2 casesofidealgasesvnrtp

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Unformatted text preview: 
the
case
of
a
process
at
constant
volume
to
dU
‐
TdS
<
0
 If
we
now
assume
T
to
be
constant,
we
get:
d(U
‐
TS)
<
0
 We
then
define
a
new
thermodynamic
function,
A,
the
Helmholtz
free
 energy
such
that:
A
=
U
‐
TS
 The
criteria
for
spontaneity
for
a
process
occurring
at
constant
volume
 and
temperature
is
therefore
dA
<
0.
In
contrast,
a
process
occurring
at
 constant
volume
and
temperature
will
be
reversible
or
will
have
reached
 some
equilibrium
state
if
dA
=
0.
 
 Marand’s
Notes:
Chapter
3
‐
The
Second
Law
of
Thermodynamics
 118
 
 Gibbs
Free
Energy:
 We
now
consider
processes
occurring
at
constant
pressure
and
constant
 temperature.
For
constant
pressure
processes,
the
heat
exchanged
with
the
 surroundings
is
equal
to
the
change
in
enthalpy.
 δqP
=
dH
 Therefore,
the
Clausius
Inequality
for
a
spontaneous
process,
which
occurs
 at
constant
pressure,
is
written
as:
 dS
>
dH
/
T







which
is
equivalent
to:
 dH
‐
T
dS
<
0
 If
the
process
furthermore
occurs
at
constant
temperature
then:
 d(H‐TS)
<
0
 We
then
define
a
new
thermodynamic
state
function,
G
=
H
‐
TS,
which
we
 call
the
Gibbs
Free
Energy.
 The
criteria
for
spontaneity
for
a
process
occurring
at
constant
pressure
 and
temperature
is
therefore
dG
<
0.
In
contrast,
a
process
occurring
at
 constant
pressure
and
temperature
will
be
reversible
or
will
have
reached
 some
equilibrium
state
if
dG
=
0.
 
 Marand’s
Notes:
Chapter
3
‐
The
Second
Law
of
Thermodynamics
 119
 Maximum
Work
Functions,
Δ A
and
Δ G
 Beside...
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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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