2nd Law of Thermo
• Heat flows spontaneously from a substance
at a higher temperature to a substance at a
lower temperature and does not flow
spontaneously in the reverse direction.
• Heat flows from hot to cold.
• Alternative: Irreversible processes must
have an increase in Entropy; Reversible
processes have no change in Entropy.
• Entropy is a measure of disorder in a system
Entropy on a Microscopic Scale
We can treat entropy from a
microscopic viewpoint through
statistical analysis of molecular
motions.
A connection between entropy and
the number of microstates (W) for a
given macrostate is
S = kB ln W
 The more microstates that
correspond to a given
macrostate, the greater the
entropy of that macrostate.
This shows that entropy is a measure
of disorder.
Section 22.8
Entropy
Reversible and Irreversible Processes
The Arrow of Time!
Play the Movie Backwards!
https://www.youtube.com/watc
h?v=yKbJ9leUNDE
https://www.youtube.com/watch?v=GdTMuivYF30
Heat Death of the Universe
Ultimately, the entropy of the
Universe should reach a
maximum value.
At this value, the Universe will
be in a state of uniform
temperature and density.
All physical, chemical, and
biological processes will cease.
The state of perfect disorder
implies that no energy is
available for doing work.
This state is called the heat
death of the Universe.
Entropy
https://www.youtube.com/watch?v=yKbJ9leUNDE
Big Bang Cosmogenesis
The Stellar Age
Stars Rule for a Trillion Years
In about 5 billion years,
Our Sun will swell into a cool Red Giant,
engulfing Mercury, Venus and possibly Earth!
The Degenerate Age
After about 100 trillion, years, the stars are dead.
By 1037 years, the material in the "Local Galaxy"
consists of isolated stellar remnants and black holes.
Everything is cold and dark.
The Black Hole Age
All the stars turn into black holes.
After about 10100 years, all the black holes are gone.
The Dark Era
The remaining black holes evaporate: first the small ones, and
then the supermassive black holes. All matter that used to
make up the stars and galaxies has now degenerated into
photons and leptons.
Boltzmann was subject to rapid alternation of depressed
moods with elevated, expansive or irritable moods, likely the
symptoms of undiagnosed bipolar disorder. On September 5,
1906, while on a summer vacation in Duino, near Trieste,
Boltzmann hanged himself during an attack of depression.
He is buried in the Viennese Zentralfriedhof; his tombstone
bears the inscription.