Material Science & Thermodynamics Presentation.pdf

7/27/2019 Material Science & Thermodynamics Presentation.pdf

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EMA 4521CEMA 4521C

Materials Science IMaterials Science I

Lecture 1Lecture 1

Arvind AgarwalArvind Agarwal

Department of Mechanical and Materials EngineeringDepartment of Mechanical and Materials Engineering

Florida International UniversityFlorida International University


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UniverseUniverse

System SurroundingsSystem Surroundings

ClosedClosed OpenOpen No matter enter or leavesNo matter enter or leaves Matter is allow to flowMatter is allow to flow

but energy can go in or outbut energy can go in or out in or outin or out

Boundaries may expand/contractBoundaries may expand/contract

due to work done by or on the systemdue to work done by or on the system


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Combination of closedCombination of closedand open systemand open system

Car engineCar engine


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Heat and workHeat and work

Energy transformedEnergy transformed

Heat (Q)Heat (Q) Work (W)Work (W)Transform occur Transform canTransform occur Transform can

due todue toTT occur by all othersoccur by all others

forms of energyforms of energy

(elect, magnetic,(elect, magnetic,mechmech))


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ConventionConvention

When heat goes into theWhen heat goes into thesystem from surroundingsystem from surrounding

Q > 0Q > 0 QQ

Heat (Q) is energy in transitHeat (Q) is energy in transit

due to temp. differencedue to temp. difference((T)T)..

Q is aQ is aflowflowquantity andquantity andnot stored by the system.not stored by the system.

System storesSystem storesthermal/heat energythermal/heat energyandandnot heat.not heat.

Heat Energy is referred asHeat Energy is referred asEnthalpy (H)Enthalpy (H)


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Enthalpy (H)Enthalpy (H)

Heat (Q) is transfer across the boundary ofHeat (Q) is transfer across the boundary ofa system due to temperature differentiala system due to temperature differential

((T) between system and surroundings.T) between system and surroundings.

NoteNote: System: System does notdoes not contain heat (Q) butcontain heat (Q) butHeat Energy (H) . Heat is energy in transit.Heat Energy (H) . Heat is energy in transit.

Heat Energy is also referred as Enthalpy (H)Heat Energy is also referred as Enthalpy (H)


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Internal EnergyInternal Energy

Total Energy can be divided as = KineticTotal Energy can be divided as = KineticEnergy + Potential Energy + InternalEnergy + Potential Energy + InternalEnergyEnergy

Thus, Total Energy= Internal Energy (U)Thus, Total Energy= Internal Energy (U) Internal Energy (U) is due toInternal Energy (U) is due toinherentinherent

qualities (motion of atoms and molecules inqualities (motion of atoms and molecules inthe matter) as well asthe matter) as well asenvironmentalenvironmental

variables (temp, pressure, elec. field,variables (temp, pressure, elec. field, magmag U= f (material properties, composition,U= f (material properties, composition,

pressure ,temperature)pressure ,temperature)

0

0


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Basic Postulate ofBasic Postulate ofThermodynamicsThermodynamics

Entire concept is build on theEntire concept is build on theequilibriumequilibriumstatesstates

Postulate: Change in ThermodynamicPostulate: Change in Thermodynamic

PropertyProperty does notdoes notdepend on path thedepend on path thesystem took to get between two states.system took to get between two states.

It means that thermodynamic property isIt means that thermodynamic property is

dependent on INITIAL and FINAL stage onlydependent on INITIAL and FINAL stage only


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State FunctionsState Functions

Thermodynamics properties DO NOT dependThermodynamics properties DO NOT dependon path, but depended on states.on path, but depended on states.

S,S,G,G,U all are state functions.U all are state functions.

Work done NOT a state functionWork done NOT a state function

Internal Energy State functionInternal Energy State function


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WorkWork

In contrast to U, WorkIn contrast to U, Workis not a state functionis not a state function

Work is pathWork is pathdependentdependent

(Path function(Path functionrepresented byrepresented by i.e.i.e.W)W)

Similarly, Q (heat) isSimilarly, Q (heat) is

also path dependentalso path dependentand written asand written as QQ

But loosely speakingBut loosely speakingwe keep on writingwe keep on writing QQ

== dQdQ andand W=W=dWdW


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First Law :First Law :Energy can not be created or destroyed.Energy can not be created or destroyed.

