Download Day Nine Slides - University of Mount Union

2/3/10
Thermal
Energy
  ΔEth
=
W
+
Q
  W
=
work
done
on
system
  Q
=
heat
added
to
system
More
Work
and
Heat
  What
is
ΔEth?
Meaning
of
Temperature
Thermal
Energy
  We
can’t
change
ΔEth
without
changing
T
  Likewise,
any
change
in
T
means
a
change
in
ΔEth
  But
don’t
confuse
this
with
Q!
A
gas
cylinder
  The
piston
can
be
locked
in
place
A
gas
cylinder
M
=
M1
+
Mpiston
M1
  Consider
an
isochoric
cooling
process
  W
=
0
  How
can
we
cool
the
gas?
GAS
  Consider
isothermal
expansion
 
 
 
 
ΔT
=
0
What
else
=
0?
So
W
=
‐Q
Heat
the
gas
but
decrease
M
so
that
PV
=
constant
M
=
M1
+
Mpiston
M1
GAS
1
2/3/10
A
gas
cylinder
  Consider
isothermal
expansion
A
gas
cylinder
M
=
M1
+
Mpiston
  Consider
adiabatic
compression
M
=
M1
+
Mpiston
M1
is
NOT
zero!
M1
  Adiabatic
means
Q=0
  ΝΟΤΕ: ΔT
=
0
but
Q
GAS
  If
we
compress
the
GAS
gas,
W
>
0
  Will
ΔT
=
0?
Energy
storage
&
transfer
  Consider
two
blocks
of
equal
size
  The
left
block
starts
at
0
oC
  The
right
block
starts
at
100
oC
  What
will
happen?
Energy
storage
&
transfer
Temperature
Question
  Q
=
McΔT
  If
we
have
a
mass
at
  Gases:
  Q
=
nCVΔT
20
oC
and
we
double
its
temperature,
what
do
we
get?
  Q
=
nCPΔT
2