TTHERMODYNAMICS-IHERMODYNAMICS-I

INTRODUCTIONINTRODUCTIONTHERMODYNAMICS THERMODYNAMICS

=THERMO+DYNAMICS=THERMO+DYNAMICS

THERMO MEANS HEAT AND DYNAMICS THERMO MEANS HEAT AND DYNAMICS MEANS MOTION RESULTING INTO WORKMEANS MOTION RESULTING INTO WORK

THERMODYNAMICS IS THAT BRANCH OF THERMODYNAMICS IS THAT BRANCH OF SCIENCE WHICH DEALS WITH THE SCIENCE WHICH DEALS WITH THE

QUANTITATIVE RELATIONSHIP BETWEEN QUANTITATIVE RELATIONSHIP BETWEEN HEAT AND OTHER FORMS OF ENERGY.HEAT AND OTHER FORMS OF ENERGY.

OBJECTIVES OFOBJECTIVES OF THERMODYNAMICSTHERMODYNAMICS

TO PREDICT THE FEASIBILITY OF A TO PREDICT THE FEASIBILITY OF A PROCESS.PROCESS.

TO PREDICT THE YIELDS OF THE TO PREDICT THE YIELDS OF THE PRODUCTS.PRODUCTS.

TO DEDUCE SOME IMPORTANT TO DEDUCE SOME IMPORTANT GENERALISATIONS OF PHYSICAL GENERALISATIONS OF PHYSICAL CHEMISTRY.CHEMISTRY.

LIMITATIONS OF THERMODYNAMICSLIMITATIONS OF THERMODYNAMICS

IT HELPS TO PREDICT FEASIBILITY OF IT HELPS TO PREDICT FEASIBILITY OF SYSTEM ,DOES NOT TELL ABOUT THE TIME SYSTEM ,DOES NOT TELL ABOUT THE TIME TAKEN FOR PROCESSTAKEN FOR PROCESS

DEALS WITH ONLY MACROSCOPIC SYSTEM DEALS WITH ONLY MACROSCOPIC SYSTEM NOT WITH MICROSCOPIC SYSTEMNOT WITH MICROSCOPIC SYSTEM

ONLY CONCERNED WITH INITIAL AND ONLY CONCERNED WITH INITIAL AND FINAL STATE, NOT WITH MECHANISM OF A FINAL STATE, NOT WITH MECHANISM OF A PROCESSPROCESS

TYPES OF SYSTEMTYPES OF SYSTEM

OPEN SYSTEMOPEN SYSTEM:: IT CAN EXCHANGE BOTH MATTER AND ENERGY IT CAN EXCHANGE BOTH MATTER AND ENERGY

WITH THE SURROUNDING .WITH THE SURROUNDING .

CLOSED SYSTEMCLOSED SYSTEM::IT CAN EXCHANGE ONLY ENERGY WITH THE IT CAN EXCHANGE ONLY ENERGY WITH THE

SURROUNDING BUT NOT MATTER.SURROUNDING BUT NOT MATTER.

ISOLATED SYSTEMISOLATED SYSTEM::IT CAN NEITHER EXCHANGE MATTER NOR ENERGY.IT CAN NEITHER EXCHANGE MATTER NOR ENERGY.

HOMOGENEOUS SYSTEMHOMOGENEOUS SYSTEM::A SYSTEM IS SAID TO BE HOMOGENEOUS IF A SYSTEM IS SAID TO BE HOMOGENEOUS IF IT IS UNIFORM THROUGHOUT.IT IS UNIFORM THROUGHOUT. HETROGENEOUS SYSTEMHETROGENEOUS SYSTEM::A SYSTEM WHICH IS NOT UNIFORM THROUGH A SYSTEM WHICH IS NOT UNIFORM THROUGH OUT.OUT. MACROSCOPIC SYSTEMMACROSCOPIC SYSTEM::A SYSTEM CONTAINING LARGE AMOUNT OF A SYSTEM CONTAINING LARGE AMOUNT OF SUBSTANCE.SUBSTANCE. MACROSCOPIC PROPERTYMACROSCOPIC PROPERTY::A PROPERTY ASSOCIATED WITH THE A PROPERTY ASSOCIATED WITH THE COLLECTIVE BEHAVIOUR OF PARTICLES IN COLLECTIVE BEHAVIOUR OF PARTICLES IN MACROSCOPICMACROSCOPIC SYSTEMSYSTEM..

