Download 11-Heat Energy

Energy in Thermal
Processes
Chapter 11
Internal Energy
Internal energy, U, is the sum total of all types of
energy possessed by a system of atoms or
molecules.
Internal energy can include random kinetic
energy of linear motion, rotational motion,
vibrations, and intermolecular potential energy.
James P. Joule
Studied the relationship between heat and
mechanical energy
The unit of energy was named after him
1 calorie = 4.186 Joules
1 Calorie = 4186 Joules
Heat Capacity
Heat Capacity is a measure of how much heat energy
must be added to raise the temperature of an object.
A large heat capacity means that a lot of heat must be
added transferred to raise the temperature of the
object by a given amount.
A bigger object of the same material has a bigger
heat capacity.
Specific Heat Capacity
Is the heat capacity per unit mass of a material.
It does not depend on how large the object is –
only what it is made of.
Its name is often shortened to just “specific heat”.
Specific Heats for Various
Materials
Note that water has one of the
highest values of specific heat.
Materials with heavy elements,
such as gold and lead have
much smaller specific heats.
Latent Heat
Q = ± m L is the amount of heat added or
removed during a phase transition.
Heat Conduction
When two materials at
different temperatures are
placed in contact, heat
flows from the hotter one
to the cooler one by the
process of conduction.
Heat Conduction
The rate of heat conduction
depends on the difference in
temperature across the material,
the thickness, the area the heat
if flowing through and the
thermal conductivity, k.
Thermal Conductivity
The thermal conductivity of a
material is a measure of how well
it conducts heat.
Insulation
Poor thermal conductors reduce
the amount of heat conducted.
The fiberglass insulation works
by trapping a layer of air (which
is a poor heat conductor).
Double-paned windows work
the same way
R-Values
R = L / k is a measure of
the resistance to heat flow
of a material.
Higher R-Values mean
better insulation
The R-Values of successive
layers add together.