To derive practical benefits of this law, we are creating an accTo derive practical benefits of this law, we are creating an accountingounting

systemsystem needs defining various thermodynamic properties and rules.needs defining various thermodynamic properties and rules.

Total energy of systemTotal energy of systemplus surroundings is constantplus surroundings is constant

Conservation of EnergyConservation of Energy


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dQdQ

dWdW

dUdU== dQdQ dWdW dWdW ExpansionExpansion

Work doneWork done BYBY

the system =the system = PdVPdV Expansion:Expansion:

dVdV= V2= V2--V1V1

V2> V1V2> V1 dVdV> 0> 0 PdVPdV> 0> 0

dUdU== dQdQ PdVPdV

SameSame

So no difference just follow one??So no difference just follow one??

dQdQ dWdW

dUdU== dQdQ ++ dWdW dWdW ContractionContraction

Work doneWork done ONON thethesystem =system = PdVPdV

Contraction:Contraction:

dVdV= V2= V2--V1V1

V2< V1V2< V1 dVdV


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Enthalpy (H)Enthalpy (H)

Heat (Q) is transfer across the boundary ofHeat (Q) is transfer across the boundary ofa system due to temperature differentiala system due to temperature differential

((T) between system and surroundings.T) between system and surroundings.

NoteNote: System: System does notdoes not contain heat (Q)butcontain heat (Q)butHeat Energy (H) . Heat is energy in transit.Heat Energy (H) . Heat is energy in transit.

Heat Energy is also referred as Enthalpy (H)Heat Energy is also referred as Enthalpy (H)


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EnthalpyEnthalpy

Q=Q= dUdU ++ PdVPdV (from First Law)(from First Law)= d(U+PV) at constant pressure= d(U+PV) at constant pressure

Thus,Thus, Q=Q= dHdH at constant pressureat constant pressure H= U + PV is defined as enthalpyH= U + PV is defined as enthalpy

H0 Endothermic

QQ WW


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EnthalpyEnthalpy


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Intensive and ExtensiveIntensive and ExtensivePropertiesProperties

1.1. Extensive properties (Extensive properties (mass, volume,mass, volume,internal energyinternal energy) depend upon sample) depend upon sample

size.size.

2.2. Intensive properties (Intensive properties (temperature,temperature,

pressure, density, specific volumepressure, density, specific volume))

do not depend upon the sample size.do not depend upon the sample size.


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Specific PropertiesSpecific Properties

Properties per unit mass (kg or mole) areProperties per unit mass (kg or mole) arespecific properties.specific properties.

E.g. U, V, G, Cp,E.g. U, V, G, Cp, CvCv

Per Mole properties are calledPer Mole properties are calledMolarMolarpropertiespropertiesQuestion 1: Are specific propertiesQuestion 1: Are specific propertiesintensiveintensiveoror

extensive?extensive?

Question 2: what is the specific volume of water?Question 2: what is the specific volume of water?Density = 1g/cc at 298 KDensity = 1g/cc at 298 K

Answer: 10 expAnswer: 10 exp3 m3/kg3 m3/kg


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Heat CapacityHeat Capacity

Energy regard to increase temperature of aEnergy regard to increase temperature of abody by 1K.body by 1K.

Specific Heat CapacitySpecific Heat Capacity::

Energy to raise the temperature of 1 gm ofEnergy to raise the temperature of 1 gm ofsubstance by 1 K.substance by 1 K.

Molar Heat CapacityMolar Heat Capacity::

Energy to raise the temperature of 1 mol ofEnergy to raise the temperature of 1 mol ofsubstance by 1 K.substance by 1 K.


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Heat CapacityHeat Capacity

There are two definitions for vaporsThere are two definitions for vaporsand gases:and gases:

CpCp = Specific heat capacity at= Specific heat capacity at

constant pressure, i.e.constant pressure, i.e.

CvCv = Specific heat capacity at= Specific heat capacity at

constant volume, i.e.constant volume, i.e.