EXTENSIVE PROPERTIESEXTENSIVE PROPERTIES::THE PROPERTIES WHICH DEPEND UPON THE THE PROPERTIES WHICH DEPEND UPON THE QUANTITIES OF THE MATTER.QUANTITIES OF THE MATTER.EXAMPLE:MASS,VOLUME,ENERGY, HEAT EXAMPLE:MASS,VOLUME,ENERGY, HEAT CAPACITY ETC.CAPACITY ETC. INTENSIVEINTENSIVE PROPERTIESPROPERTIES: : THE PROPERTIES DEPENDING ONLY ON THE THE PROPERTIES DEPENDING ONLY ON THE AMOUNT OF THE SUBSTANCE PRESENT IN AMOUNT OF THE SUBSTANCE PRESENT IN THE SYSTEM.THE SYSTEM.EXAMPLE:TEMPERATURE, EXAMPLE:TEMPERATURE, PRESSURE,REFRACTIVE INDEX,VISCOSITY PRESSURE,REFRACTIVE INDEX,VISCOSITY ETC.ETC.

THERMODYNAMIC PROCESSTHERMODYNAMIC PROCESS1)ISOTHERMAL PROCESS1)ISOTHERMAL PROCESS::

THE PROCESS IN WHICH TEMPERATURE REMAINS THE PROCESS IN WHICH TEMPERATURE REMAINS

CONSTANT THROUGHOUT THE PROCESSCONSTANT THROUGHOUT THE PROCESS..2)ADIABETIC PROCESS2)ADIABETIC PROCESS : :

THE PROCESS IN WHICH NO HEAT CAN FLOW FROM THE PROCESS IN WHICH NO HEAT CAN FLOW FROM SYSTEM TO SURROUNDING AND SURROUNDING TO SYSTEM TO SURROUNDING AND SURROUNDING TO

SYSTEMSYSTEM..3)ISOCHORIC PROCESS3)ISOCHORIC PROCESS::

THE PROCESS DURING WHICH VOLUME OF SYSTEM THE PROCESS DURING WHICH VOLUME OF SYSTEM

IS KEPT CONSTANTIS KEPT CONSTANT..4)ISOBARIC PROCESS4)ISOBARIC PROCESS::

THE PROCESS DURING WHICH PRESSURE OF THE THE PROCESS DURING WHICH PRESSURE OF THE SYSTEM REMAINS CONSTANT.SYSTEM REMAINS CONSTANT.

REVERSIBLE PROCESSREVERSIBLE PROCESS::THE PROCESS WHICH IS CONDUCTED IN SUCH THE PROCESS WHICH IS CONDUCTED IN SUCH A MANNER THAT AT EVERY STAGE ,DRIVING A MANNER THAT AT EVERY STAGE ,DRIVING FORCE IS ONLY INFINITESIMAL GREATER THAN FORCE IS ONLY INFINITESIMAL GREATER THAN THE OPPOSING FORCE AND WHICH CAN BE THE OPPOSING FORCE AND WHICH CAN BE REVERSED BY INCREASING THE OPPOSING REVERSED BY INCREASING THE OPPOSING FORCE BY AN INFINITESIMAL AMOUNT.FORCE BY AN INFINITESIMAL AMOUNT.

IRREVERSIBLE PROCESSIRREVERSIBLE PROCESS::THE PROCESS WHICH IS NOT CARRIED OUT THE PROCESS WHICH IS NOT CARRIED OUT INFINITESIMALLY SLOWLY SO THAT THE INFINITESIMALLY SLOWLY SO THAT THE SUCCESSIVE STEPS OF THE DIRECT PROCESS SUCCESSIVE STEPS OF THE DIRECT PROCESS CAN NOT BE RETRACED AND ANY CHANGE IN CAN NOT BE RETRACED AND ANY CHANGE IN THE EXTERNAL CONDITIONS DISTURBS THE THE EXTERNAL CONDITIONS DISTURBS THE EQUILLIBRIUM.EQUILLIBRIUM.

