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Notes:
Chapter
3
‐
The
Second
Law
of
Thermodynamics
 113
 where
W
is
the
number
of
“configurations”
of
the
system
which
lead
to
the
 same
energy
of
that
system.
To
understand
the
concept
of
“configurations”
 of
a
system
we
will
consider
the
following
example:
When
we
consider
a
 material,
we
know
it
contains
atoms
or
molecules.
Let
us
assume
that
we
 represent
the
material
by
a
giant
three‐dimensional
cubic
lattice.

The
 material
can
then
be
represented
by
putting
molecules
at
these
lattice
 sites.

When
we
consider
a
solid
at
0
K,
all
lattice
sites
are
occupied,
we
 have
a
perfect
crystal.

At
intermediate
temperatures,
we
willhave
a
liquid.
 When
the
material
is
in
the
liquid
state,
most
of
the
lattice
sites
are
 occupied,
but
some
are
vacant.
The
existence
of
a
number
of
vacant
sites
is
 required
by
the
fact
that
liquids
have
generally
a
slightly
lower
density
than
 solids
but
also,
remember
that
liquids
flow,
the
vacant
sites
are
necessary
 for
flow
to
take
place.

Since
it
is
not
easy
to
make
three‐dimensional
 representations
of
such
objects,
let
us
represent
these
in
two
dimensions.
 We
assume
the
liquid
phase
to
have
31
molecules
and
the
solid
phase
to
 have
36
molecules.
The
solid
contains
36
lattice
sites.
 
 
 
 
 
 
 Marand’s
Notes:
Chapter
3
‐
The
Second
Law
of
Thermodynamics
 114
 LIQUID
PHASE
 For
the
liquid
phase
shown
on
the
lattice
on
the

 left,
the
number
of
configurations
is
calculated
 in
the
same
fashion.
 W
=
36!
/
(
5!
x
31!
)
because
there
are
36
sites,...
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