entropy

1. Ahmed Medhat - Thermodynamics 1 - ahmedhatfa@hotmail.com
Reversibility , Irreversibility, Entropy in pure substance , Entropy change.
PT.02

2. Ahmed Medhat - Thermodynamics 1 - ahmedhatfa@hotmail.com
P
v
1
2
ර
𝛿𝑄
𝑇
=
𝛿𝑄𝐻
𝑇
⃒A -
𝛿𝑄𝐿
𝑇
⃒B
A
B
C
ර
𝛿𝑄
𝑇
=
𝛿𝑄𝐻
𝑇
⃒C -
𝛿𝑄𝐿
𝑇
⃒B
ර
𝛿𝑄
𝑇
≤ 0
0
𝛿𝑄𝐻
𝑇
⃒C
𝛿𝑄𝐻
𝑇
⃒A
Independent of the path
𝛿𝑄𝐻
𝑇
Pressure ( P ) Temperature ( T ) Enthalpy ( H )
Entropy ( S )

3. Ahmed Medhat - Thermodynamics 1 - ahmedhatfa@hotmail.com
Entropy ( S ) All things trend toward disorder.
Entropy is simply a measure of disorder
Independent of the path
𝛿𝑄𝐻
𝑇 Entropy ( S )

4. Ahmed Medhat - Thermodynamics 1 - ahmedhatfa@hotmail.com
Entropy ( S )
ර
𝛿𝑄
𝑇
≤ 0
Reversible Irreversible
𝑑𝑆 =
𝛿𝑄
𝑇
𝑑𝑆 >
𝛿𝑄
𝑇
ර
𝛿𝑄
𝑇
ර
𝛿𝑄
𝑇
0 0
P
v
1
2
A
B
Reversible
ර
𝛿𝑄
𝑇
= ‫׬‬
1
2 𝛿𝑄𝐻
𝑇
⃒A + ‫׬‬
1
2 𝛿𝑄𝐻
𝑇
⃒B = 0
𝛿𝑄𝐻
𝑇
⃒C
𝛿𝑄𝐻
𝑇
⃒A
ර
𝛿𝑄
𝑇
= ‫׬‬
1
2 𝛿𝑄𝐻
𝑇
⃒c + ‫׬‬
1
2 𝛿𝑄𝐻
𝑇
⃒B < 0
𝛿𝑄
𝑇
⃒irreversible < 𝑑𝑆
c

5. Ahmed Medhat - Thermodynamics 1 - ahmedhatfa@hotmail.com
𝛿𝑄
𝑇
⃒irreversible < 𝑑𝑆
𝑆2 − 𝑆1 = ‫׬‬1
2 𝛿𝑄𝐻
𝑇
+𝛿𝑆𝑔𝑒𝑛
𝛿 𝑆𝑆𝑈𝑅𝑅𝑂𝑈𝑁𝐷𝐼𝑁𝐺
Temperature ( T0 )
Q
𝑊
𝑆𝑆𝑈𝑅 =
−𝑄
T0
𝛿𝑆𝑆𝑌𝑆𝑇𝐸𝑀
𝐿𝑖𝑞𝑢𝑖𝑑 & 𝑆𝑜𝑙𝑖𝑑
𝐺𝑎𝑠
𝛿𝑆 = 𝑚 𝐶𝑣 ln(
𝑇2
𝑇1
)
𝛿𝑆 = 𝑚 𝐶𝑣 ln(
𝑇2
𝑇1
) + m R ln(
𝑣2
𝑣1
)
𝑷𝟐
𝑷𝟏
=
𝝆𝟐
𝝆𝟏
𝜰
=
𝒗𝟏
𝒗𝟐
𝜰
=
𝑻𝟐
𝑻𝟏
𝜰
𝜰 −𝟏
Isentropic relations

6. Ahmed Medhat - Thermodynamics 1 - ahmedhatfa@hotmail.com
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