Chapter19Chapter19

Temperature , Heat , and the Temperature , Heat , and the First Law of ThermodynamicsFirst Law of Thermodynamics

19-2 The Zeroth Law of Thermodynamics19-2 The Zeroth Law of Thermodynamics

If bodies A and B are each in thermal equilibrium with a third body T,then they are in thermal equilibrium with each other.

The zeroth law of thermodynamics:

19-3 Measuring Temperature19-3 Measuring TemperatureThe Triple Point of Water

erature)point temp-(triple 16.2733 KT

The Constant – Volume Gas Thermometer

CpT

ghpp 0

P is the pressure within the gas and C is a constant.

is the atmospheric pressure, is the density of the mercury in the manometer

33 CpT

is the gas pressure now

)lim)(16.273(3

0 p

pKT

gas

A temperature with a gas thermometer is

al)(provision ))(16.273()(33

3 p

pK

p

pTT

19-4 The Celsius and Fahrenheit Scales19-4 The Celsius and Fahrenheit Scales

00 95 FC

015.273TTC

0325

9 CF TT

FC 00 320

represents a Celsius temperature and T a Kelvin temperature

The relation between the Celsius and Fahrenheit scales is

Sample Problem 19-1Sample Problem 19-1

FFFT 1591910.32

ZZZ 0.84)0.98(0.14

F

Z

FZ 191

0.79

180)0.84(

19-5 Thermal Expansion19-5 Thermal Expansion

Linear ExpansionTLL

is a constant called the coefficient of linear expansion.

Volume ExpansionTVV

3Is the coefficient of volume expansion of the solid or liquid.

Sample Problem 19-2Sample Problem 19-2

L

LL

VVVdel

36190

80837000

L

KCL

TVV

808

)0.23)(/1050.9)(37000( 4

19-6 Temperature and Heat19-6 Temperature and Heat

Heat is the energy that is transferred between a system and its environment because of a temperature difference that exists between them.

JBtucal 1860.410969.31 3

Definition of heat:

19-7 The Absorption of Heat by 19-7 The Absorption of Heat by Solids and LiquidsSolids and Liquids

Heat Capacity)( if TTCTCQ

and are the initial and final temperatures of the object.

Specific Heat)( if TTcmTcmQ

KkgJFbBtuCgcalc /41901/1/1

Molar Specific Heatunits elementary 106.02 mol 1 23

Heats of TransformationThe amount of energy per unit mass that must be transferred as heat when a sample completely undergoes a phase change is called the heat of transformation L.

LmQ

The heat of vaporization

kgkJmolkJgcalLV /2256/7.40/539

kgkJmolkJgcalLF /333/01.6/5.79

The heat of fusion

Sample Problem 19-3Sample Problem 19-3(a)

Step 1kJJ

CCkgKkgJ

TTmcQ ifice

98.1515984

)]10(0)[720.0)(/2220(

)(1

kJJ

CCkgKkgJ

TTmcQ ifliq

25.4545252

)015)(720.0)(/4190(

)(3

kJkgkgkJmLQ F 8.239)720.0)(/333(2

kJ

kJkJkJ

QQQQtot

300

25.458.23998.15321

gkgkgkJ

kJ

L

Qm

F

rem 580583.0/333

194

Step 2

Step 3

(b)

ggg 140580720

Sample Problem 19-4Sample Problem 19-4

For the water:For the beaker:

For the copper:

)( ifwww TTmcQ

)( TTmcQ fccc

)( ifbb TTCQ

0 cbw QQQ0)()()( TTmcTTCTTmc fccifbifww

ccbww

iwwibccf mcCmc

TmcTCTmcT

19-8 A Closer Look at Heat and Work19-8 A Closer Look at Heat and WorkThe differential work dW done by the gas during the displacement is

f

i

V

VpdVdWW

pdVAdspdspAsdFdW

)())((

The gas to change its volume from Vi to Vf ,the total work done by the gas is

There are actually many ways to take the gas from state i to state f .

