escape from the surface.
Evaporation -
Vaporization that occurs below the surface of a
liquid at higher temperatures.
Boiling -
The temperature at which a liquid boils. The
boiling point is different from one substance to
another.
Boiling point -
24
Condensation
The state change where a gas turns into a liquid.
The atoms which make up the gas lose thermal
energy, and draw closer together.
Think about how a soda can or bottle sweats on
a hot summer day - CONDENSATION!
25
Thermal Expansion
As the thermal energy (temperature)of a substance
increases, its particles spread out and the
substance expands. What happens to the particles
in the substance when the thermal energy
decreases (temperature goes down)?
Thermal expansion - The expanding of matter when
it is heated.
26
Heat-regulating devices. Many of these contain
bimetallic strips, which are strips of two
different metals joined together.
Thermostats -
When the bimetallic strip is heated, one metal
expands faster than the other. The strip bends
into a curve, and triggers a switch to turn
on/off the heat/furnace.
27
Use the process of combustion - the process of
burning a fuel (chemical energy) to produce
thermal (Heat) energy. Heat engines - convert
thermal energy to mechanical energy (energy of
motion).
Heat Engines -
28
Types of Combustion Engines
External Combustion Engine - The fuel is burned
OUTSIDE the engine. Steam engines are an example
of this. Fuel is burned to produce steam, then
the steam is put into the engine to run it.
29
Types of Combustion Engines
Internal Combustion Engine - The fuel is burned
INSIDE the engine in compartments called
cylinders. Gasoline and diesel car engines are
examples of these. Pistons inside the cylinders
move to produce mechanical energy (motion).
30
A device that uses an outside energy source
(electrical energy) to transfer thermal energy
from a cool area to a warm area.
Refrigerators -