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Summary of last lecture:
•polymers
•rubber elasticity
Preview of coming attractions:
•rubber elasticity
•biopolymers: proteins
Lecture 25
March 9, 2009
Reminders
•PS9 is optional, due Weds, 11:59 pm
•Final review, Thursday 7:30 pm, Baxter
1
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View Full Document Final exam will be quasicumulative, but will
emphasize material in lectures 1626
•chemical equilibrium
•kinetics
•organic chemistry and reaction mechanisms
•polymers and biopolymers
•material from the entire course may be incorporated
into problems
review session Thursday, 7:30 pm Baxter Hall
can email questions in advance
2
same policies as midterm/Quiz
Thermodynamics of rubber elasticity: summary
Hooke
’
s law:
f = kx
First law of thermodynamics:
dE = TdS + fdx
"
E
x
#
$
%
’
(
T
=
T
S
x
#
$
%
’
(
T
+
f
for a rubber band dE/dx ~ 0 (ideal gaslike), or
T
S
x
#
$
%
’
(
T
=
)
f
when a rubber band is stretched,
f
> 0 and
dS/dx
< 0
dE = dq + fdx
~ 0, giving
dq = fdx
a rubber band gives off heat when stretched
stretching is exothermic
3
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View Full Document For this model, we can calculate the entropy change
in extending a chain from the origin to a conformation
with an endtoend length = x:
"
S
=
S x
( )
#
S
0
( )
=
#
k
B
2
Nl
2
x
2
4
The entropy of an idealized 1D chain may be evaluated
from the Boltzmann entropy expression and a Gaussian
endtoend length distribution
S x
( )
=
k
B
ln
"
x
( )
"
x
( )
=
2
N
P x
( )
=
2
N
2
#
Nl
2
( )
1/2
e
$
x
2
/(2
Nl
2
)
( )
S x
( )
=
$
k
B
2
Nl
2
x
2
+
constant
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This note was uploaded on 09/25/2010 for the course CH 104 taught by Professor Bopanna during the Fall '09 term at UMBC.
 Fall '09
 Bopanna
 Polymer

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