11.fisika1-kalor_kinetik

Fisika Panas

x

z

Thermal Physics

biological

processes

Phase

transitions

chemical reactions

Fabrication

of materials

generating work

semiconductors

Thermal radiation

(global warming)

magnetism

What rules describe the

behavior of:

Materials gases

liquids

solids

polymers

Phenomena thermal conduction

thermal radiation

heat engines

magnetism

•Temperatur

•Hk. Thermodinamika ke-0

•Thermometer & Skala Temperatur

•Pemuaian

•Gas Ideal

•Teori Kinetika Gas

Topics

Temperature and the zeroth Law of Thermodynamics

Two objects placed in thermal contact will eventually come to

the same temperature. When they do, we say they are in

thermal equilibrium.

A B

C

Then A and B are in thermal equilibrium.

If A is in thermal equilibrium with C

and B is in thermal equilibrium with C

The Zeroth Law of Thermodynamics

Thermometers and Temperature Scales

Temperature is a measure of how hot or cold something is.

Thermometers are instruments designed to measure

temperature. In order to do this, they take advantage of

some property of matter that changes with temperature.

Most materials expand when heated.

6

Termometer Galileo Tabung berisi cairan yang mudah

memuai (koefisien muai termalnya besar)

Bola-bola kecil berisi aneka cairan, dengan bermassa jenis dari besar sampai kecil

Jika suhu naik, makin banyak bola kecil tenggelam

Suhu ditunjukkan oleh bola yang terapung terendah

Common thermometers used today include the liquid-in-glass

type and the bimetallic strip.


Thermal Physics 10-01

A bimetallic strip, consisting of metal G on the top and

metal H on the bottom, is rigidly attached to a wall at the

left as shown. In the diagram. The coefficient of linear

thermal expansion for metal G is greater than that of

metal H. If the strip is uniformly heated, it will

(A) curve upward.

(B) curve downward.

(C) remain horizontal, but get longer.

(D) bend in the middle.

Temperature is generally measured using either the Kelvin,

Celsius, or the Fahrenheit scale.


Thermal Expansion of Solids and Liquids

A steel washer

is heated

Does the hole increase

or decrease in size?

Expansion occurs when an

object is heated.

When the washer

is heated

The hole

becomes

larger



Consider a flat steel plate with a hole through its center

as shown in the diagram. When the plate's temperature

is increased, the hole will

(A) expand only if it takes up more than half

the plate's surface area.

(B) contract if it takes up less than half

the plate's surface area.

(C) always contract.

(D) always expand.

Lo DL

DL LoDT

DT

DL = aLoDT

L = Lo(1+aDT)

Coefficient of

linear expansion

L - Lo = aLoDT


A cylindrical brass sleeve is to be shrunk-fitted over a

brass shaft whose diameter is 3.212 cm at 0 oC. The

diameter of the sleeve is 3.196 cm at 0 oC.

D d

To what temperature must the sleeve be heated before

it will slip over the shaft?

shaft sleeve

Thermal Expansion of Solids and Liquids (Problem)

To what temperature must the sleeve be

heated before it will slip over the shaft?

shaft sleeve

D d

C/1 10 x 19 o6-a

TLL iDaD

d

dDTf

a

-

C0T

cm 196.3d

cm 212.3D

oi

cm 3.196C/1 10x 19

cm 3.196cm 3.212

o6-

- C 263 o

dDL -D

if TTddD -a-

fdTdD a-


32o

2o

3o LLL3LL3LV DDD

New Volume

3o LLV D

Initial Volume

3oo LV

TL3V3oDaD

Lo

Lo

Lo

Lo + DL

Lo + DL

Lo + DL Volume Expansion

DL = aLoDT

LL3VVV2oo D-D

TLL3V o2o DaD

TV3V oDaD


TV3V oDaD

a 3

TVV oDD

TVVV oo D-

T1VV o D

Coefficient

of

Volume

Expansion


An automobile fuel tank is filled to the brim with 45 L of

gasoline at 10 oC. Immediately afterward, the vehicle is parked

in the Sun, where the temperature is 35 oC. How much gasoline

overflows from the tank as a result of expansion?

