chapter 7 temperature and zeroth law new

8/16/2019 Chapter 7 Temperature and Zeroth Law New

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Fundamental Physics

Chapter 7

PETROVIETNAM UNIVERSITY

FACULTY OF FUNDAMENTAL SCENCES

Hanoi, August 2012

Pham Hong QuangE-mail: [email protected]


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Chapter 7 Temperature, Heat, and the Frst Lawof Thermodynamics

Pham Hong Quang Faculty of Fundamental Sciences 2

7.1 Temperature and Zeroth law of

Thermodynamics

7.2 Thermal Expansion

7. The !irst "aw of Thermodynamics

7.# Thermodynamic Processes

7.$ Heat Transfer


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7.1 Temperature and Zeroth law of Thermodynamics


The standard scale of temperature is Kelvin.

The Kelvin scale is setup so that its zero point is

the coldest possible temperature--absolute zero,

at which point a substance would have zero

internal energy. Absolute zero can never be

reached, but there is no limit to how close we can

get to it. Scientists have cooled substances to

within 1-!

Kelvins of absolute zero. "ow do we#now how cold absolute zero is, if nothing has

ever been at that temperature$ The answer is by

graphing %ressure vs. Temperature for a variety of

gases and e&trapolating.

Temperature measures the %speed& of the

molecules


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The zeroth law of thermodynamics:

•If two systems are each in thermal

equilibrium with a third, then they are in

thermal equilibrium with one another.

•'f two thermal systems are in thermal e(uilibrium

with one another, then they have the same

temperature.

• Temperature is the indicator of thermal e(uilibrium

in the sense that there is no net )ow of heat

between two systems in thermal contact that have

f


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't wor#s based on thevariation of pressure of a*&ed volume gas as its

temperature changes. The volume of the gas is#ept constant by raising orlowering the reservoir + to

#eep the mercury level at Aconstant. The pressure is indicatedby the height dierencebetween reservoir + and

column A.

'onstant ()olume

*as Thermometer

d hl f


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To *nd the temperature of a substance, the gas)as# is placed in thermal contact with thesubstance.

The thermometer readings are virtuallyindependent of the gas used.'f the lines for various gases are e&tended, thepressure is always zero when the temperature is

/0.1!o

. This temperature is called a+solute ,ero.Absolute zero is used as the basis of thea+solute temperature scale.

'onstant()olume *as Thermometer-

'ont.

d hl f


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Thermodynamics


How do you cali+rate yourthermometer

•+y international agreement the triple point of water

has been assigned the value of /0.12 K.

•elsius scale3 't means3 Tc at

the triple point is .1 elsius degree.

•4ahrenheit scale

T

F =

9

5T C + 32 = 32.02oF

=

→ 30lim16.273

p p K T

m

15.273−=T T c


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Thermodynamics



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Thermodynamics


Temperature Measurement -Some Thermometers


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The volume of matter

e&pands when the atomic

spacing increases.

'ncrease temperature

5 increase volume.

T V V ∆=∆ 0β


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•4or small volumechanges therelationship betweenvolume and

temperature is linear.

• The coe6cient ofvolume e&pansion isβ.

7aterial oe6cient β8uartz 1 & 1-2 °-1

%yre& glass 9 & 1-2 °-1

:lass / & 1-2 °-1

Steel 0! & 1-2 °-1

Aluminum /! & 1-2 °-1

7ercury 1; & 1-2 °-1

1 atm? 0@ & 1-2 °-1


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•7ost substancese&pand uniformlywith temperature.

•


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The change involume applies tothe threedimensions.

'f the change ise(ual in alldirections β is splitin thirds.

The coe6cient oflinear e&pansion insolids >α? is usually

one third of β.

W H L HW LW LH V

W H LV

∆+∆+∆≅∆

=

000000

0000

)3

(

)3

(

)3

(

000

000

000

W T H L

W H T L

W H LT V

β

β

β

∆+

∆+

∆≅∆

3/

0

β α

α

=∆=∆ LT L


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7.3 The First Law of Thermodynamics


Thermodynamics is the study of the inter-relation between heat, wor# and internalenergy of a system and its interaction with itsenvironment..

Thermodynamics

=&ample systems• :as in a container• 7agnetization and

demagnetization•

harging Bdischarging a battery

• hemical reactions• Thermocouple

operation


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Thermodynamics tates

A state /aria+le describes the stateof a system at time t, but it does notreveal how the system was put into

that state.=&amples of state variables3• % C pressure >%a or DEm?,• T C temperature >K?,•

C volume >m0

?,• n C number of moles, and• F C internal energy >G?.


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0hat is heat


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Specific Heats c at Room

Temperature

Substance Joules/kg/K

lead 128

copper 386

aluminum 900

glass 840

water 4190


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Heats of Transformation


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To vaporize a li(uid means to change it fromthe li(uid state to the vapor or gas state.

This process re(uires energy because themolecules must be freed from the li(uid state.ondensing a gas to a li(uid is the reverse of

vaporizing it re(uires that energy be removedfrom the gas so that the molecules can clustertogether instead of )ying away from eachother.

