Post on 31-Dec-2015
description
transcript
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