SG VVV D-DD

TVV oSG D-D

2545 10 x 3310 x 6.9 V64 -- -D

L 04.1V D

Overflow

Change in

volume

of the

gasoline

Change in

volume

of the steel

gas tank

TVTVV oSoG D-DD


Po

ten

tia

l E

ner

gy

Intermolecular Distance

Low Temperature

High Temperature


Thermal

Expansion

of Water

As the temperature of water decreases from 4ºC to 0ºC, it expands and its density decreases

Above 4ºC, water expands with increasing temperature, typical of other liquids and materials

Maximum density of water is 1000 kg/m3 at 4ºC

This unusual behavior explains why: ice humps up in the middle of the compartments in an ice cube tray

a lake freezes slowly from the top down (important for animal and plant life!)

water pipes can burst in the winter

PV = nRT

Pressure

(Pa)

Volume

(m3)

Absolute

Temperature

(K)

Gas Constant

(8.31 J/molK)

0.0821 (L.atm)/(mol.K)

1.99 cal/(mol.K)

Gas Quantity

(mol)

Microscopic Description of an Ideal Gas


~M1 ~M2 ~M3 ~M4 ~M5 ~M6 ~M7 ~M8 ~M10 ~M9 ~M11 ~M12 ~M13 ~M14 ~M15 ~M16 ~M17 ~M18 ~M20 ~M19 ~M21 ~M22 ~M23 ~M24 ~M25 ~M26 ~M27 ~M28 ~M30 ~M29 ~M31 ~M32 ~M33 ~M34 ~M35 ~M36 ~M37 ~M38 ~M40 ~M39 ~M41 ~M42 ~M43 ~M44 ~M45 ~M46 ~M47 ~M48 ~M50 ~M49 ~M51 ~M52 ~M53 ~M54 ~M55 ~M56 ~M57 ~M58 ~M60 ~M59

Both the pressure and volume of a given sample of

an ideal gas double. This means that its

temperature in Kelvin must

(A) double.

(B) quadruple.

(C) reduce to one-fourth its original value.

(D) remain unchanged.

A mole (mol) is defined as the number of grams of a substance

that is numerically equal to the molecular mass of the substance:

1 mol H2 has a mass of 2 g

1 mol Ne has a mass of 20 g

1 mol CO2 has a mass of 44 g

mol/g mass molecular

grams massmol n

Μ

mn

mol/particlesnumber svogadro'A

)(particles moleculesmol n

AN

Nn

The number of moles in a certain number of particles:

The number of moles in a certain mass of material:


PV = NkT

Pressure

(Pa)

Volume

(m3)

Absolute

Temperature

(K)

Boltzmann’s

Constant

(1.38 x 10-23 J/K)

Number of

Molecules


Boltzmann’s Constant

nRTPV NkT

N

nRk

nN

Rk

Gas

Constant

Avogadro’s

Number


A gas is contained in an 8.0 x 10-3 m3 vessel at 20 oC

and a pressure of 9.0 x 105 N/m2.

(a) Determine the number of moles of gas in the vessel.

nRTPV

RT

PVn

K 293Kmol/J 31.8

m10 x 0.8N/m 10 x 0.92325

-

mol 0.3n

Microscopic Description of an Ideal Gas (Problem)

A gas is contained in an 8.0 x 10-3 m3 vessel at 20 oC

and a pressure of 9.0 x 105 N/m2.

(b) How many molecules are in the vessel?

AnNN

mol 0.3n

mol

molecules23 10 x 02.6mol 0.3

molecules 10 x 8.1N24

Microscopic Description of an Ideal Gas (Problem (con’t))


A container of an ideal gas at 1 atm is compressed to

one-third its volume, with the temperature held

constant. What is its final pressure?

(A) 1/3 atm

(B) 1 atm

(C) 3 atm

(D) 9 atm

A cylinder with a moveable

piston contains gas at a

temperature of 27 oC, a volume

of 1.5 m3, and an absolute

pressure of 0.20 x 105 Pa. 1.5 m3 27 oC

0.20 x 105 Pa

0.70 m3

0.80 x 105 Pa


What will be its final temperature

if the gas is compressed to 0.70 m3

and the absolute pressure increases

to 0.80 x 105 Pa? 1.5 m3 27 oC

0.20 x 105 Pa

0.70 m3

0.80 x 105 Pa

nRTPV constantnRT

PV

i

ii

f

ff

T

VP

T

VP

ii

ffif

VP

VPTT

35

35

m 5.1 Pa 10 x 2.0

m 7.0 Pa 10 x 8.0K 300 K 560

273-

C 287o

Microscopic Description of an Ideal Gas (Problem)

K 300C 27o

The Kinetic Theory of Gases

Assumptions of kinetic theory:

2) molecules are far apart, on average

1) large number of molecules, moving in

random directions with a variety of speeds

3) molecules obey laws of classical mechanics and

interact only when colliding

4) collisions are perfectly elastic

x

y

z

v

L

A The force exerted on the wall by the collision

of one molecule of mass m is

tΔ

mvΔF

x

x

vL2

mv2

L

mv2x

Then the average force due to N

molecules colliding with that wall is

2xvN

L

mF


The averages of the squares of the speeds

in all three directions are equal:

So the pressure on the wall is:

A

FP

AL

vNm 2

31

V

vNm 2

31

L

vmNF

2

31

x

y

z

v

L

A

2xvN

L

mF


Rewriting,

so

The average translational kinetic energy of the molecules

in an ideal gas is directly proportional to the temperature

of the gas.

