The First Law of Thermodynamics in Science Lectures

 
Thermodynamic science
Sixth Lecture
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Dr. Jasim Al-zanganawee
Diyala University
College of Science
Department of physics
Second stage
 
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Interpret & use 1
st
 law of thermodynamics.
Why 
internal energy 
of ideal gas depends on
temperature only.
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The first law of thermodynamics
 says the change in
internal energy of a system is equal to the heat flow into
the system mins the work done by the system
(conservation of energy).
First law of thermodynamics = general reflection of
conservation of energy
.
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القانون الأول للديناميكا الحرارية = الانعكاس العام للحفاظ على الطاقة
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-- Heat and work are forms of energy transfer and
energy is conserved
.
 
 
U   =   Q  +  W
on
 
work done
on
  the system
 
change in
total internal energy
 
heat added
to system
 
or
U   =   Q  -  W
by
 
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U
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=
 
+
Q
 
i
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W
 
o
u
t
 
Types of 
+Qin: 
انواع الطاقة الحرارية
Chemical Energy
 (Gasoline, Diesel) through combustion
مثل الطاقة الكيميائية (البنزين والديزل) من خلال الاحتراق
Conduction of Heat from 
Hot reservoir
(steam from a boiler or nuclear power plant)
مثل توصيل الحرارة من الخزان الساخن (البخار من مرجل أو محطة طاقة نووية)
Absorption of heat
 from solar energy
امتصاص الحرارة من الطاقة الشمسية
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Types of 
–W 
out
:
انواع الشغل والذي نوع من انواع الطاقة
Expansion of Pistons
 (Internal combustion & steam engines)
توسيع المكابس (محركات الاحتراق الداخلي والبخار)
Turning of a rotor
 (solar powered fan)
تحول الدوار في الماكنة  (مروحة تعمل بالطاقة الشمسية)
U
internal
 = 
+Q
 in
 
W 
out
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Both 
Q
 & 
W
 depend on path chosen between states…
But net change of internal U depends on 
change in T
 only…
 
  
is 
independent
 
of
 
path
!
If changes are infinitesimal, first law =
   
dU
 = 
dQ
dW
.
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Suppose more heat is added to system 
+ Q 
in
than system does work 
+W 
by gas 
by expanding.
Internal energy of system increases (
gas heats up!)
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Suppose heat added TO system 
+ Q 
in 
equals
work done BY system 
+W 
by gas
Internal energy of system is unchanged (no change in T)
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Suppose more heat flows out of system 
- Q 
in 
than work is done ON the gas 
-W
 on gas
Internal energy of system decreases (
gas cools!)
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E
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:
 
2
5
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u = +2500 J – (1800J) = +700 J
 
u
internal
 = +
Q
 in
W 
out
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Example: 2500 J of heat is added to a gas under a piston in
a closed cylinder, and 1800 J of work is done on the system
as the piston is pushed back down.
What is the change in internal energy of the system?
 
U
internal
 = +
Q
 in
W 
out
 
U
 
=
 
+
2
5
0
0
 
J
 
 
(
-
1
8
0
0
J
)
 
=
 
+
4
3
0
0
 
J
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Your body is a thermodynamic system.
Do a push-up!
Your body does work!
W
by system
 
> 0
.
Your body also warms up during exercise; by perspiration &
radiation & conduction, body gives off this heat, so 
Q
in
 < 0
.
Since 
Q
in
 
 negative & 
W
by system
 
positive,
   
U
 = 
Q
W
 < 0
Your body’s internal energy decreases.
Exercise helps you lose weight, using up some of internal energy stored in your
body in form of fat.
يسخن جسمك أيضًا أثناء التمرين. عن طريق العرق والإشعاع والتوصيل ، الجسم يعطي قبالة
هذه الحرارة ، لذلك
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Both 
Q
 & 
W
 depend on path chosen between states…
But net change of internal E depends on 
change in T
 only…
 
  
is 
independent
 
of
 
path
!
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0
I
n
t
e
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a
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e
n
e
r
g
y
 
