What does it mean? The total energy in the universe stays the same. If a system gains energy, that energy must have come from somewhere else. If it loses energy, that energy goes somewhere else.

What does it mean?
The total energy in the universe stays the same.
If a system gains energy, that energy must have come from somewhere else.
If it loses energy, that energy goes somewhere else.

1. First Law of Thermodynamics

2. What is the First Law of Thermodynamics?
Thestudyofrelationsbetweenwork,heatandtemperatureand
theirrelationswithenergy,entropy,andphysicalpropertiesof
matter.Thermodynamicsexplainhowmatterisaffectedbythe
processwhenthermalenergyisconvertedtoorfromtheother
formsofenergy,andtheprocessitself.
Theenergythatisreleasedfromheatisknownasthermalenergy.
Thisgeneratedheatallowsthemovementofparticleswithinan
objectandasthespeedoftheseparticlesincrease,moreheatis
generated.

3. There are four laws of thermodynamics
which are as follows-
Zeroth Law of Thermodynamics
First Law of Thermodynamics
Second Law of Thermodynamics
Third Law of Thermodynamics

5. First Law of Thermodynamics
Thefirstlawofthermodynamicsstatesthatthequantityoftheheatabsorbed,
whensomeamountofheatisgiventoasystemthatiscapableofdoingexternal
work,isequaltothesumoftheincreaseininternalenergyofthesystemdueto
ariseintemperatureandexternalworkdoneduringexpansion.
The first law of thermodynamics is generally represented by the equation-
ΔU = Q − W
Where:
ΔU = Change in internal energy of the thermodynamic system–Joule (J)
Q = Heat given to the system –Joule (J)
W = Work done on the system –Joule (J)

6. Thefirstlawofthermodynamicsistheapplicationof
theconservationofenergyprincipletoheatand
thermodynamicprocesses:

7. Thefirstlawmakesuseofthekeyconceptsofinternal
energy,heat,andsystemwork.
Itisusedextensivelyinthediscussionofheatengines.
Thestandardunitforallthesequantitieswouldbethe
Joule,althoughtheyaresometimesexpressedincalories
orBTUs.(Britishthermalunit)

8. Itistypicalforchemistrytextstowritethe
firstlawasΔU=Q-W.
ItisjustthatWisdefinedasthework
doneonthesysteminsteadofwork
donebythesystem.

9. Term Definition
U=Internalenergy—thesumofthekineticandpotentialenergiesofa
system’satomsandmolecules.Canbedividedintomanysubcategories,suchas
thermalandchemicalenergy.Dependsonlyonthestateofasystem(suchasits
P,V,andT),notonhowtheenergyenteredthesystem.Changeininternal
energyispathindependent.
Q=Heat—energytransferredbecauseofatemperaturedifference.
Characterizedbyrandommolecularmotion.Highlydependentonpath.Q
enteringasystemispositive.
W=Work—energytransferredbyaforcemovingthroughadistance.An
organized,orderlyprocess.Pathdependent.Wdonebyasystem(eitheragainst
anexternalforceortoincreasethevolumeofthesystem)ispositive.

10. ThefirstlawofThermodynamicsisalso
called‘LawofConservationofEnergy’.
Thelawofconservationofenergy
statesthat“Energycanneitherbe
destroyednorbecreated,itcanonlybe
transferredfromoneformtoanother”.

11. Significance of First Law of Thermodynamics
Therelationbetweenheatandworkisestablishedbythe
firstlawofthermodynamics.
BothWorkandHeatareequivalenttoeachother.
Theexactequivalentamountofenergyofthe
surroundingwillbelostorgained,ifanysystemgainsor
losesenergy.
Appliedheatisalwaysequaltothesumofworkdoneand
changeininternalenergy.
Theenergyisconstantforanisolatedsystem.

12. Applications of First Law of Thermodynamics
Thefirstlawofthermodynamicsiscommonlyusedinheat
engines.
Refrigeratorsisanotherexamplewherethefirstlawof
thermodynamicsisused.
Sweatingisagreatexampleofthefirstlawof
thermodynamicssincetheheatofthebodyistransferredto
sweat.
Whenanicecubeisputinadrink,theicecubesabsorb
theheatofthedrinkwhichmakesitcool.

13. Limitations of First Law of Thermodynamics
Thefirstlawofthermodynamicsdoesnot
stateanythingabouttheheatflowdirection.
Theprocessisnotreversible.
Itisdifficulttodistinguishwhetherthe
processisspontaneousornot.

14. 4 Processes that are involved in a closed
system
1.AdiabaticProcess-Atypeofthermodynamic
processwherethereisnotransferofheator
massbetweenthesurroundingsandthesystem.
Example-Rapidcontractionandexpansionofa
gas.

15. 4 Processes that are involved in a closed
system
AdiabaticProcessExample-Rapidcontractionandexpansionofagas.

16. 4 Processes that are involved in a closed
system
2.Isothermalprocess-Atypeofthermodynamicprocessin
whichthereisnochangeinthetemperaturethatisitremains
constant.Example-Refrigerator
Arefrigeratorworksisothermally.Asetofchangestakeplacein
themechanismofarefrigeratorbutthetemperatureinside
remainsconstant.
Inthermodynamics,anisothermalprocessisatypeof
thermodynamicprocessinwhichthetemperatureTofasystem
remainsconstant:ΔT=0

18. 4 Processes that are involved in a closed
system
3.IsobaricProcess-Atypeofthermodynamicprocess
inwhichthereisnochangeintheprocessthatisit
remainsconstantpressure.
Example-waterboilingandconvertingtosteam

20. 4 Processes that are involved in a closed
system
4.IsochoricProcess-Atypeofthermodynamicprocessin
whichthereisnochangeinthevolumewhichmeansthe
volumeisconstant.
Example-Pressurecookers
Ifyouclosetheboilingpan,likeinapressurecooker,volume
staysthesameandpressurestartstogrow.Socookingina
pressurecookerisanisochoricprocess.

