System, boundary

Files containing easy information about essential of physical

1. Medical physics (theoretical)
second lecture
System, Boundary and Surroundings
Dr. NOOR H. AYSA
2022

2. System, Boundary and Surroundings
STATEMENTSOFSECONDLAWOFTHERMODYNAMICS
ThesecondlawofthermodynamicshasbeenenunciatedmeticulouslybyClausius,
KelvinandPlanckinslightlydifferentwordsalthoughbothstatementsarebasically
identical.Eachstatementisbasedonanirreversibleprocess.Thefirstconsiders
transformationofheatbetweentwothermalreservoirswhilethesecondconsidersthe
transformationofheatintowork.
ClausiusStatement
“Itisimpossibleforaselfactingmachineworkinginacyclicprocessunaidedbyany
externalagency,totransferheatfromabodyatalowertemperaturetoabodyata
highertemperature”.Inotherwords,heatof,itself,cannotflowfromacoldertoahotter
body.
Kelvin-PlanckStatement
“Itisimpossibletoconstructanengine,whichwhileoperatinginacycleproducesno
othereffectexcepttoextractheatfromasinglereservoiranddoequivalentamountof
work”.AlthoughtheClausiusandKelvin-Planckstatementsappeartobedifferent,they
arereallyequivalentinthesensethataviolationofeitherstatementimpliesviolationof
other.

3. ClosedSystemIftheboundaryofthesystemisimpervioustothe
flowofmatter,itiscalledaclosedsystem.Anexampleofthissystemis
massofgasorvaporcontainedinanenginecylinder,theboundaryof
whichisdrawnbythecylinderwalls,thecylinderheadandpiston
crown.Heretheboundaryiscontinuousandnomattermayenteror
leave.OpenSystemAnopensystemisoneinwhichmatterflowsinto
oroutofthesystem.Mostoftheengineeringsystemsareopen.
IsolatedSystemAnisolatedsystemisthatsystemwhichexchanges
neitherenergynormatterwithanyothersystemorwithenvironment.
AdiabaticSystemAnadiabaticsystemisonewhichisthermally
insulatedfromitssurroundings.Itcan,however,exchangeworkwith
itssurroundings.Ifitdoesnot,itbecomesanisolatedsystem.

5. Phase.Aphaseisaquantityofmatterwhichishomogeneous
throughoutinchemicalcompositionandphysicalstructure.
HomogeneousSystem
Asystemwhichconsistsofasinglephaseistermedas
homogeneoussystem.Examples:Mixtureofairandwater
vapour,waterplusnitricacidandoctaneplusheptane.
HeterogeneousSystem
Asystemwhichconsistsoftwoormorephasesiscalleda
heterogeneoussystem.Examples:Waterplussteam,iceplus
waterandwaterplusoil.

6. MACROSCOPIC AND MICROSCOPIC POINTS OF VIEW
Thermodynamicstudiesareundertakenbythefollowingtwodifferentapproaches.1.
Macroscopicapproach—(Macromeanbigortotal)
2.Microscopicapproach—(Micromeanssmall)
THERMODYNAMIC EQUILIBRIUM
Asystemisinthermodynamicequilibriumifthetemperatureandpressureatall
pointsaresame;thereshouldbenovelocitygradient;thechemicalequilibriumis
alsonecessary.
Systemsundertemperatureandpressureequilibriumbutnotunderchemical
equilibriumaresometimessaidtobeinmetastableequilibriumconditions.Itisonly
underthermodynamicequilibriumconditionsthatthepropertiesofasystemcanbe
fixed.Thusforattainingastateofthermodynamicequilibriumthefollowingthree
typesofequilibriumstatesmustbeachieved:

7. 1.Thermalequilibrium.Thetemperatureofthe
systemdoesnotchangewithtimeandhassame
valueatallpointsofthesystem
2.Mechanicalequilibrium.Therearenounbalanced
forceswithinthesystemorbetweenthesurroundings.The
pressureinthesystemissameatallpointsanddoesnot
changewithrespecttotime.
3.Chemicalequilibrium.Nochemicalreactiontakes
placeinthesystemandthechemicalcompositionwhichis
samethroughoutthesystemdoesnotvarywithtime.

8. PROPERTIESOFSYSTEMS
Apropertyofasystemisacharacteristicofthesystemwhich
dependsuponitsstate,butnotuponhowthestateisreached.
Therearetwosortsofproperty:
1.Intensiveproperties.Thesepropertiesdonotdependonthemass
ofthesystem.Examples:Temperatureandpressure.
2.Extensiveproperties.Thesepropertiesdependonthemassofthe
system.Example:Volume.Extensivepropertiesareoftendividedby
massassociatedwiththemtoobtaintheintensiveproperties.For
example,ifthevolumeofasystemofmassmisV,thenthespecific
volumeofmatterwithinthesystemisV/m=vwhichisanintensive
property

9. CYCLE
Anyprocessorseriesofprocesseswhoseendstatesareidenticalis
termedacycle.Theprocessesthroughwhichthesystemhaspassed
canbeshownonastatediagram,butacompletesectionofthepath
requiresinadditionastatementoftheheatandworkcrossingthe
boundaryofthesystem.
IdealGasFromexperimentalobservationsithasbeenestablished
thatanidealgas(toagoodapproximation)behavesaccordingto
thesimpleequationpV=mRT
wherep,VandTarethepressure,volumeandtemperatureofgashavingmass
mandRisaconstantforthegasknownasitsgasconstant.Eqn.canbewritten
as pv=RT(wherev=V/m)

10. Inrealitythereisnogaswhichcanbequalifiedasanidealor
perfectgas.Howeverallgasestendtoidealorperfectgasbehaviour
atalltemperaturesastheirpressureapproacheszeropressure.
Fortwostatesofthegas,Eq.Abovecanbewrittenas
P
1V1/T
1=P
2V
2/T
2
T
2/T
1=( P
2/P
1 ) ( V
2/V
1 )
Example:Afluidatapressureof3bar,andwithspecificvolumeof
0.18m3/kg,containedinacylinderbehindapistonexpandsreversibly
toapressureof0.6baraccordingtoalaw,p=
!
"²
whereCisa
constant.Calculatetheworkdonebythefluidonthepiston