Thermal Energy
1. Temperature & Heat
Temperature is the measurement
of average kinetic energy of the
particles in a substance.
2. Units for temperature
a. SI standard is the Kelvin
b. Celsius is more common
3. Thermal Energy –
the total of all the
kinetic and potential
energy of all the
particles in a substance.
4. Thermal energy relationships
a. As temperature increases, so does
thermal energy (because the kinetic
energy of the particles increased).
b. Even if the temperature doesn’t
change, the thermal energy in a
more massive substance is higher
(because it is a total measure of
energy).
5. Heat
a. The flow of thermal
energy from one
object to another.
b. Heat alwaysflows from
warmer to
cooler objects. Ice gets warmer while hand gets
cooler
Cup gets cooler while hand gets warmer
6. Specific Heat
a. Some things heat up or cool
down faster than others.
Land heats up and cools down faster than water
b. Specific heat is the amount of heat
required to raise the temperature
of 1 kg of a material by 1o (C or K).
1) C water = 4184 J/kgoC
2) C sand = 664 J/kgoC
This is why land heats up quickly during the day and cools quickly at night and why water takes longer.
Why does water have such a high specific heat?
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.
water metal
How to calculate changes
in thermal energy
= change in thermal energy
= mass of substance
= change in temperature (Tf – Ti)
= specific heat of substance
Calculate the change in thermal energy of the water
in a pond with a mass of 1000 kg and a specific heat
of 4184 J/(kgoC) if the water cools by 1oC.
Calculate the specific heat of a metal if 0.5 kg of the
metal absorb 9000 J of heat as it warms by 10oC.
Find the change in thermal energy of a 20-kg wooden chair
that warms from 15º to 30º if the specific heat of wood
is 700 J/(kgº).
A concrete statue (specific heat = 600 J/kgoC) sits in
sunlight and warms up to 40oC. Overnight, it cools to 15oC
and loses 90 000 J of thermal energy. What is its mass?
c. A calorimeter is used to help measure
the specific heat of a substance.
First, mass and temperature of water are measured. The material is then heated, temp measured again. The sample is placed in the
water in the inner chamber, the sample cools as heat is transferred from the sample to the
water. When the temp of the sample & water are the same, a final temp is recorded.
Initial & Final Temp are known, the amount of heat gained can be calculated.