22. Summary of Thermodynamic Process
Isothermal ProcessConstant temperature
Adiabatic Process No heat involved
Isobaric Process Constant pressure
Isochoric Process Constantvolume

23. Sign Convention used for heat and work
in thermodynamics
ThesignconventionsforEnergyandWorkareas
follows-
If energy enters into the system, it is +
If energy leaves out of the system, it is -
If work done is ‘by’ the system, it is +
If work done is ‘on’ the system, it is -

24. Sign Convention used for Heat and Work
in Thermodynamics
The sign conventions for Heat and Work are as
follows-
When Q is +, heat flows into the system
When Q is -, heat flows out of the system
When W is +, energy leaves the system
When W is -, energy enters the system

25. What is the meaning of entropy in
Thermodynamics?
Themeasureofenergythatisnotavailabletodo
workisknownasentropy.Inthecaseofareversible
process,thechangeinentropyiszerowhileinthe
caseofanirreversibleprocessthereisanincreasein
entropy.
Entropycanonlybeincreasedorremainzero,itcan
neverbedecreased.Unlikeenergy,entropyisnever
conserved,italwaysincreases.

26. Specific heat of a gas
Theinternalenergyofanidealgasdependsonlyonits
temperatureandnottoitsvolumeorpressure.Thespecific
heatofagasataconstantpressureisgreaterthanitsspecific
heatatconstantvolume.Thespecificheatofagasisdefinedby
theequation:
Cp= Cv+ R
Where:
Cv= constant volume
Cp= constant pressure
R = Universal gas constant 8.3145 J/mol°K

27. Ratio of specific heat of a gas
Itistheratioofthespecificheatofagasata
constantvolume.Theratioofheatcapacitiesisdefined
bytheequation.
Y = Cp/ Cv
Where:
Y= Ratio of molar heat capacities(lamba) = no unit

28. Cv= constant volume
Cp= constant pressure

29. Summary
ThefirstlawofthermodynamicsisgivenasΔU=Q−W,whereΔUisthe
changeininternalenergyofasystem,Qisthenetheattransfer(thesumofall
heattransferintoandoutofthesystem),andWisthenetworkdone(the
sumofallworkdoneonorbythesystem).
BothQandWareenergyintransit;onlyΔUrepresentsanindependent
quantitycapableofbeingstored.
TheinternalenergyUofasystemdependsonlyonthestateofthesystem
andnothowitreachedthatstate.
Metabolismoflivingorganisms,andphotosynthesisofplants,arespecialized
typesofheattransfer,doingwork,andinternalenergyofsystems.

30. 750 calories of heat is added to a system and the system
performs 550 calories of work. Calculate the change in Internal
Energy.
Given:
Q = 750 cal
W = 550 cal
ΔU = Q -W
= (+750) –(+550)
= +200 calories is the increase in internal energy
The sign conventions :
Qis positive if the heat added to the system
Wis positive if work is done by the system
Qis negative if heat leaves the system
Wis negative if work is done on the system

31. Question:
A system absorbs 881 J of heat while performing 1,424 J of work on its
surroundings. Calculatethe internal energy (ΔU)in Joules.
Energy is conserved
Energycancrosstheedgesorperimeterofaclosedsystemasheat
(movementofthermalenergy)orwork(movementofaforce).The
internalenergyofthesystemchangesasitinteractswithheatandwork
sothatenergyisneithermissingnorexcess.

32. Answer and Explanation:
Here's the information that we need to use:
ΔUis the internal energy change.
Qis the heat transfer
Wis the work done
The heat entering the system is positive. The work done by the system
on the environment is positive.

33. Let's determine the internal energy change of the system by means of the first law
of thermodynamics.
Problem: A system absorbs 881 J of heat while performing 1,424 Jof work on its
surroundings. Calculateinternal energy ΔUin Joules (J).
ΔU = Q−W
= (+881J) − (+1424J)
ΔU = −543J
The negative sign indicates that the internal energy of the system decreases.
The sign conventions :
Qis positive if the heat added to the system
Wis positive if work is done by the system
Qis negative if heat leaves the system
Wis negative if work is done on the system

34. Problem Solving
3000 J ofheatis added to a system and 2500 J ofworkis done by the
system. What is the change in internal energy of the system?
Known :
Heat(Q) = +3000 Joule
Work(W) = +2500 Joule
Wanted:the change in internal energy of the system
Solution :
The equation ofthe first law of thermodynamics
ΔU = Q-W

35. Heat(Q) = +3000 Joule
Work(W) = +2500 Joule
ΔU = ?
The change in internal energy of the system :
ΔU = Q-W
ΔU = (+3000) –(+2500)
ΔU = +500 Joule
Internal energy increases by 500 Joule.
The sign conventions :
Qis positive if the heat added to the system
Wis positive if work is done by the system
Qis negative if heat leaves the system
Wis negative if work is done on the system

36. End