INTERNAL ENERGYINTERNAL ENERGY::THE AMOUNT OF ENERGY ASSOCIATED WITH THE AMOUNT OF ENERGY ASSOCIATED WITH EVERY SUBSTANCE ,THE ACTUAL VALUE OF EVERY SUBSTANCE ,THE ACTUAL VALUE OF WHICH DEPENDS UPON THE NATURE OF THE WHICH DEPENDS UPON THE NATURE OF THE

SUBSTANCESUBSTANCEINTERNAL ENERGY IS A STATE INTERNAL ENERGY IS A STATE

FUNCTIONFUNCTION..WORKWORK::

WORK IS SAID TO BE DONE WHENEVER THE WORK IS SAID TO BE DONE WHENEVER THE POINT OF APPLICATION OF A FORCE IS POINT OF APPLICATION OF A FORCE IS

DISPLACED IN THE DIRECTION OF FORCE.DISPLACED IN THE DIRECTION OF FORCE.W=FORCE x DISPLACEMENT.W=FORCE x DISPLACEMENT.

WORK OF EXPANSIONWORK OF EXPANSION::

THE WORK DONE WHEN GAS THE WORK DONE WHEN GAS EXPANDS AGAINST THE EXPANDS AGAINST THE

EXTERNALPRESSUREEXTERNALPRESSURE..AREA OF CROSS SECTION =A SQ.CMAREA OF CROSS SECTION =A SQ.CM..

PRESSURE ON THE SYSTEM (SLIGHTLY LESS PRESSURE ON THE SYSTEM (SLIGHTLY LESS

THAN EXTERNALTHAN EXTERNAL PRESSURE)=PPRESSURE)=PDISPLACEMENT=dl cm.DISPLACEMENT=dl cm.

force=pressure x area=p x aforce=pressure x area=p x awork done by gas=force x distancework done by gas=force x distance

=f x dl=f x dl =p x a x dl =p x a x dl

=p x dv =p x dv

If the gas expands from vIf the gas expands from v11 to v to v

then total amount of work done,then total amount of work done, w= w= ∫p d v∫p d v

w=pw=pΔΔvv where whereΔΔv=change in volumev=change in volume

and p=external pressureand p=external pressure

SIGN CONVENTION FOR WORK SIGN CONVENTION FOR WORK DONEDONE

WORK DONE BY THE SYSTEM WORK DONE BY THE SYSTEM (W(WEXPANSIONEXPANSION)=-P)=-PΔΔVV

WORK DONE ON THE SYSTEMWORK DONE ON THE SYSTEM=+P=+PΔΔVV

STATE FUNCTION:STATE FUNCTION:A THERMODYNAMIC QUANTITY CHANGE IN A THERMODYNAMIC QUANTITY CHANGE IN THE VALUE OF WHICH DEPENDS UPON ITS THE VALUE OF WHICH DEPENDS UPON ITS VALUE IN THE INITIAL STATE AND ITS VALUE VALUE IN THE INITIAL STATE AND ITS VALUE IN THE FINAL STATE.IN THE FINAL STATE.EXAMPLE: EXAMPLE: MASS,PRESSURE, MASS,PRESSURE, VOLUME,TEMPERATURE ETCVOLUME,TEMPERATURE ETC..

PATH FUNCTION:PATH FUNCTION:A THERMODYNAMIC PROPERTY , THE A THERMODYNAMIC PROPERTY , THE CHANGE IN THE VALUE OF WHICH DEPENDS CHANGE IN THE VALUE OF WHICH DEPENDS UPON THE PATH FOLLOWED.UPON THE PATH FOLLOWED.EXAMPLE:HEAT AND WORKEXAMPLE:HEAT AND WORK..

FIRST LAW OF FIRST LAW OF THERMODYNAMICSTHERMODYNAMICS

ENERGY CAN NEITHER BE CREATED NOR ENERGY CAN NEITHER BE CREATED NOR BE DESTROYED ,MAY BE CONVERTED BE DESTROYED ,MAY BE CONVERTED FROM ONE FORM TO ANOTHR.FROM ONE FORM TO ANOTHR.

