P temperaturedependenceofthegibbsfreeenergy

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Unformatted text preview: therefore
no
disorder.
 Marand’s
Notes:
Chapter
3
‐
The
Second
Law
of
Thermodynamics
 116
 
 Helmholtz
and
Gibbs
Free
Energies
 We
have
discussed
at
some
length
the
Second
Law
of
Thermodynamics,
 which
provides
criteria
for
spontaneity
and
reversibility
applicable
to
any
 processes.
 ΔSUnivese
=
ΔS
+
ΔSSurr
>
0
for
a
spontaneous
process
and
ΔSUniverse
=
0for
a
 reversible
process
or
for
conditions
of
equilibrium.

Such
criteria
although
 very
useful
are
not
extremely
practical
as
they
require
us
to
carry
out
 calculations
for
both
the
system
and
the
surroundings.

It
would
be
 extremely
advantageous
to
find
criteria
for
spontaneity,
which
are
based
on
 the
use
of
thermodynamic
state
functions
for
the
system
and
which
do
not
 invoke
the
surroundings.
This
can
be
done
under
the
specific
conditions
 (constant
volume
and
temperature
or
constant
pressure
and
temperature),
 which
are
encountered
in
many
processes
in
chemical,
physical
and
 materials
sciences.
 
 
 
 
 Marand’s
Notes:
Chapter
3
‐
The
Second
Law
of
Thermodynamics
 117
 Helmholtz
Free
Energy:

 Let
us
assume
we
are
dealing
with
a
process
occurring
at
constant
volume.

 The
heat
exchanged
with
the
surroundings
is
equal
to
change
in
internal
 energy.
 dU
=
δqV
 The
second
law,
written
in
the
form
of
the
Clausius
Inequality
states:

 dS
>
δq
/
T
 Note
that
this
inequality
comes
from
dS
+
dSSurr

>
0
and
dSSurr
=
‐
δq
/
T
 Therefore,
we
can
rearrange
this
equation
as
δq
‐
T
dS
<
0
since
T
is
always
 positive.
 This
leads
in...
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