Coolingslowlythevapor

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Unformatted text preview: calculate
the
entropy
change
ΔS
=
SB
‐
SA
for
an
irreversible
process
 between
A
and
B,
one
cannot
integrate
δq
/
T,
the
ratio
of
the
heat
 increment
over
the
temperature,
along
the
actual
path
followed
during
the
 A‐B
process,
since
dS
=
δq
/
T
only
applies
to
reversible
processes.
Indeed,
 the
second
law
states
that:
dS
>
δ q
/
T
for
an
irreversible
process.
 However,
since
the
entropy
is
a
state
function,
the
entropy
change
ΔS
does
 not
depend
on
the
path
chosen.
Since
we
know
how
to
calculate
entropy
 change
for
the
system
along
any
reversible
path,
we
will
imagine
a
 hypothetical
path
between
A
and
B
that
is
reversible.

We
will
now
 consider
some
examples
to
illustrate
this
concept.
 
 Example
1:

 Two
blocks
of
metal
A,
and
B,
of
masses
mA
and
mB,
initially
at
 temperatures
TA
and
TB
are
placed
in
contact
with
one
another
in
a
 thermally
insulated
container.

As
a
result
of
the
difference
in
their
initial
 temperatures
and
of
the
fact
that
they
are
placed
in
contact
with
each
 other,
they
will
exchange
heat
with
each
other
until
they
exhibit
the
same
 final
temperature,
TF.

Heat
is
exchanged
only
between
the
two
blocks
since
 Marand’s
Notes:
Chapter
3
‐
The
Second
Law
of
Thermodynamics
 102
 they
are
placed
in
a
thermally
insulated
container
(adiabatic
process).
 Considering
the
two
blocks
to
form
the
System,
no
heat
is
exchanged
 between
system
and
surroundings.
 Therefore:
q
=
qA‐B
+
qB‐A
=
0

 where
qA‐B
is
the
heat
received
by
A
from
B
(qA...
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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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