THE TOTAL ENERGY OF AN ISOLATED THE TOTAL ENERGY OF AN ISOLATED SYSTEM REMAINS CONSTANT.SYSTEM REMAINS CONSTANT.

ON DISAPPEARANCE OF CERTAIN ON DISAPPEARANCE OF CERTAIN QUANTITY OF ENERGY ,AN EQUIVALENT QUANTITY OF ENERGY ,AN EQUIVALENT AMOUNT OF SOME OTHER FORM OF AMOUNT OF SOME OTHER FORM OF ENERGY IS PRODUCED.ENERGY IS PRODUCED.

TO CONSTRUCT A PERPETUAL MACHINE IS TO CONSTRUCT A PERPETUAL MACHINE IS IMPOSSIBLE. IMPOSSIBLE.

MATHEMATICALMATHEMATICAL FORMULA FOR FIRST FORMULA FOR FIRST LAW OF THERMODYNAMICSLAW OF THERMODYNAMICS

THE INTERNAL ENERGY OF A SYSTEM THE INTERNAL ENERGY OF A SYSTEM CAN BE INCREASED IN 2 WAYS:CAN BE INCREASED IN 2 WAYS:

1)BY SUPPLYING HEAT TO THE SYSTEM1)BY SUPPLYING HEAT TO THE SYSTEM

2)BY DOING WORK ON THE SYSTEM2)BY DOING WORK ON THE SYSTEM

LET INITIAL INTERNAL ENERGY OF LET INITIAL INTERNAL ENERGY OF SYSTEM=USYSTEM=U11

IF IT ABSORBS HEAT Q, ITS INTERNAL IF IT ABSORBS HEAT Q, ITS INTERNAL ENERGY=UENERGY=U11+Q+Q

IF WORK W IS DONE ON THE IF WORK W IS DONE ON THE SYSTEM,THE INTERNAL ENERGY SYSTEM,THE INTERNAL ENERGY FURTHER INCREASED=UFURTHER INCREASED=U11+Q+W+Q+W

UU22=U=U11+Q+W+Q+W

UU22-U-U1=1=Q+WQ+W

ΔΔU=U=Q+WQ+WIF WORK DONE IS THE WORK OF IF WORK DONE IS THE WORK OF EXPANSION,W=-P EXPANSION,W=-P ΔΔVV ΔΔU=U=Q-P Q-P ΔΔVVQ= Q= ΔΔU+U+P P ΔΔVV

IF WORK W IS DONE ON THE IF WORK W IS DONE ON THE SYSTEM,THE INTERNAL ENERGY SYSTEM,THE INTERNAL ENERGY FURTHER INCREASED=UFURTHER INCREASED=U11+Q+W+Q+W

UU22=U=U11+Q+W+Q+W

UU22-U-U1=1=Q+WQ+W

ΔΔU=U=Q+WQ+WIF WORK DONE IS THE WORK OF IF WORK DONE IS THE WORK OF EXPANSION,W=-P EXPANSION,W=-P ΔΔVV ΔΔU=U=Q-P Q-P ΔΔVVQ= Q= ΔΔU+U+P P ΔΔVV

ENTHALPYENTHALPYTHE THERMODYNAMIC QUANTITY THE THERMODYNAMIC QUANTITY U+PVU+PV

IS CALLED HEAT CONTENT OR IS CALLED HEAT CONTENT OR ENTHALPY OF THE SYSTEM.ENTHALPY OF THE SYSTEM.

WHERE U=INTERNAL ENERGYWHERE U=INTERNAL ENERGY

ENTHALPY CHANGE:ENTHALPY CHANGE:ITIT IS THE SUM OF THE INCREASE IN IS THE SUM OF THE INCREASE IN

INTERNAL ENERGY OF THE SYSTEM INTERNAL ENERGY OF THE SYSTEM AND THE PRESSURE-VOLUME WORK AND THE PRESSURE-VOLUME WORK

DONEDONE..Δ Δ H=H=ΔΔU+U+P P ΔΔVV

JOULE’S LAW

THE CHANGE OF ENERGY OF AN IDEAL GAS WITH THE CHANGE OF ENERGY OF AN IDEAL GAS WITH VOLUME AT CONSTANT TEMPERATURE IS EQUAL VOLUME AT CONSTANT TEMPERATURE IS EQUAL TO ZERO.TO ZERO.AS GAS EXPANDS AGAINST VACCUM, THEREFORE AS GAS EXPANDS AGAINST VACCUM, THEREFORE