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Most of the metallurgical proceduresMost of the metallurgical proceduresare at constant pressure rather thanare at constant pressure rather than

constant volumeconstant volume

At constant pressureAt constant pressure Q =Q = dHdH

T2T2 T2T2

dHdH == CpCp dTdT KirchoffKirchoffEqEq..T1T1 T1T1


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T2T2

H2H2 H1 =H1 = CpCp dTdTT1T1

T2T2

HH22(T)= H(T)= H1100 ++ CpCp dTdT

T1T1

EnthalpyEnthalpy at absolute zero cant be defined. But we doat absolute zero cant be defined. But we doneed a reference point. So, we choseneed a reference point. So, we chose

HH1100 : Reference State (298 K, 1: Reference State (298 K, 1 atmatm) occurs when) occurs whenelements exist in equilibrium conditionelements exist in equilibrium condition

E.g. Diatomic O2, pure Ag, pure Al, pure CuE.g. Diatomic O2, pure Ag, pure Al, pure Cu

HformationHformation < 0 ;< 0 ;HformationHformation > 0> 0


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For a reaction:For a reaction:

A + B C + DA + B C + D

T2T2

HH22(T)= H(T)= H1100 ++ [[CpCp productproduct++CpCp reactreact ]] dtdt

T1T1

By HessBy Hesss Laws Law

Enthalpy of formation when 1 mol ofEnthalpy of formation when 1 mol ofcompound ( product) is formedcompound ( product) is formed


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HessHesss Laws Law

If a reaction isIf a reaction iscarried out in acarried out in a

several steps,several steps,H ofH of

the reaction will bethe reaction will beequal to sum of theequal to sum of the

enthalpy changesenthalpy changes

for the individualfor the individual

step.step.


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Latent HeatLatent Heat

Heat needed to change the state ofHeat needed to change the state ofmattermatter

S L VS L V

LLfusionfusion: quantity of heat energy released: quantity of heat energy releasedwhen 1 unit weight of a substancewhen 1 unit weight of a substance

solidifies without change thesolidifies without change thetemperaturetemperature


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EMA 4521 CEMA 4521 C

Materials Science IMaterials Science I

Arvind AgarwalArvind Agarwal

Department of Mechanical and Materials EngineeringDepartment of Mechanical and Materials Engineering

Florida International UniversityFlorida International University


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First LawFirst Law

dUdU == dQdQ ++ dWdWdUdU == dQdQ PdVPdV dQdQ

dQdQ == dUdU ++ PdVPdV

dQdQ

= d(U + PV) If P is constant= d(U + PV) If P is constant

dQdQ == dHdH H= U + PVH= U + PV dWdW

Heat Energy = Enthalpy at constant pressureHeat Energy = Enthalpy at constant pressure

H< 0 Exothermic (E.g.H< 0 Exothermic (E.g. ThermiteThermite reaction)reaction)H> 0 EndothermicH> 0 Endothermic


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We defined heat capacityWe defined heat capacity

Cp = (Cp = (Q/Q/T)p = (T)p = (H/H/T)T) CvCv = (= (Q/Q/T)v = (T)v = (U/U/T)T)

T2 T2T2 T2

dHdH == CpdTCpdTT1 T1T1 T1

Cp = f(t)Cp = f(t)


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HessHesss Laws Law

HessHesss Law: If a reaction is carried out in a series ofs Law: If a reaction is carried out in a series ofsteps,steps,H for the total reaction will be equal to theH for the total reaction will be equal to thesum ofsum ofHHii for each step.for each step.


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NewNew

Heat of ReactionHeat of Reaction

Heat of reaction: is the heat involved or absorbedHeat of reaction: is the heat involved or absorbedwhen reactants react completely to form products.when reactants react completely to form products.

(Unit:(Unit: -- per mole of any reactant or product)per mole of any reactant or product)

A + B C + DA + B C + D

Heat of =Heat of = Heat productHeat product -- Heat of reactantsHeat of reactants

reactionreaction


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Example 1Example 1

CHCH44 + 2O+ 2O22 COCO22 + 2H+ 2H22O (g)O (g)

HH00reaction = 2reaction = 2HH00HH22O +O +HH00COCO22

-- 22HH00OO22 --HH00CHCH44

00

HH00

HH22O =O = --241.8 KJ241.8 KJHH00COCO22 == --393.5 KJ393.5 KJ

HH00CHCH44 == --74.8 KJ74.8 KJ

HH00reaction =reaction = --802 KJ at 298 K802 KJ at 298 K


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Heat of FormationHeat of Formation

