The document discusses the first law of thermodynamics and its application to several processes including isothermal, isobaric, isochoric, and adiabatic. It provides the mathematical equations relating work, heat, and changes in internal energy for these different processes. It also includes several student activities applying the concepts to example systems and calculating work, heat, and energy changes.

1. Laws of
Thermodynamics 1
Disusun Oleh :
Ichwan Aryono, S.Pd.

2. First law of thermodynamics
First Law of thermodynamics states that :
Whenever heat Q is given to a system, a portion of heat is used to
increase its internal energy in the amount of ∆U, whereas the
remaining leaves the system when the system performs a work W to
its surroundings.
Mathematically, the first law of thermodynamics is formulated by :
Q>0 Q = ∆U + W
W positip jika sistem melakukan usaha
W negatip jika sistem dikenai usaha
Q positip Jika sistem menerima kalor
W>0 W<0
Q negatip jika sistem melepas kalor
Energi dalam ∆U tidak terpengaruh oleh proses,
yang dilihat adalah hanya pada keadaan awal dan
keadaan akhir
Q<0

3. The first law of thermodynamics for isothermal
process
At isothermal Process : ∆T = 0, so ∆U = 0
The work done by the isothermal process is :
V2 so
W = nRT ln
V1
Q = ∆U + W = 0 + W = W
V2
Q = W = nRT ln
V1

4. The first law of thermodynamics for isobaric
process
At isobaric process the pressure is constant
DP = 0
3
Internal energy ∆U = P∆V , so
2
3
Q = ∆U + W = P∆V + P∆V
2
5 5
Q = P∆V = P (V2 − V1 )
2 2

5. The first law of thermodynamics for
isochoric process
At Isochoric process volume is constant, ∆V = 0,
so the work done W = P∆V = 0, its produce :
Q = ∆U + W = ∆U + 0
3 3
Q = ∆U = nR∆T = nR (T2 − T1 )
2 2

6. The first law of thermodynamics for adiabatic
process
Adiabatic process is a process without any transfer
of heat into or from the system (Q=0)and it applies
:
Q = ∆ +W
U
0 = ∆ +W
U
3
W = −∆ = − nR (T2 −T1 )
U
2
3
W = nR (T1 −T2 )
2

7. Student Activity #1
A system absorbs 1500 J of heat from surrounding and does
work done 2200 J . Determine the change of internal energy
system, increases or decreases ?

8. Student Activity #2
System absorbs 1500 J of energy from surrounding. At the
same time 2200 J work done is given to the system.
Determine the change of internal energy of the system. Is
temperature decreses or increases ?

9. Student Activity #3
Two mol of ideal gas is expans from point I to point F with
three difference way as shown in diagram below.
Calculate the work done, change of internal energy, and
calor in each way IAF, IF and IBF, state in joule
P(atm) A
4
I
B F
1
V(L)
2 4

10. Student Activity
P(Pa)
Four mol of ideal gas in
cylinder container change B A
its conditional as shown in 500
graphic P-V beside.
Determine the work done,
internal energy and calor if
the gas is change from A to C
200
C thrue (a) ABC, (b) AC
V(cm3)
0
300 500 800

11. Student Activity #5
Three different processes act on system.
a. In process A, 42J of work are done on the system and 77J of
heat are added to the system. Find the change in the
system’s internal energy.
b. In process B. the system does 42 J of work and 77J of heat
are added to the system. What is the change in the system’s
internal energy ?
c. In process C, the system’s internal energy decreases by 120
J while the system performs 120 J of work on its
surroundings. How much heat was added to the system ?

12. Student Activity #6
An ideal gas is taken through the four processes shown in
figure below. The changes in internal energy for three of
these processes are as follows : ∆UAB = + 82 J, ∆UBC =
+15 J, ∆UDA = -56 J. Find the change in internal energy
for the process from C to D
D C
pressure
A B
volume

13. Student Activity # 7
a. Find the work done by a monoatomic ideal gas as it
expands from point A to point C along the path shown in
figure below.
b. If the temperature of the gas is 220K at point A, what is its
temperature at point C ?
c. How much heat has been added to or removed from the
gas during this process ?
B
600
Pressure P(kPa)
400
A C
200
Volume, V(m3)
0 2 4 6 8 10

14. Student Activity #8
During an adiabatic process, the temperature of 3.52 moles
of monoatomic ideal gas drops from 485oC to 205oC. For
this gas, find
a. The work it does
b. The heat it exchanges with its surroundings, and
c. The changes in internal energy

15. Student Activity #9
An ideal gas follows the three-part process shown in figure
below. At the completion of one full cycle, find
a. The net work done by the system
b. The net change in internal energy of the system
c. The net heat absorbed by the system
A
150
Pressure P(kPa)
100
B
50 C
0 1 2 3 4 Volume, V(m3)

16. Quiz
Suppose 57.5 moles of an ideal monoatomic gas undergoes
the series of processes shown in figure below.
a. Calculate the temperature at the points A, B, and C.
b. For each process, A-B, B-C, and C-A, state whether heat
enters or leaves the system, Explain in each case.
c. Calculate the heat exchanged with the gas during each of
three process.
A
150
Pressure P(kPa)
100
B
50 C
0 1 2 3 4 Volume, V(m3)