PPOPPOSINGOPPOSING=0=0

HENCE dW=HENCE dW=-P-POPPOSINGOPPOSING dV=0dV=0 USINF FIRST LAW OF THERMODYNAMICSUSINF FIRST LAW OF THERMODYNAMICS

dU=dU=δδq+ q+ δδ w w Hence Hence dU=dU=δδqq As no change in temperature takes place therefore As no change in temperature takes place therefore

δδq=0q=0 Hence Hence dU=0dU=0

U=F(V,T)U=F(V,T)dU=dU= (∂U⁄∂T) (∂U⁄∂T)VVdV+(∂U/∂V)dV+(∂U/∂V)TTdVdV

BUT dU=0 AND dT=0 BUT dU=0 AND dT=0 HENCE HENCE ((∂U ⁄ ∂ ∂U ⁄ ∂ V)V)TTdV=0dV=0AS dV≠0 IMPLIES THATAS dV≠0 IMPLIES THAT

((∂U ⁄ ∂ ∂U ⁄ ∂ V)V)TT=0=0this is joule’s lawthis is joule’s law

WHEN A REAL GAS AT A CERTAIN WHEN A REAL GAS AT A CERTAIN PRESSURE EXPANDS ADIABETICALLY PRESSURE EXPANDS ADIABETICALLY

THROUGH A POROUS PLUG OR A THROUGH A POROUS PLUG OR A FINE PLUG INTO A REGION OF LOW FINE PLUG INTO A REGION OF LOW PRESSURE , IT IS ACCOMPANIED BY PRESSURE , IT IS ACCOMPANIED BY

COOLING. THIS PHENOMENON IS COOLING. THIS PHENOMENON IS KNOWN AS KNOWN AS JOULE-THOMSON EFFECTJOULE-THOMSON EFFECT

JOULE-THOMSON EFFECTJOULE-THOMSON EFFECT

THE PROCESS IS CARRIED OUT THE PROCESS IS CARRIED OUT ADIABETICALLY ,Q=0ADIABETICALLY ,Q=0

BY FIRST LAW OF THERMODYNAMICSBY FIRST LAW OF THERMODYNAMICS,, ΔΔU=U=Q+WQ+W

ΔΔU=U=WWOR -OR -ΔΔU=-U=-WW

WORK DONE DURING THE WORK DONE DURING THE EXPANSION OF A GAS UNDER EXPANSION OF A GAS UNDER

ADIABETIC CONDITIONS IS AT THE ADIABETIC CONDITIONS IS AT THE COST OF INTERNAL ENERGY.COST OF INTERNAL ENERGY.

EXPERIMENTAL SETUPEXPERIMENTAL SETUP

On left side work is done on the On left side work is done on the system ,whereas on the right side work is system ,whereas on the right side work is

done by the system.done by the system.Work done on the system on the left Work done on the system on the left

side=pside=p11VV11

Work done by the system on the right Work done by the system on the right

side=pside=p22VV22

NetNet Work done by the system = Work done by the system =

=-p=-p22VV2+2+pp11VV11

putting this value in the equation of first law putting this value in the equation of first law of thermodynamics-of thermodynamics-

ΔΔU=U=WW ΔΔU=-U=-pp22VV2+2+pp11VV11

UU22-U-U1=1=- p- p22VV2+2+pp11VV11

UU2+2+pp22VV2=2=UU11++pp11VV11

HH2=2=HH11

THE EXPANSION OF A GAS TAKES THE EXPANSION OF A GAS TAKES

PLACE ADIABETICALLY THROUGH A PLACE ADIABETICALLY THROUGH A POROUS PLUG,THE ENTHALPY OF THE POROUS PLUG,THE ENTHALPY OF THE

SYSTEM REMAINS CONSTANTSYSTEM REMAINS CONSTANT..

THANK YOUTHANK YOU