THERMODYNAMICS-I

1
THERMODYNAMICS-I
2
INTRODUCTION

• THERMODYNAMICS THERMODYNAMICS
• 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 OF THERMODYNAMICS

• 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.

6
(No Transcript)
7
HOMOGENEOUS SYSTEMA SYSTEM IS
SAID TO BE HOMOGENEOUS IF IT IS UNIFORM
THROUGHOUT. HETROGENEOUS SYSTEMA
SYSTEM WHICH IS NOT UNIFORM THROUGH OUT.
MACROSCOPIC SYSTEMA SYSTEM CONTAINING
LARGE AMOUNT OF SUBSTANCE.
MACROSCOPIC PROPERTYA PROPERTY ASSOCIATED WITH
THE COLLECTIVE BEHAVIOUR OF PARTICLES IN
MACROSCOPIC SYSTEM.
8
EXTENSIVE PROPERTIESTHE PROPERTIES WHICH DEPEND
UPON THE QUANTITIES OF THE MATTER.EXAMPLEMASS,VO
LUME,ENERGY, HEAT CAPACITY ETC. INTENSIVE
PROPERTIES THE PROPERTIES DEPENDING ONLY ON THE
AMOUNT OF THE SUBSTANCE PRESENT IN THE
SYSTEM.EXAMPLETEMPERATURE, PRESSURE,REFRACTIVE
INDEX,VISCOSITY ETC.
9
THERMODYNAMIC PROCESS1)ISOTHERMAL PROCESSTHE
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
PROCESSTHE PROCESS DURING WHICH VOLUME OF
SYSTEM IS KEPT CONSTANT.4)ISOBARIC PROCESSTHE
PROCESS DURING WHICH PRESSURE OF THE SYSTEM
REMAINS CONSTANT.
10
REVERSIBLE PROCESSTHE 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 PROCESSTHE 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 ENERGYTHE AMOUNT OF ENERGY ASSOCIATED
WITH EVERY SUBSTANCE ,THE ACTUAL VALUE OF WHICH
DEPENDS UPON THE NATURE OF THE SUBSTANCEINTERNAL
ENERGY IS A STATE FUNCTION.WORKWORK IS SAID TO
BE DONE WHENEVER THE POINT OF APPLICATION OF A
FORCE IS DISPLACED IN THE DIRECTION OF
FORCE.WFORCE 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
EXTERNAL PRESSURE)PDISPLACEMENTdl
cm.forcepressure x areap x awork done by
gasforce 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 vwp?v
where?vchange in volumeand pexternal pressure
15
SIGN CONVENTION FOR WORK DONE

• WORK DONE BY THE SYSTEM (WEXPANSION)-P?V
• WORK DONE ON THE SYSTEMP?V

WORK DONE IN THE REVERSIBLE PROCESS IS MAXIMUM
16
STATE FUNCTIONA 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 FUNCTIONA THERMODYNAMIC PROPERTY ,
THE CHANGE IN THE VALUE OF WHICH DEPENDS UPON THE
PATH FOLLOWED.EXAMPLEHEAT 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.

18
(No Transcript)
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 SYSTEMU1
• IF IT ABSORBS HEAT Q, ITS INTERNAL ENERGYU1Q

20
IF WORK W IS DONE ON THE SYSTEM,THE INTERNAL
ENERGY FURTHER INCREASEDU1QWU2U1QWU2-U1Q
W ?UQWIF WORK DONE IS THE WORK OF
EXPANSION,W-P ?V ?UQ-P ?VQ ?UP ?V
21
ENTHALPY

• THE THERMODYNAMIC QUANTITY UPV IS CALLED HEAT
  CONTENT OR ENTHALPY OF THE SYSTEM.
• WHERE UINTERNAL ENERGY
• ENTHALPY CHANGE
• IT IS THE SUM OF THE INCREASE IN INTERNAL ENERGY
  OF THE SYSTEM AND THE PRESSURE-VOLUME WORK DONE.
• ? H?UP ?V

22
JOULES 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
• POPPOSING0
• HENCE dW-POPPOSING dV0
• USINF FIRST LAW OF THERMODYNAMICS
• dUdq d w
• Hence dUdq
• As no change in temperature takes place therefore
  dq0
• Hence dU0

24
UF(V,T)dU (?U/?T)VdV(?U/?V)TdVBUT dU0 AND
dT0 HENCE (?U / ? V)TdV0AS dV?0 IMPLIES
THAT(?U / ? V)T0this is joules 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 ,Q0BY
FIRST LAW OF THERMODYNAMICS, ?UQW ?UWOR
-?U-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
sidep1V1 Work done by the system on the right
sidep2V2Net Work done by the system
-p2V2p1V1putting this value in the equation
of first law of thermodynamics-
29
?UW ?U-p2V2p1V1U2-U1- p2V2p1V1U2p2V2U1p
1V1H2H1 THE EXPANSION OF A GAS TAKES PLACE
ADIABETICALLY THROUGH A POROUS PLUG,THE ENTHALPY
OF THE SYSTEM REMAINS CONSTANT.
30
THANK YOU