Transcript Document 7306747

大学物理（热学）
1) Review
2) Examples
3) Order and Disorder
2006-12-27
2016/5/23
1
Clausius’ deduction (1865)
e= W/ QH
= 1-QL/QH
=1-TL/TH
QL/ TL=QH /TH, QH/ TH-QL /TL =0
(Q/T)=0
dQrev
 T 0
dQrev
 T ?
dQrev
 T 0
T1
T2
T3
T4
T6
T5
T7
(Q1/ T1+Q2 /T2)+(-Q2 /T2 +Q3 /T3 )+…+ (-Q6 /T6 +Q7 /T7 )=0
b
( I )
a
a
dQ
T
 ( II ) 
b
b
dQ
T
0
( I )
a
b
dQ
T
 ( II ) 
a
dQ
dS 
T
dQ
T
Irreversible: e= W/ QH = 1-QL/QH < 1-TL/TH
QL/ TL>QH /TH
(Q/T)<0
dQrev
 T 0
b
( I )
a
a
dQ
T
 ( II ) 
b
b
dQ
T
0
( I )
b
dQ
T
 ( II ) 
a
dQ
T
a
B
dQ
SB  SA  
T
A
R&IR
B
dQ
SB  SA  
T
A
For isolated system: S  0
Clausius’ Statement
“The energy of the universe is a
constant. The entropy of the universe
approaches a maximum.”
Example 20-6
Entropy change in melting. A
1.00-kg piece of ice at 0oC melts
very slowly to water at 0oC. Assume
the ice in contact with a heat
reservoir whose temperature is only
infinitesimally greater than 0oC.
Determine the entropy change of (a)
the ice cube and (b) the heat
reservoir.
Example 20-7
Entropy change when mixing
water. A sample of 50.0 kg of water
at 20.0oC is mixed with 50.0 kg of
water at 24.0oC. Estimate the
change in entropy without using
calculus.
Example 20-8
Entropy changes in a free expansion.
Consider the adiabatic free expansion
of n moles of an ideal gas from volume
V1 to volume V2, where V2 > V1.
Calculate the change in entropy (a) of
the gas and (b) of the surrounding
environment. (c) Evaluate S for 1.00
mole, with V2 = 2.00 V1.
B
SB  S A 

dQ
T
A
B
dQ
T
A
SB  SA  
Second Law
“Natural processes tend to move
toward a state of greater disorder.”
等几率假定
S=kBlnW