HW

1
HW 15 Thermodynamics

• READ CHAPT 12 13
• C 12
• 5,7,8,10,11,21,25
• C 13
• 14,16,20
• handout questions

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THERMODYNAMICS

• The study of utilizing heat energy to do work

3
FORMS OF ENERGY

• HEAT
• INTERNAL ENERGY
• WORK

4
HEAT

• Energy transferred during the random collisions
  of particles
• LOWEST FORM OF ENERGY
• Highest Entropy Level
• Disorganized, Difficult to Harness

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INTERNAL ENERGY (U)

• Energy contained by particles of system due to
  their random motion
• collective kinetic energy

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INTERNAL ENERGY (U)
KE 3/2 kBT
kB R/Na
kB Boltzmans Constant
U N (KE)
N total particles
U N (3/2 kBT)
U N (3/2 R/NAT)
U N/Na (3/2 RT)
N/Na moles n
U (3/2 nRT)
DU (3/2 nRDT)
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INTERNAL ENERGY (U)

• U 3/2 nRT
• R Universal gas law constant
• R 8.31 J/mole K
• U a NUMBER OF MOLES (n)
• U a TEMPERATURE (T)
• DU 3/2 nRDT

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HEAT ENGINE

• CONVERTS HEAT ENERGY INTO WORK

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WORK

• FORCE X DISTANCE (F x d W)

CYLINDER
d
PISTON
SYSTEM
F
(See IP simulation)
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LAWS OF THERMODYNAMICS

• ZEROTH
• FIRST
• SECOND

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Zeroth Law

• IF TWO SYSTEMS AT SAME TEMP
• THEN NO HEAT WILL FLOW
• HEAT FLOWS FROM HOT TO COLD

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THERMODYNAMIC INTERACTIONS

• HEAT (Q) CAN BE
• GAINED ()
• LOST (-)
• WORK (W) CAN BE
• DONE ON SYSTEM ()
• DONE BY SYSTEM (-)

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THERMODYNAMIC INTERACTIONS
HEAT input
Q
HEAT output
-Q
system
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WORK INPUT OR OUTPUT
WORK DONE BY -W
WORK DONE ON W
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FIRST LAW OF THERMO
DU Q W

• Q DU (- W)
• HEAT D INTERN ENERGY WORK
• CONSERVATION OF ENERGY

HEAT Q
CHANGE INTERNAL ENERGY DU
WORK(-W)
SYSTEM
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State of the System

• Pressure (P)
• P Force/Area
• N/m2 Pa (Pascals)
• Temperature (T)
• Kelvin (absolute)
• Volume (V)
• cubic meters (m3)

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HEAT ENGINE CYCLE

• A SERIES OF PROCESSES WHICH ENABLE A SYSTEM TO DO
  WORK
• SYSTEM RETURNS TO THE ORIGINAL STATE
• CYCLE
• P , V, T

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ISOBARIC PROCESS
PRESSURE constant
PRESSURE FORCE/AREA
P F/A
A d DV
F P A
d
WORK F d
WORK P A d
F
WORK PDV
Q
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P - V DIAGRAMISOBARIC PROCESS (P constant)
2
1
P1
W P DV
WORK AREA
P
W is -
DV
V
V1
V2
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ISOMETRIC PROCESS
VOLUME constant
WORK PDV
DV0
WORK 0
DU Q W
Q IN
DU Q
Cv molar Specific heat
DU Q ncvDT
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P - V DIAGRAMISOMETRIC PROCESS (V constant)
DV 0
W P DV
P2
2
WORK AREA 0
P
DU Q W
System gets hotter!!
Q DU
1
P1
V
V1
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ISOTHERMAL PROCESS
TEMPERATURE constant
DU 3/2 nRDT
system expands
DU 0
DU Q W
DT 0
Q IN
system
Q -W
ALL HEAT CONVERTED TO WORK
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P - V DIAGRAMISOTHERMAL PROCESS (T constant)
1
Q -W
P1
Q
P
2
P2
isotherm
AREA WORK
V
V1
V2
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ADIABATIC PROCESS
NO HEAT EXCHANGED
Q 0
DU Q W
SYSTEM EXPANDS
DU W
SYSTEM DOES WORK
Q0
System cools down
system
System gives up energy
WORK FROM INTERNAL ENERGY
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P - V DIAGRAMADIABATIC PROCESS (Q 0)
DU Q W
1
P1
WDU
DU W
P
isotherm
T hot
2
P2
T cold
AREAWORK
V
V1
V2
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Heat Engine Schematic
Hot Reservoir Thot
Q in
Engine cylinder
WORK
Q out
Cold Reservoir Tcold
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Heat Engine Efficiency
Q in Work Q out
Work Q in - Q out
Conservation of Energy
Efficiency Work / Q in
Q in - Q out
Eff W
Q in
Q in
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Heat Engine Cycle P-V Diagram
1,2 isobaric 2,3 isometric 3,4 isobaric 4,1
isometric
2
Q in
1
P
area enclosed net work
work 1,2 -
Q out
Q in
3
4
work 3,4
Q out
V
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Real Engine Cycle Otto 2-Cycle
1,2 adiabatic compression
FUEL AIR MIX
3
1,2 adiabatic 2,3 isometric 3,4 adiabatic 4,1
isometric
2,3 isometric (ignition)
Q in
4
P
2
3,4 adiabatic (power stroke)
Q out
1
V
4,1 isometric (exhaust)
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Carnot Engine CycleIdeal Engine

• No engine operating between two temps can do
  better than Carnot
• For a Carnot cycle (ONLY!)

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Carnot Cycle
Isothermal Expansion Adiabatic Expansion Isotherma
l Compression Adiabatic Compression
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Carnot CycleIdeal Engine Cycle
1
Q in
2
P
T hot
4
isotherm
Q out
T cold
3
V
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Entropy (S)

• randomness, disorder

DS Q/T
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Carnot Engine Cycle T-S Diagram
1,2 isothermal 2,3 adiabatic 3,4 isothermal 4,1
adiabatic
2
Q in
1
T Hot
Qin - Qout net W
HEAT 1,2 Q
T
DS Q/T
3
4
T Cold
HEAT 3,4 -Q
Adiabatic Q 0 DS 0
Q out
Entropy (S)
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Reverse Heat Engine
Heat Engine Goal
Reverse Heat Engine Goal
Work done to Pump Heat uphill
Q
Hot
Cold
REFRIDGERATOR!!!
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Reverse Heat Engine Schematic
Refridgeration Cycle
Hot Reservoir Thot
Q in
Engine cylinder
WORK
Q out
Cold Reservoir Tcold
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Reverse Carnot CycleIdeal Refridgeration Cycle
3
Q out
2
P
T hot
4
isotherm
Q in
T cold
1
V
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Molecular Model for an Ideal Gas

• http//fiscom.fcfm.buap.mx/ntnujava/

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Carnot web sites

• www.phy.ntnu.edu.tw/java/carnot/carnot.html