10 Fisika Termal Bag 2 Nov 12 Revisi (1)

8/13/2019 10 Fisika Termal Bag 2 Nov 12 Revisi (1)

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FISIKA TERMALBAGIAN 2


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Ekspansi termal dari benda padat dan cair

Fenomena terjadinya peningkatan volume dari suatu materi

karena peningkatan temperatur disebut dengan ekspansi

termal.Ekspansi termal adalah konsekuensi dari perubahan average

separationantar atom dalam suatu materi.


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Benda akan memanjangbila temperaturnyameningkat

Pertambahan panjangproporsional terhadapperubahan temperaturDL/L = a DT atau

DL = a LDT atau

dL

dTaL

L DL

L DL

DL/L = aDT

DL/L = aDT

Ekspansi Linier


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Contoh:

Suatu penggaris besi dikalibrasi pada suhu 20 C. Hitungerror dalam pengukuran jika penggaris tersebut digunakan

untuk mengukur sepanjang 500 mm pada temperatur 45 C.

abesi= 1,2x10-5C-1

DL/L = aDT

DL = L a DT

DL = 500 x10-3m x 1,2 x10-5C-1 x 25 C

DL = 1,5x10-4m = 0,15 mm


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Ekspansi Volume

Setiap sisi panjang berubah dari Lmenjadi L+DL = L + La DT

Volume awal = L3

Volume baru (V+DV)

= (L +DL)3= (L + La DT)3

= (L (1+a DT))3

= L3

(1+ aDT)3

= V [1+3aDT+3(aDT)2 +(aDT)3]

L DL


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Ekspansi Volume (lanjutan)

V+DV = V [1+3aDT+3(aDT)2

+(aDT)3

]DV / V = [3aDT+3(aDT)2 +(aDT)3]

Karena aDT < 1 untuk nilai DT < 100 Cmaka nilai 3(aDT)2 dan (aDt )3dapat

diabaikan. Sehingga:DV / V = 3aDT

DV = 3a V DT

3a b DV = bV DT

L DL


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Unusual Behavior of Water

Cairan umumnya akan meningkat volumenya denganpeningkatan temperatur. Kecuali untuk air dingin sepertiditunjukkan pada gambar.


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Ideal Gas

An ideal gasis an idealized model for real gases that have

sufficiently low densities.

The condition of low density means that the molecules of the

gas are so far apart that they do not interact (except duringcollisions that are effectively elastic).

The ideal gas law expresses the relationship between the

absolute pressure (P), the Kelvintemperature (T), the

volume (V), and the number of moles (n) of the gas.


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Misal gas ideal didalam wadah silinder yang

volumenya dapat divariasikan dengan pistonyang dapat bergerak. Jika diasumsikan sistem

tertutup, maka massa (atau jumlah mol) gas

tetap konstan. Pada sistem tersebut dapat

diperoleh informasi:

Pada temperatur konstan, tekanan berbanding

terbalik dengan volume (Hukum Boyle)

Pada tekanan konstan, volume berbanding

lurus dengan temperatur (Hukum Charles)

Pada volume konstan, tekanan berbandinglurus dengan temperatur (Hukum Gay-Lussac)


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Amount of Gas

Better to describe gas in terms of number of moles.

The number of moles ncontained in any sample is the

number of particles Nin the sample divided by the

number of particles per mole NA(Avogadro's number):

AN

Nn

The number of moles contained in a sample can also be

found from its mass.

M

mn


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Avogadros Constant

One moleof any gas contains

the same number of particles.

This number is called

Avogadros constant and hasthe symbol NA. The value of

NAis 6.02 1023particles per

mole.


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Avogadros Law

nV

The most significant consequence of

Avogadro's law is that the ideal gas

constanthas the same value for all

gases. This means that the constant is

given by:-

constant

22

22

11

11 nT

Vp

nT

Vp


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Deriving Ideal Gas Equation

From Boyles Law:

From CharlessLaw:

From Avogadros Law:

Combining these three:

Rewriting using the gas

constant R:

pV

1

p

nTV

nV

TV

nRTpV

p

nTRV

Therefore:-


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PV Diagram in Thermodynamic Process


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Kinetic Theory of Gases

The pressurethat a gas

exerts is caused by the

impact of its molecules

on the walls of the

container.


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Consider a gas molecule colliding

elastically with the right wall of thecontainer and rebounding from it.

The force on the molecule is obtained

using Newtons second law as follows:

D

D

t

PF

( (

L

mv

vL

mvmvF

2

2


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The force on one of the molecule:

According to Newton's law of actionreaction, the force on

the wall is equal in magnitude to this value, but oppositely

directed.

The force exerted on the wall by one molecule:L

mv 2

( ( L

mv

vL

mvmv 2

2


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If N is the total number of molecules, since these particles

move randomly in three dimensions, one-third of them on theaverage strike the right wall. Therefore, the total force is:

Vrms = root-mean-square velocity.

L

vmNF rms

2

3


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Pressureis forceper unitarea, so the pressure Pacting on a

wall of area L2is

Since the volume of the box is V = L3, the equation above

can be written as

3

2

23 L

vmN

L

FP rms

2

2

1

3

2

rmsvmNPV


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Contoh soal:

1. Berapa banyaknya massa Cl2(gram) yang dapat

disimpan dalam suatu wadah (kontainer) dengan volume

10 L pada suhu 30 C dan tekanan 1000 kPa?

2. Pada suhu 150 C dan tekanan 100 kPa, sebuah

senyawa dengan massa 2,506 gram memiliki volume 1

L. Hitung massa molar senyawa tersebut.3. Berapa vrms dari atom helium yang mengisi sebuah

balon dengan diameter 30 cm pada suhu 20 Cdan

tekanan 1 atm?(diketahui jumlah atom helium dalam

balon sebanyak 3,54 x 1023

dan massa atom helium 6,64x 10-24g)


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TERIMAKASIH

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10 Fisika Termal Bag 2 Nov 12 Revisi (1)