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# 熵及熵增原理 - PowerPoint PPT Presentation

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Presentation Transcript

§6

1. 熵的定义： S

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S = k lnW

W 热力学几率函数， k 玻尔兹曼恒量

2. 热力学第二定律的统计意义：

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2. 热力学第二定律的统计意义：

3. 熵变:

W2

= kln

W1

= klnW2 - klnW1

DS = S2- S1

DS > 0

DS = 0

DS ≥ 0

d

Q

2

ò

D

S

=

T

1

1. 熵是系统状态的单值函数

2. 对于可逆过程熵变可用上式进行计算

3. 若过程不可逆，则不能直接用上式。

1、2 两物体 ( T1 > T2 ) 为一孤立系统，发生热传导这一过程是不可逆的。

d

Q

d

Q

T

T

2

1

dQ

T

T

-

+

dT

dT

T1

T2

2

1

Q

d

Q

T

T

2

1

d

Q

d

Q

T

T

2

1

d

Q

d

Q

0

>

T

>

T

T

T

1

2

2

1

1. 熵是状态函数。熵变和过程无关，它

2. 对于非孤立系统，熵有可能增加，

3. 熵反映了能量的品质因数，熵越大，

4.不能将有限范围得到的熵增原理外推

[例1]

d

Q

Q

2

m

h

ò

S

S

=

=

=

2

1

T

T

T

1

1

334

×

=

273.15

1(kg)冰融成水的熵变。

=1.22(KJ.K-1)

[例2]

T

m

c

d

d

Q

T

2

2

ò

ò

p

S

S

=

=

T

T

2

1

T

1

1

T

T

d

T

2

ln

ò

m

c

m

c

2

=

=

p

p

T

T

T

1

1

373.15

3

1

4.18

10

ln

=

×

×

×

273.15

)

3

1.30

10

J.K

(

=

1

×

cp =4.18×103(J.kg-1.K-1)