Chapter 12: Thermal Energy
What’s hot and what’s not…
Energy Wheel
Motion Energy
1 2
K.E.  mv
2
Wave Energy
Thermal Energy

Height Energy
P.E.  mgh

Electrical Energy
12.1
Temperature and
Thermal Energy
12.1 Objectives
Describe the nature of thermal energy.
Define temperature and distinguish it from
thermal energy.
Use the Celsius and Kelvin temperature
scales and convert between the two scales.
Define specific heat and calculate heat
transfer.
Thermodynamics
Thermodynamics is the study of heat.
Kinetic-Molecular Theory - matter is made
up of tiny particles in motion. In hot objects
(high energy) the particles move faster, and in
cold objects (low energy) they move more
slowly. The electromagnetic forces can be
thought of as mass-less springs between the
molecules.
Thermal Energy versus Temperature
Thermal Energy versus Temperature
Thermal Energy is the overall energy of motion of
all particles making up the object. Thermal energy
depends on the number of particles in the object.
Twice the mass gives twice the thermal (kinetic)
energy.
Temperature is the “hotness” of the object.
Temperature does NOT depend on the number of
particles in a body. It depends on the average
kinetic energy of the particles. Twice the mass
gives the same temperature.
Temperature Scales
Temperature is a measure of an object’s “hotness”.
Absolute zero is the temperature where all molecular
motion stops. All thermal energy is removed.
Farenheit and Rankin
R  F  459.67
Celcius and Kelvin
K  C  273.15
5
C  (F  32)
 9
Temperature Scales
Liquid Nitrogen
Thermal Energy Transfer
Heat flows from hot to cold.
Conduction - the process where heat is transferred
when particle collide. The pan handle gets hot as the
pan is heated.
Convection - the process where heat is transferred
by the motion of a fluid. The air from the room heater
is blown out on the ground and rises to create
circulation.
Radiation - the process where heat is transferred by
electromagnetic waves. The sun heats the earth from
millions of miles away.
Walking on Coals

Specific Heat
The Specific Heat of a material is the amount of
energy that must be added to the material to raise the
temperature of a unit mass one temperature unit.
Q  mCT  mC(Tfinal  Tinitial)
Q  Joules of Energy; m  mass; C  specific heat
Specific Heat Measurement
Calorimeter - A well insulated device used to measure
changes in thermal energy.
Air is a Poor Conductor
12.2
Change of State &
Laws of
Thermodynamics
12.2 Objectives
Define heat of fusion and vaporization.
State the first and second laws of
thermodynamics.
Define heat engine, refrigerator, and
heat pump.
Define entropy.
Change of State
Four States of Matter: solid, liquid,
vapor, and plasma.
At the melting point and boiling point all energy goes to the change of state.
The temperature stays constant until every molecule has changed state.
Heat of Fusion
The Heat of Fusion of a material is the amount of
energy that must be added to melt it. This seems
counter-intuitive. It should be the heat of melting
because fusion is making a solid from a liquid.
Q f  mH f
Note Bene: There is NO change in temperature term since temperature is
constant during the process.

Heat of Vaporization
The Heat of Vaporization of a material is the amount
of energy that must be added to vaporize it.
Qv  mHv
Note Bene: There is NO change in temperature term since temperature is
constant during the process.

Summary of Formulas
The Heat of Vaporization of a material is the amount
of energy that must be added to vaporize it.
Qv  mHv
Q f  mH f
QI  mCI T

QW  mCW T

QV  mCV T
First Law of Thermodynamics
The First Law of Thermodynamics states that the
total increase in thermal energy of a system is the sum
of the heat added to it and the work done on it.
ETHERMAL  W  HADDED
This is a restatement of the Law of Conservation of Energy:
Energy
 is neither created nor destroyed but can change form.
Second Law of Thermodynamics
Entropy is a measure of the disorder of a system.
The Second Law of Thermodynamics states that
natural processes go in a direction that maintains or
increases the total entropy of the universe. Things tend
to become more and more disordered.
Food color drops added to a glass of water demonstrates
diffusion and the second law of thermodynamics.
Second Law of Thermodynamics
Engines and Pumps
Heat Engine - converts heat
energy to work. Heat reservoir
produces work and gives heat
to cold reservoir.
Car Engine – Can you follow
the motion of a piston around
the cycle when gas explodes?
Engines and Pumps
Heat Pump - uses work to
remove heat energy. Work
removes heat from cold
reservoir to a heat reservoir.
Engines and Pumps
Heat Pump - uses work to
remove heat energy. Work
removes heat from cold
reservoir to a heat reservoir.
Refrigerator – Can you follow
the motion of a piston around
the cycle when gas explodes?