Heating up the
classroom with
Thermal
Energy
• Measure of kinetic
energy of molecules
• Thermometer
• Fahrenheit
• Celsius
• Kelvin
On the Kelvin scale,
there is a reference
point called absolute
zero, which is defined
as a temperature of 0
Kelvins. Absolute
zero is impossible to
reach.
• Measurement related
to the quantity of
molecules.
• Thermal energy
depends on the mass,
temperature, and
phase(solid, liquid, or
gas) of an object.
• As the temperature of
an object rises so does
its thermal energy.
• Thermal energy always moves from warmer
to cooler objects.
• Heat is the result of molecules vibrating
quickly.
• Heat is moving energy.
• Transfer is the result of a difference in
temperature.
Calorimeter
•A calorimeter is an instrument used to measure
changes in thermal energy.
•Uses the principle that heat flows from a hotter
object to a colder object until both reach the same
temperature.
•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. Calorimeter is sealed to prevent
thermal energy from escaping.
•A heated piece of aluminum is
placed in water. The change in
temperature of the water is
measured.
Thermal energy absorbed by the
water is calculated using the
specific heat equation.
Calorimeter
Count Rumford (Benjamin
Thompson)
• Count Rumford used a
drill to make a cannon
in 1798.
• He discovered that
heat cannot be a form
of matter.
Thermal contraction and
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.
•Thermal expansion is used in glass thermometers.
As temperature increases, the alcohol in the tube
expands and its height increases. The increase in
height is proportional to the increase in
temperature.
Specific Heat
– The ability of a substance to absorb
heat energy (specific heat)
Different substances absorb heat at
different rates
-amount of energy required to raise the
temp. of 1 kg of material by 1 degree
Kelvin
– units: J/(kg·K) or J/(g·°C)
Specific Heat
Some things heat up or cool down faster than others.
Land heats up and cools down faster than water
Why does water have such a high specific
heat?
water
metal
Water molecules form strong bonds with each other; therefore it
takes more heat energy to break them. Metals have weak bonds
and do not need as much energy to break them.
Specific Heat Cont….
-The
lower a material’s specific
heat, the more it’s temperature
rises when a given amount of
energy is absorbed by a given
mass
-The greater the mass of the
object the more heat is absorbed
Temperature Conversions
• Formula (273+ºC)= Kelvin
How to calculate changes in thermal energy
Q = m x T x Cp
Q = change in thermal energy
m = mass of substance
T = change in temperature (Tf – Ti)
Cp = specific heat of substance
Practice Problems
1. A piece of iron at a temperature of 145°C cools off to 45°C. If the
iron has a mass of 10g and a specific heat of 0.449 J/g·oC, how
much heat is given up?
2. How much heat is required to warm 230 g of
water from 12°C to 90°C?
3. A 32-g silver spoon cools from 60°C to 20°C.
How much heat is lost by the spoon?
• The transfer of heat by
direct contact between
objects or particles.
• Heat transferred
through space.
• EXAMPLE: The
sun’s rays causing a
sunburn.
• Heat transferred by the
movement of
molecules within a
substance.
• Movement occurs
from warmer areas to
cooler areas.
• The movement of a substance that is caused
by differences in temperature and density.
• EXAMPLES: wind
boiling water
• NATURE WANTS
EVERYTHING TO BALANCE !
!
• Conductors are
materials that transfer
heat easily.
• Examples: metals like
copper and gold
• An insulator is a
material that does not
transfer heat easily.
• Examples:
• liquids and gases
• A jacket
Review
What type of heat transfer is involved?
1. Heating a room with a fireplace
2. Egg cooking in a frying pan
3. Roof of a house becoming hot
What is the formula for converting a Celsius
temperature to a Kelvin temperature?
What is the boiling point of water on the Kelvin scale?
What is the freezing point of water on the Kelvin
scale?
Questions
• What are the three types of heat
transfer?
• How is conduction different
from radiation?
References
Wilmot High School
Lexington