Thefugacityisdefinedin

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Unformatted text preview: s
providing
criteria
for
the
spontaneity
of
processes
occurring
either
 at
constant
V
and
T
or
at
constant
P
and
T,
the
Helmholtz
and
Gibbs
Free
 Energies
have
further
significant
meanings.
 Let
us
consider
first
the
case
of
the
Helmholtz
free
energy.
 The
second
law
states
that
dS
≥
δq
/
T.
Using
the
first
law
dU
=
δw
+
δq,
we
 get:
 T
dS
≥
dU
‐
δw
which
is
equivalent
to:
δw
≥
dU
‐
T
dS.
 If
the
process
occurs
at
constant
temperature,
then
we
can
write:
 δw
≥
dA
or
w
≥
DA
 If
we
focus
on
a
process
whereby
work
is
being
done
by
the
system

 (w
<
0).
We
now
recall
from
the
discussion
of
reversible
vs.
spontaneous
 expansions
of
ideal
gases
that
the
maximum
work
of
expansion
is
done
by
 the
system
when
the
expansion
occurs
reversibly.

This
corresponds
to
the
 equality
between
w
and
ΔA.

We
therefore
conclude
that:
 Δ A
is
the
maximum
work
that
can
be
done
by
a
system
at
constant
 temperature.
This
is
actually
why
the
symbol
A
was
chosen
for
the
 Helmholtz
Free
Energy.
In
German,
A
stands
for
“Arbeit”,
which
in
English
 means
“work”.
 Marand’s
Notes:
Chapter
3
‐
The
Second
Law
of
Thermodynamics
 120
 
 Let
us
consider
now
the
meaning
of
ΔG.
 Using
a
similar
approach,
we
write
the
first
law
in
its
most
general
form.
 dU
=
δw
+
δwe
+
δq
 where
δw
is
the
volume
expansion
work
and
δwe
is
any
extra
(non‐ expansion)
work.
 We
now
use
the
second
law
in
the
Clausius
formulation.
 dS
≥
δq
/T
 which...
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This note was uploaded on 01/26/2014 for the course CHEM 3615 taught by Professor Aresker during the Spring '07 term at Virginia Tech.

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