T HERMODYNAMICS-I

1. THERMODYNAMICS-I

2. INTRODUCTION THERMODYNAMICS =THERMO+DYNAMICS THERMO MEANS HEAT AND DYNAMICS MEANS MOTION RESULTING INTO WORK THERMODYNAMICS IS THAT BRANCH OF SCIENCE WHICH DEALS WITH THE QUANTITATIVE RELATIONSHIP BETWEEN HEAT AND OTHER FORMS OF ENERGY.

3. OBJECTIVES OFTHERMODYNAMICS • TO PREDICT THE FEASIBILITY OF A PROCESS. • TO PREDICT THE YIELDS OF THE PRODUCTS. • TO DEDUCE SOME IMPORTANT GENERALISATIONS OF PHYSICAL CHEMISTRY.

4. LIMITATIONS OF THERMODYNAMICS • IT HELPS TO PREDICT FEASIBILITY OF SYSTEM ,DOES NOT TELL ABOUT THE TIME TAKEN FOR PROCESS • DEALS WITH ONLY MACROSCOPIC SYSTEM NOT WITH MICROSCOPIC SYSTEM • ONLY CONCERNED WITH INITIAL AND FINAL STATE, NOT WITH MECHANISM OF A PROCESS

5. TYPES OF SYSTEM • OPEN SYSTEM: IT CAN EXCHANGE BOTH MATTER AND ENERGY WITH THE SURROUNDING . • CLOSED SYSTEM: IT CAN EXCHANGE ONLY ENERGY WITH THE SURROUNDING BUT NOT MATTER. • ISOLATED SYSTEM: IT CAN NEITHER EXCHANGE MATTER NOR ENERGY.

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

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

9. THERMODYNAMIC PROCESS1)ISOTHERMAL PROCESS:THE PROCESS IN WHICH TEMPERATURE REMAINS CONSTANT THROUGHOUT THE PROCESS.2)ADIABETIC PROCESS :THE PROCESS IN WHICH NO HEAT CAN FLOW FROM SYSTEM TO SURROUNDING AND SURROUNDING TO SYSTEM.3)ISOCHORIC PROCESS:THE PROCESS DURING WHICH VOLUME OF SYSTEM IS KEPT CONSTANT.4)ISOBARIC PROCESS:THE PROCESS DURING WHICH PRESSURE OF THE SYSTEM REMAINS CONSTANT.

10. REVERSIBLE PROCESS:THE PROCESS WHICH IS CONDUCTED IN SUCH A MANNER THAT AT EVERY STAGE ,DRIVING FORCE IS ONLY INFINITESIMAL GREATER THAN THE OPPOSING FORCE AND WHICH CAN BE REVERSED BY INCREASING THE OPPOSING FORCE BY AN INFINITESIMAL AMOUNT.IRREVERSIBLE PROCESS:THE PROCESS WHICH IS NOT CARRIED OUT INFINITESIMALLY SLOWLY SO THAT THE SUCCESSIVE STEPS OF THE DIRECT PROCESS CAN NOT BE RETRACED AND ANY CHANGE IN THE EXTERNAL CONDITIONS DISTURBS THE EQUILLIBRIUM.

11. INTERNAL ENERGY:THE AMOUNT OF ENERGY ASSOCIATED WITH EVERY SUBSTANCE ,THE ACTUAL VALUE OF WHICH DEPENDS UPON THE NATURE OF THE SUBSTANCEINTERNAL ENERGY IS A STATE FUNCTION.WORK:WORK IS SAID TO BE DONE WHENEVER THE POINT OF APPLICATION OF A FORCE IS DISPLACED IN THE DIRECTION OF FORCE.W=FORCE x DISPLACEMENT.

12. WORK OF EXPANSION: a sq.cm. dl

13. THE WORK DONE WHEN GAS EXPANDS AGAINST THE EXTERNALPRESSURE.AREA OF CROSS SECTION =A SQ.CM.PRESSURE ON THE SYSTEM (SLIGHTLY LESS THAN EXTERNALPRESSURE)=PDISPLACEMENT=dl cm.force=pressure x area=p x awork done by gas=force x distance=f x dl =p x a x dl =p x dv

14. If the gas expands from v1 to v then total amount of work done,w= ∫p d vw=pΔv whereΔv=change in volumeand p=external pressure

15. SIGN CONVENTION FOR WORK DONE • WORK DONE BY THE SYSTEM (WEXPANSION)=-PΔV • WORK DONE ON THE SYSTEM=+PΔV WORK DONE IN THE REVERSIBLE PROCESS IS MAXIMUM

16. STATE FUNCTION:A THERMODYNAMIC QUANTITY CHANGE IN THE VALUE OF WHICH DEPENDS UPON ITS VALUE IN THE INITIAL STATE AND ITS VALUE IN THE FINAL STATE.EXAMPLE: MASS,PRESSURE, VOLUME,TEMPERATURE ETC.PATH FUNCTION:A THERMODYNAMIC PROPERTY , THE CHANGE IN THE VALUE OF WHICH DEPENDS UPON THE PATH FOLLOWED.EXAMPLE:HEAT AND WORK.

