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Kereta uap dapat berjalan dengan memanfaatkan energi uap 
179 
Bab 
8 
Termodinamika 
A. Usaha pada 
Berbagai Proses 
Termodinamika 
B. Hukum I 
Termodinamika 
C. Kapasitas Kalor Gas 
dan Siklus 
Termodinamika 
D. Hukum II 
Termodinamika 
Hasil yang harus Anda capai: 
menerapkan konsep termodinamika dalam mesin kalor. 
Setelah mempelajari bab ini, Anda harus mampu: 
,6;2=2? 56?82? A6B632?82? I22? C2B2?2 DB2?CA@BD2C: H2?8 
5:8E?22? 2?EC:2 D6BEC 36B632?8 122? 529E=E E52 52? 6B6D2 
E52 6?;25: AB:25@?2 2?8ED2? 52B2D ,22D :?: A6B2?2? E52 C63282: 
2=2D DB2?CA@BD2C: 52B2D CE529 D6B82?D:2? @=69 636B2522? @D@B @3:= 
52? 6B6D2 $6=63:92? 52B: C2B2?2 DB2?CA@BD2C: @56B? :?: 252=29 D6?282 
H2?8 5:92C:=2??H2 =63:9 36C2B 52B:A252 D6?282 E52 (=69 2B6?2 :DE 
;E=29 A6?EA2?8 52? 32B2?8 H2?8 52A2D 5:2?8ED AE? C62:? 32?H2 
)25252C2B?H2A6B632?82?C2B2?2DB2?CA@BD2C:D6BC63EDD:52=6A2C 
52B: 62;E2? D6?@=@8: 2A=:2C: AB:?C:A D6B@5:?2:2 !2A:B C6E2 
6C:? H2?8 252 6?88E?22? AB:?C:A D6B@5:?2:2 H2:DE 6?8E329 
6?6B8: 2=@B 6?;25: 6?6B8: 86B2 
yang diubah menjadi energi kinetik. 
menganalisis perubahan keadaan gas ideal dengan menerapkan hukum 
termodinamika. 
Sumber: Physics for Scientists and Engineers, 2000
Tes Kompetensi Awal 
#-5...1-+2*,0/31 2.0%*/.*,,2+,/-)30-30-#2*,54%-.#5,5-4*)/ 

 A229H2?85:2CE556?82?67:C:6?C:6C:? 
 6?EBED?522A229H2?85:2CE556?82?6?DB@A: 
A. Usaha pada Berbagai Proses Termodinamika 
1. Usaha yang Dilakukan Gas 
-:?;2E=29 C63E29 C:CD6 H2?8 5:=6?82A: 56?82? C63E29 D23E?8 52? 
A6?8:C2A 82C H2?8 52A2D 36B86B2 3632C C6A6BD: D2A2 A252 .#2 	 
.C292H2?85:=2E2?@=6982CC69E3E?82?56?82?A6BE3292?F@=E6 
82C252=29C63282:36B:ED#:2D62?2?82C366B;2A252A6?8:C2A6E5:2? 
A6?8:C2A 36B86C6B C6;2E9 . 6 2D2C 56?82? =E2C A6?2A2?8 A6?8:C2A 	 
EC292  H2?8 5:=2E2? @=69 C:CD6 82C D6B9252A =:?8E?82? 252=29 
5GQ5.  ,	 .  ,	 .  , 1 
,2D4!8


)2 
.?DEAB@C6C52B:6
EC2926B;2H2?85:=2E2?@=6982C252=29 
ekspansi W  0 
luas = W 
V 
2 
1 
180 Mudah dan Aktif Belajar Fisika untuk Kelas XI
,  O 
 
 
,
O,  O
$6D6B2?82? 
  EC292 H2?8 5:=2E2? C:CD6 82C 
,  D62?2? 82C @?CD2? 
  F@=E6 2G2=
F@=E6 29:B 
23./ 9
 36B=2E 92?H2 ;:2 D62?2? , @?CD2? ,6=22 
A6BE3292?F@=E6D6BC63EDEC29252A2D36B?:=2:A@C:D:72D2E?682D:7 
56?82? 6D6?DE2? C63282: 36B:ED 
 #:2 82C 6=2E2? 6CA2?C: A6?8632?82? EC292  36B?:=2: 
A@C:D:7 ,:CD6 6=2E2? EC292 H2?8 6?H63232? F@=E6?H2 
36BD2329
#:2 82C 5:2A2D2?  36B?:=2: ?682D:7 )252 C:CD6 D6BC63ED 
5:=2E2? EC292 @=69 =:?8E?82? H2?8 6?H63232? F@=E6?H2 
36BEB2?8
.C292 H2?8 5:=2E2? A252 C:CD6 5:C63ED 0.$ (0- %E2C 2B62 5: 
32G29 EBF2 252=29 EC292 H2?8 5:=2E2? @=69 C:CD6 )6B92D:2? 
.#2 
 