The heat of transformation for these phase

changes is called the heat of /apori,ation,Jv. vLmQ ⋅=


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The internal energy of a system changesfrom an initial value Ui to a nal value of

Uf due to heat Q and work W.

Q is positive when the system gains heat andnegative when it loses heat. W is positive

when wor# is done by the system andnegative when wor# is done on the system.


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!am"le $.

Positi/e and 4egati/e0or5


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7.4 Thermodynamic Processes


A thermodynamic process is represented by a

change in one or more of the thermodynamicvariables describing the system.

=ach point on the curverepresents ane(uilibrium state of thesystem.


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The area under apressure-volume graph isthe wor# for any #ind of

process. The colored area givesthe wor# done by the gasfor the process from X to

Y .

!"r# and the Area Under a Pressure$

%"lume &raph


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Chec# Y"ur Understandin'

74Thermodynam cProcesses


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7.4 Thermodynam c Processes


6n iso+aric process

is one that occurs at constant pressure.

4or an isobaricprocess, a pressure-versus-volume plot isa horizontal straight

line, and the wor#done LW C P>V f

V i?M is the colored

rectangular area

under the graph.

h d i


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The substance in thechamber is

e&pandingisobarically becausethe pressure is heldconstant by the

e&ternal atmosphereand the weight ofthe piston and thebloc#.

6n iso+aric process-

cont.

h d i


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Example 3.

s"(aric E)pansi"n "* !ater

Nne gram of water is placed in the cylinder in above

*gure, and the pressure is maintained at . O 1!

%a. The temperature of the water is raised by 01 P.'n one case, the water is in the li(uid phase and

e&pands by the small amount of 1. O 1; m0. 'n

another case, the water is in the gas phase and

e&pands by the much greater amount of /.1 O 1!

m0. 4or the water in each case, *nd >a? the wor#

done and >b? the change in the internal energy.

c # $%&' (!g*+)

c P # -- (!g*+).

74Th d iP


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>a?

>b?

74Th d iP


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sochoric process 8'sometric?

one that occurs at constant volume.

>a?The substance in the chamberis being heated isochoricallybecause the rigid chamber#eeps the volume constant.

>b?The pressure-volume plot foran isochoric process is avertical straight line. The area

under the graph is zero,indicating that no wor# isdone. 't means that thechange in the internal energye(uals the heat transfer3

QF C 8

74Th d iP


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There is adia+atic process, one that occurs

without the transfer of heat . Since there is no

heat transfer, Q e(uals zero, and the *rst law

indicates that C Q W C W . Thus,

when wor# is done by a system adiabatically,

W is positive and the internal energy of the

system decreases by e&actly the amount of

the wor# done.


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6dia+atic process-

cont.

74Th d iP


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isothermal process,one that ta#es place at

constant temperature. 'n

an isothermal process,

both % and of the gas

change

sothermal process

74Th d iP


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=== ∫ ∫

i

f

v

v

v

v v

vnRT

V

nRTdV PdV W

f

i

f

i

ln

Thermal Pr"cesses Usin' an deal &as+ E)ample

74Th d iP


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Two moles of the monatomic gas argon e&pandisothermally at 9; K, from an initial volume of V i

C .! m0 to a *nal volume of f C .! m0.

Assuming that argon is an ideal gas, *nd >a? thewor# done by the gas, >b? the change in theinternal energy of the gas, and >c? the heatsupplied to the gas.

Thermal Pr"cesses Usin' an deal &as


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75HeatTransferMechanism


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7.5 Heat Transfer Mechanism


Conduction


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7.5 Heat Transfer


Substance k (W/m . K)

Stainless steel 14

Aluminum 235

Copper 401

Polyurethane foam 0.024

Air 0.026

'onduction>Through solid slabs?

Q

t = kA(T

H − T

C )

L

%cond

C 8 E t

>energyEtime?

75HeatTransfer


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7.5 Heat Transfer


9ate through each sla+ are e:ual in

steady state

Pcond = k 1 A(T x − T C )

L1= k 2 A(T H − T x )

L2

Pcond = A(T H −T C )

L1

k 1+ L2

k 2

Pcond = A(T H − T C ) L1k 1

+ L2

k 2+ L3

k 3

75HeatTransfer


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7.5 Heat Transfer


'on/ection

'on/ection and ;uoyancy

- onvection occurs because when a )uid such

as air or water is heated its density

decreases.

- 't rises up through a buoyant force .

- The heated air from a candle )ame or hot

stove rises because of this.

- Ue(uires a medium

75HeatTransfer


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7.5 Heat Transfer


75HeatTransfer


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7.5 Heat Transfer


75HeatTransfer


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7.5 Heat Transfer


75HeatTransfer


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7.5 Heat Transfer


Emission experimenteperiment

75HeatTransfer


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7.5 Heat Transfer


Absorption experiment


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Thank you%

chapter 7 temperature and zeroth law new

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