17. FIRST LAW OF THERMODYNAMICS • ENERGY CAN NEITHER BE CREATED NOR BE DESTROYED ,MAY BE CONVERTED FROM ONE FORM TO ANOTHR. • THE TOTAL ENERGY OF AN ISOLATED SYSTEM REMAINS CONSTANT. • ON DISAPPEARANCE OF CERTAIN QUANTITY OF ENERGY ,AN EQUIVALENT AMOUNT OF SOME OTHER FORM OF ENERGY IS PRODUCED. • TO CONSTRUCT A PERPETUAL MACHINE IS IMPOSSIBLE.

19. MATHEMATICAL FORMULA FOR FIRST LAW OF THERMODYNAMICS THE INTERNAL ENERGY OF A SYSTEM CAN BE INCREASED IN 2 WAYS: 1)BY SUPPLYING HEAT TO THE SYSTEM 2)BY DOING WORK ON THE SYSTEM LET INITIAL INTERNAL ENERGY OF SYSTEM=U1 IF IT ABSORBS HEAT Q, ITS INTERNAL ENERGY=U1+Q

20. IF WORK W IS DONE ON THE SYSTEM,THE INTERNAL ENERGY FURTHER INCREASED=U1+Q+WU2=U1+Q+WU2-U1=Q+WΔU=Q+WIF WORK DONE IS THE WORK OF EXPANSION,W=-P ΔVΔU=Q-P ΔVQ= ΔU+P ΔV

21. ENTHALPY THE THERMODYNAMIC QUANTITY U+PV IS CALLED HEAT CONTENT OR ENTHALPY OF THE SYSTEM. WHERE U=INTERNAL ENERGY ENTHALPY CHANGE: IT IS THE SUM OF THE INCREASE IN INTERNAL ENERGY OF THE SYSTEM AND THE PRESSURE-VOLUME WORK DONE. Δ H=ΔU+P ΔV

22. JOULE’S LAW

23. THE CHANGE OF ENERGY OF AN IDEAL GAS WITH VOLUME AT CONSTANT TEMPERATURE IS EQUAL TO ZERO.AS GAS EXPANDS AGAINST VACCUM, THEREFORE POPPOSING=0 HENCE dW=-POPPOSINGdV=0 USINF FIRST LAW OF THERMODYNAMICS dU=δq+ δ w Hence dU=δq As no change in temperature takes place therefore δq=0 Hence dU=0

24. U=F(V,T)dU= (∂U⁄∂T)VdV+(∂U/∂V)TdVBUT dU=0 AND dT=0 HENCE (∂U ⁄ ∂ V)TdV=0AS dV≠0 IMPLIES THAT(∂U ⁄ ∂ V)T=0this is joule’s law

25. WHEN A REAL GAS AT A CERTAIN PRESSURE EXPANDS ADIABETICALLY THROUGH A POROUS PLUG OR A FINE PLUG INTO A REGION OF LOW PRESSURE , IT IS ACCOMPANIED BY COOLING. THIS PHENOMENON IS KNOWN AS JOULE-THOMSON EFFECT JOULE-THOMSON EFFECT

26. THE PROCESS IS CARRIED OUT ADIABETICALLY ,Q=0BY FIRST LAW OF THERMODYNAMICS,ΔU=Q+WΔU=WOR -ΔU=-WWORK DONE DURING THE EXPANSION OF A GAS UNDER ADIABETIC CONDITIONS IS AT THE COST OF INTERNAL ENERGY.

27. EXPERIMENTAL SETUP

28. On left side work is done on the system ,whereas on the right side work is done by the system.Work done on the system on the left side=p1V1Work done by the system on the right side=p2V2NetWork done by the system = =-p2V2+p1V1putting this value in the equation of first law of thermodynamics-

29. ΔU=WΔU=-p2V2+p1V1U2-U1=- p2V2+p1V1U2+p2V2=U1+p1V1H2=H1THE EXPANSION OF A GAS TAKES PLACE ADIABETICALLY THROUGH A POROUS PLUG,THE ENTHALPY OF THE SYSTEM REMAINS CONSTANT.

30. THANK YOU