19-9 The First Law of Thermodynamics19-9 The First Law of Thermodynamics

The first law of thermodynamics:law)(first int,int,int WQEEE if

law)(first int dWdQdE

The internal energy Eint of a system tends to increase if energy is added as heat Q and tends to decrease if energy is lost as work W done by the system.

19-10 Some Special Cases of the 19-10 Some Special Cases of the First Law of ThermodynamicsFirst Law of Thermodynamics

The Law:

Process Restriction Consequence

Adiabatic Q=0 =-W

Constant volume W=0 =Q

Closed cycle =0 Q=W

Free expansion Q=W=0 =0

1.Adiabatic processes.

2. Constant - volume

3.Cyclical processes.

4.Free expansions.

WQ WE int

QE int0int E

Sample Problem 19-5Sample Problem 19-5

(a)

MJkJ

kJkJWQE

09.22090

1692256int

JJ

mmPa

VVpdVppdVW if

V

V

V

V

f

i

f

i

1691069.1

)1000.1671.1)(1001.1(

)(

5

3335

kJkJ

kgkgkJmLQ V

22602256

00.1)(/2256(

(b

)

(c)

19-11 Heat Transfer Mechanisms19-11 Heat Transfer MechanismsConduction

L

TTkA

t

QP CH

cond

The conduction rate

Thermal Resistance to Conduction (R-Value)

k

LR

Conduction Through a Composite Slab

1

1

2

2 )()(

L

TTAk

L

TTAkP CXXH

cond

1221

1221

LkLk

TLkTLkT HC

X

)/(

)(

kL

TTAp CH

cond

2211 //

)(

kLkL

TTAp CH

cond

Radiation

)( 44 TTAPPP envradabsnet

4ATPrad

4envabs ATP

Sample Problem 19-6Sample Problem 19-6

ddd

aaa L

TTAkP

L

TTAkP 5421 and

5214 )( TTTLk

LkT

ad

da

C

CCCLk

LkT

aa

aa

0.8

)10()2025()0.5(

)0.2(4

Sample Problem 19-7Sample Problem 19-7

t

EPrad

)()()( 41

42

41

42

1212

TTAttATtAT

tPtPEEE rr

232 10027.5)020.0(4 mmA

JKKs

mKmWE

8.406])308()320)[(1200(

)10027.5)(80.0)(/106703.5(44

23428

JJE

81.0500

8.406

500

KCCT 320273472

KCCT 308273351

REVIEW & SUMMARYREVIEW & SUMMARYThe Kelvin Temperature Scale

)lim)(16.273(3

0 p

pKT

gas

A temperature with a gas thermometer is

Celsius and Fahrenheit Scales

015.273TTC

0325

9 CF TT

represents a Celsius temperature and T a Kelvin temperature

The relation between the Celsius and Fahrenheit scales is

Thermal ExpansionTLL

is a constant called the coefficient of linear expansion.

TVV

3Is the coefficient of volume expansion of the solid or liquid.

HeatJBtucal 1860.410969.31 3

Heat Capacity and Specific Heat)( if TTCTCQ

and are the initial and final temperatures of the object.

)( if TTcmTcmQ

Where c is the specific heat of the material making up the object.

Heat of Transformation

LmQ

Work Associated with Volume Change

f

i

V

VpdVdWW

The gas to change its volume from Vi to Vf ,the total work done by the gas is

First Law of ThermodynamicsThe first law of thermodynamics:

law)(first int,int,int WQEEE if

Applications of the First Law1.Adiabatic processes.

2. Constant - volume

3.Cyclical processes.

4.Free expansions.

WQE , 0intWEQ int , 0

QEW int , 0 0int EWQ

law)(first int dWdQdE

Conduction , Convection , and Radiation

L

TTkA

t

QP CH

cond

The conduction rate

4ATPrad 4

envabs ATP