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5. (a) Since the gas is ideal, its pressure
p
is given in terms of the number of moles
n
, the
volume
V
, and the temperature
T
by
p = nRT
/
V
. The work done by the gas during the
isothermal expansion is
22
11
2
1
ln
.
==
=
³³
VV
dV
V
Wp
d
V
n
R
T
n
R
T
We substitute
V
2
= 2.00
V
1
to obtain
()
(
)
(
)
3
=
ln2.00 = 4.00 mol 8.31 J/mol K
400 K ln2.00 = 9.22 10 J.
Wn
R
T
⋅×
(b) Since the expansion is isothermal, the change in entropy is given by
1
ST
d
Q
Q
T
Δ=
=
³
,
where
Q
is the heat absorbed. According to the first law of thermodynamics,
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This note was uploaded on 06/03/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.
 Spring '08
 Any
 Physics, Work

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