Gambar 8.1 
Sistem melakukan usaha 
terhadap lingkungannya. 
,E2DE82C52=2C:=:?56BD6BDEDEA6?82=2:AB@C6CC6A6BD: 
D2A2A2528232B-6?DE2?EC292H2?85:=2E2? 
@=6982CA252 
2 AB@C6C	
 
3 AB@C6C
 
4 AB@C6C	52? 
5 C6=EBE9AB@C6CD@D2= 
Gambar 8.2 
(a) Usaha yang dilakukan 
oleh sistem adalah 
positif (W = pV ). 
(b) Usaha yang dilakukan 
oleh sistem adalah 
negatif (W = –pV ). 
p 
V1 V2 
pemampatan W  0 
luas = W 
V1 V2 
V 
p 
2 
1 
ds 
F = pA 
2 
3 p(kPa) 
A B 
C 
E V(L) 
250 
50 
D 
25 75 
 6?82A286=2CD:A:CH2?83:2C2?H25:8E?22?E?DE 
:?E6C3:C2A64296D:25::C:2:BA2?2C
6?82?3292C2C6?5:B:;6=2C2?42B26B;2D6B@C 
C69:?8822:B3:C2D6D2AA2?2C 
Contoh 8.1
Termodinamika 181 
7# 
2 .C29252B:	6
C2256?82?=E2C
52?36B?:=2:A@C:D:72B6?22B29 
AB@C6C62?2? 
=E2C
P
%O
%
)2 

%
P

)2
# 
3 .C29252B:
6C2256?82?=E2C
52?36BD2?52?682D:72B6?22B29 
2. Usaha pada Proses yang Dialami Gas 
 2C H2?8 36B252 52=2 BE2?8 D6BDEDEA 52A2D 5:E329 62522??H2 
6=2=E: 3636B2A2 AB@C6C H2:DE AB@C6C :C@D6B2= AB@C6C :C@9@B: AB@C6C 
:C@32B: 52? AB@C6C 25:232D: 
a. Proses Isotermal 
)B@C6C :C@D6B2= 252=29 AB@C6C A6BE3292? 62522? C:CD6 A252 CE9E 
D6D2A .#2  )B@C6C D6BC63ED C6CE2: 56?82? !EE @H=6 H2:DE , 
@?CD2?-:?;2E=29A6BC222?82C:562=,*(=692B6?2CE9E 
*52?D6D2A22 
,,
O
 
.C292H2?85:=2E2?C:CD652A2D5:D6?DE2?6?88E?22?A6BC222? 
36B:ED 
   , 56?82?, 
*   
 
  
*   
 
  
':=2:*52?@?CD2?C69:?88252A2D5:6=E2B2?52B:A6BC222?:?D68B2= 
 *   
  
 
*
=? 
1 
1 
 
* =?O=? 
#25: EC292 H2?8 5:=2E2? @=69 C:CD6 A252 AB@C6C :C@D6B2= 252=29 
 
 O 
* =?
AB@C6C6:B: 
 =E2C
O
O
)2
)2%O
%O# 
4 .C29252B:	C2256?82??@=2B6?2	D:52636?DE3:52?856?82? 
CE3E=E2C?H2
 
5 .C2926C6=EBE92?AB@C6C252=29
O


## 
.C292D@D2=52A2D;E825:9:DE?8C642B2=2?8CE?8 
D@D2= =E2C
)2O
)2%O
%# 
p 
p1 
Gambar 8.3 
Kurva p–V dengan T konstan 
pada proses isotermal. 
V 
V1 V2 
p2 
Contoh 8.2 
E2@=82C2B8@?6E2:C642B2:C@D6B2=A252CE9E
L52B:F@=E62G2=
6?;25:


-6?DE2?EC292H2?85:=2E2?82CD6BC63ED
#	@=$ 
7# 
:6D29E: 
*
@= 
/@=E62G2=
/@=E629:B
b. Proses Isokhorik 
)B@C6C :C@9@B: 252=29 AB@C6C A6BE3292? 62522? C:CD6 A252 F@=E6 
D6D2A .#2
-:?;2E=29 632=: A6BC222? 62522? 82C :562= 
,  * F@=E6  D6D2A 
p 
p1 
p2 
V 
V1 = V2 
Proses isokhorik pada grafik p–V. 
p(Pa) 
Gambar 8.4 
V(L) 
V1 V2 
, 
 
, 
 
182 Mudah dan Aktif Belajar Fisika untuk Kelas XI 
, 
 
  
*  
 
 E?DE 82C :562= 56?82? * 52?  
C6=2=E D6D2A :32D?H2 
, 
 
  @?CD2? 2D2E 
, 
 
 
 
,

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