Thermodynamics Flashcards
the object or collection of objects
under study (steam, an engine, or a human
body)
System
everything around the system
Surroundings
made up of the system and the
surroundings
Universe
refers to the sum of the kinetic
energies of the molecules of a body and the
potential energy due to inter-molecular forces.
Internal energy
process is one in which the system
and its surroundings can be returned to their
initial state before the process occurs (e.g water
to ice, ice to water). The opposite, of course, is
irreversible. Growing old, breaking a glass, and
burning pieces of papers are irreversible
process. Fusion, vaporization, sublimation,
expansion, and contraction of substances when
heat is added or released are examples of
reversible process.
Reversible
‘thermos’ and ‘dynamikos’
Heat and Power
formulated the first concise
definition of thermodynamics: Thermodynamics is
defined as the subject of the relation of heat to
forces acting between contiguous parts of bodies,
and the relation of heat to electrical agency.
Lord Kelvin (1854)
One regular – sized pan de sal
can give you 100kcal of heat. When you eat,
you are storing energy in your body. This
increases the total internal energy in the
body. However only about one-fourth of the
food energy is used by your muscles to do
work. The rest is used to maintain internal
bodily functions. For example, diet and
exercise is a very effective way to shed off
unwanted fats
`Your body
is generated when water is
heated to its boiling temperature. The
source of heat may be firewood, coal,
charcoal, oil, gas, or electricity. Under
normal conditions, when water evaporates
it expands to 1 600 times its normal volume.
If the water is confined, the steam evolved
will exert a considerate amount of pressure
which can be utilized to do work.
Steam
Gas fuels, like methane and
water gas, can generate a great amount of
heat when burned. The heat given off by the
burning gas may be utilized to vaporize a
liquid under pressure.
Burning Gas
If object A is in thermal equilibrium with object B
and object A is in thermal equilibrium with a third
object C, then object B must be in equilibrium with
object C.’
Zeroth Law of Thermodynamics
‘When heat flows to or from a system, the system
gains or loses an amount of energy equal to the
amount of heat transferred.’
First Law of Thermodynamics
Kelvin – Planck Statement. No heat engine
can completely convert heat energy to work.
In other words, there is no 100% efficient
heat engine.
b. Clausius Statement. Heat flow naturally from
hot to cold objects.
c. Entropy Statement. When a reversible
process occurs, the total entropy of the
universe remains the same. When an
irreversible process occurs, the total
entropy of the universe increases.
Second Law of Thermodynamics
The entropy of a pure crystal at absolute
zero is zero. As explained, entropy is the
thermodynamic measure of the disorder of a
system or sometimes called as “waste energy”,
energy that is unable to do work, and since no heat
energy whatsoever at absolute zero, there can be
no waste energy. The absolute zero is the
temperature at which molecules stop moving.
While a perfect crystal is by definition perfectly
ordered, any positive value of temperature means
there is motion within the crystal, which caused
disorder. For these reasons, there can be no
physical system with lower entropy, so entropy has
a positive value.
Third Law of Thermodynamics
is the thermodynamic measure of
disorder. In other words, in any closed system,
objects are getting more and more mixed. Mixtures
don not ‘unmix’ by themselves. Entropy is
represented by S.
Entropy