221

32 vm NPV NkT

kTvm 221

32

kTvmEK 232

21

V

vNmP

2

31


Molecular Kinetic Energy

Temperature is a measure of the average

molecular kinetic energy.

2

kT3KE

m

kT3v rms

2

vm 2

2

kT3

2

vm 2



According to the ideal gas Law, PV = constant for a

given temperature. As a result, an increase in volume

corresponds to a decrease in pressure. This happens

because the molecules

(A) collide with each other more frequently.

(B) move slower on the average.

(C) strike the container wall less often.

(D) transfer less energy to the walls of the container

each time they strike it.


The absolute temperature of an ideal gas is directly

proportional to which of the following?

(A) speed

(B) momentum

(C) kinetic energy

(D) mass


Oxygen molecules are 16 times more massive than hydrogen

molecules. At a given temperature, the average molecular

kinetic energy of oxygen, compared to hydrogen

(A) is greater.

(B) is less.

(C) is the same.

(D) cannot be determined since pressure and

volume are not given

What is the total random kinetic energy of all the

molecules in one mole of hydrogen at a temperature

of 300 K.

kT

2

3NK A

Avogadro’s

number

Kinetic energy

per molecule

J 3740K

K 003 K

J 10 x 38.1

2

3 molecules 10 x 02.6K

2323 -

The Kinetic Theory of Gases (Problem)

Calculate the rms speed of a Nitrogen molecule (N2)

when the temperature is 100 oC.

Mass of N2 molecule:

kg 10 x .65426-

kg 10 x .654

K 373 J/K 10 x .3813

26

23

-

-

m

kT3v rms

m/s 576v rms

rms speed:

molemolecules/ 10 x .026

kg/mole 10 x 0.28m

23

3-


If 2.0 mol of an ideal gas are confined to a 5.0 L vessel at

a pressure of 8.0 x 105 Pa, what is the average kinetic

energy of a gas molecule?

Temperature of the gas:

nRTPV

nR

PV T

-

Kmol

J31.8mol 0.2

m 10 x 0.5Pa 10 x 0.8

335

K 442

Kinetic energy:

kT2

3K K 244

K

J 10 x 38.1

2

3 23

-

molecule

J 10 x 38.1 23-



A container holds N molecules of an ideal gas at a given

temperature. If the number of molecules in the container is

increased to 2N with no change in temperature or volume,

the pressure in the container

(A) doubles.

(B) remains constant.

(C) is cut in half.

(D) none of the above

Mean and rms Speed 5

2

3

6 2

6

1

4 Mean Speed:

8

52362461

8

5236246122222222

rms Speed:

m/s 4.0v rms

m/s 3.6v mean



A sample of an ideal gas is slowly compressed to one-half

its original volume with no change in temperature. What

happens to the average speed of the molecules in the

sample?

(A) It does not change.

(B) It doubles.

(C) It halves.

(D) none of the above


A mole of diatomic oxygen molecules and a mole

of diatomic nitrogen molecules at STP have

(A) the same average molecular speeds.

(B) the same number of molecules.

(C) the same diffusion rates.

(D) all of the above

Summary

Temperature is a measure of how hot or cold something is,

and is measured by thermometers.

There are three temperature scales in use: Celsius,

Fahrenheit, and Kelvin.

When heated, a solid will get longer by a fraction given

by the coefficient of linear expansion.

The fractional change in volume of gases, liquids, and

solids is given by the coefficient of volume expansion.

nRTPV Ideal gas law:

One mole of a substance is the number of grams equal to

the atomic or molecular mass.

Each mole contains Avogadro’s number of atoms or molecules.

The average kinetic energy of molecules in a gas is

proportional to the temperature:

kTvmEK 232

21

Summary

11.fisika1-kalor_kinetik

Documents

thermal equilibrium

temperature scales temperature

thermal contact

liquids thermal physics

plates temperature

shaft sleeve d d c1

d bend

b curve