Internal energy of coffee
depends on just its
thermodynamic 
state 
how much water & ground
coffee it contains,
& its 
temperature
.
تعتمد الطاقة الداخلية للقهوة على حالتها الحرارية - مقدار الماء والقهوة التي
تحتوي عليها ، ودرجة حرارتها
Internal energy does  
NOT
  depend on history of how coffee
was prepared— (thermodynamic path leading to current state)
لا تعتمد الطاقة الداخلية على تاريخ كيفية تحضير القهوة - (المسار الديناميكي
الحراري الذي يؤدي إلى الحالة الراهنة)
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Explore the concept of the First Law of Thermodynamics through a series of engaging science lectures by Dr. Jasim Al-zanganawee from Diyala University. Learn about energy transfer, conservation, internal energy of ideal gases, and how heat and work impact a system's total energy. Discover the relationship between heat flow, work done, and changes in internal energy, with practical examples from various sources like combustion and conduction of heat. Gain insights into the importance of path chosen between states and the impact of temperature changes on internal energy.

  • Thermodynamics
  • Science Lectures
  • First Law
  • Energy Transfer
  • Conservation

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  1. Thermodynamic science Sixth Lecture First law of thermodynamic system Dr. Jasim Al-zanganawee Diyala University College of Science Department of physics Second stage

  2. Learning Goals for this lecture Page 1 Interpret & use 1st law of thermodynamics. Why internal energy of ideal gas depends on temperature only.

  3. First law of thermodynamics -- Heat and work are forms of energy transfer and energy is conserved. . The first law of thermodynamics says the change in internal energy of a system is equal to the heat flow into the system mins the work done by the system (conservation of energy). = First law of thermodynamics = general reflection of conservation of energy. Page 19

  4. First law of thermodynamics -- Heat and work are forms of energy transfer and energy is conserved. U = Q + Won change in work done on the system heat added to system total internal energy State Function Process Functions or U = Q - Wby . 4 Page 20

  5. First law of thermodynamics Uinternal = +Q in W out Types of +Qin: Chemical Energy (Gasoline, Diesel) through combustion ) ( Conduction of Heat from Hot reservoir (steam from a boiler or nuclear power plant) ) ( Absorption of heat from solar energy Page 21

  6. First law of thermodynamics Uinternal = +Q in W out Types of W out: Expansion of Pistons (Internal combustion & steam engines) ) ( Turning of a rotor (solar powered fan) ) ( Page 22

  7. First law of thermodynamics Both Q & W depend on path chosen between states But net change of internal U depends on change in T only is independentofpath! If changes are infinitesimal, first law = dU = dQ dW. Page 23

  8. First law of thermodynamics Suppose more heat is added to system + Q in than system does work +W by gas by expanding. Internal energy of system increases (gas heats up!) Page 24

  9. First law of thermodynamics Suppose heat added TO system + Q in equals work done BY system +W by gas Internal energy of system is unchanged (no change in T) Page 25

  10. Example :Using the first law. Suppose more heat flows out of system - Q in than work is done ON the gas -W on gas Internal energy of system decreases (gas cools!) Page 26

  11. First law of thermodynamics Example: 2500 J of heat is added to a gas under a piston in a closed cylinder, and 1800 J of work is done by the system as its piston expands. What is the change in internal energy of the system? uinternal = +Q in W out u = +2500 J (1800J) = +700 J Page 27

  12. Example :Using the first law. Example: 2500 J of heat is added to a gas under a piston in a closed cylinder, and 1800 J of work is done on the system as the piston is pushed back down. What is the change in internal energy of the system? Uinternal = +Q in W out U = +2500 J (-1800J) = +4300 J Page 27

  13. First law of exercise thermodynamics Your body is a thermodynamic system. Do a push-up! Your body does work! Wby system> 0. Your body also warms up during exercise; by perspiration & radiation & conduction, body gives off this heat, so Qin < 0. . Since Qinnegative & Wby systempositive, U = Q W < 0 Your body s internal energy decreases. Exercise helps you lose weight, using up some of internal energy stored in your body in form of fat. Page 29

  14. First law of thermodynamics Both Q & W depend on path chosen between states But net change of internal E depends on change in T only is independentofpath! Page 30

  15. Internal energy Internal energy of coffee depends on just its thermodynamic state how much water & ground coffee it contains, & its temperature. - Internal energy does NOT depend on history of how coffee was prepared (thermodynamic path leading to current state) - ( ) Page 31

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