The heat of formation of a compoundThe heat of formation of a compound(per mole) is the heat evolved or(per mole) is the heat evolved or

absorbed (i.e. change in enthalpy)absorbed (i.e. change in enthalpy)

when 1 mole of compound forms fromwhen 1 mole of compound forms fromits constituents elements or substancesits constituents elements or substances

e.g. Ni(s) +e.g. Ni(s) + O2(g) =O2(g) = NiONiO (s)(s)


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Heat of formation = f(temp, pressure,Heat of formation = f(temp, pressure,chemical state of reactants and products)chemical state of reactants and products)

Hence, we define heat of formation atHence, we define heat of formation at

standard state I.e. 298 K and 1standard state I.e. 298 K and 1AtmAtm.. Heat of formation of a compound from itsHeat of formation of a compound from its

standard statestandard stateis called Standard Heat ofis called Standard Heat of

Formation. It is denoted byFormation. It is denoted byHH00

298.298.i.e.i.e.HH00298, M298, M for a metal Mfor a metal M

Heat of FormationHeat of Formation


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ConventionConvention

< M > solid< M > solid { M } liquid{ M } liquid

( M ) gas( M ) gas

Or Ms, MOr Ms, ML,L, MMG.G.


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Concept of ReferenceConcept of ReferenceStateState

H = HH = H22 HH11 U, or H can never be defined inU, or H can never be defined in

absolute terms. There is no absoluteabsolute terms. There is no absolute

zero of energy.zero of energy.

There has to be some reference.There has to be some reference.

We define reference or standard stateWe define reference or standard state(25 degrees C or 298K and 1(25 degrees C or 298K and 1 atmatm))


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Major AssumptionMajor Assumption

Enthalpy (Enthalpy (HH00298298 )of O2 at reference)of O2 at reference

state = 0state = 0

Enthalpy (Enthalpy (HH00298298 )of pure substances)of pure substances

at reference state = 0at reference state = 0


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If pure elements/substances areIf pure elements/substances are

assumed to have zero enthalpy atassumed to have zero enthalpy atreference state their compound mustreference state their compound must

have some other values.have some other values.

ExampleExample

C + OC + O22 COCO22 (at 298 K)(at 298 K)

H react =H react = nnppproductsproducts nnrrreactionreaction==HcoHco22 --HcHc --HoHo22

0 00 0== --393.5 KJ/mol reference393.5 KJ/mol reference

statestate


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To findTo find

H at temperature other thanH at temperature other than

298 K298 K

((HH00

//T) =T) =CCppT1T1

HH00TT22 --HH

00TT11 == CpdTCpdT

T2T2

T1T1

HH00

TT22 ==HH00TT11 ++ CpCpprodprodCpCpreactreactT2T2


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Example 3Example 3

Page 10, Example 1.C,Page 10, Example 1.C, DubeDube UpadhyayaUpadhyaya BookBook

About + (O2) =


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Entropy and the SecondEntropy and the Second

Law of ThermodynamicsLaw of Thermodynamics

Second Law of thermodynamics defines a termSecond Law of thermodynamics defines a termentropyentropywhich tells aboutwhich tells aboutspontaneityspontaneityof theof thereaction or thereaction or thedirectiondirectionof the reaction.of the reaction.

The world is inherently active.The world is inherently active.

Whenever an energy distribution is out of equilibriumWhenever an energy distribution is out of equilibrium(e.g. temp. difference) a potential or thermodynamic(e.g. temp. difference) a potential or thermodynamic

"force"forceexists that the world acts spontaneously toexists that the world acts spontaneously todissipate or minimize.dissipate or minimize. (This minimization results in(This minimization results inmaximization of entropy)maximization of entropy)


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Reversible ProcessReversible Process

Reversible Process: is that whichReversible Process: is that whichhaven taken place could be reversedhaven taken place could be reversedand in doing so leaves no change isand in doing so leaves no change is

systemsystemororsurroundingsurrounding. (. (This mayThis may

happen if there is no friction, no unrestrained expansion andhappen if there is no friction, no unrestrained expansion andheat transfer only due to infinitesimal temperature difference)heat transfer only due to infinitesimal temperature difference)

For a reversible processFor a reversible processSSsystemsystem ++SSsurroundingsurrounding = 0= 0


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Irreversible ProcessIrreversible Process

Most of theMost of thenaturalnaturalprocesses areprocesses areirreversibleirreversible..

For an irreversible (I.e. spontaneousFor an irreversible (I.e. spontaneous

process)process)SSsystemsystem ++SSsurroundingsurrounding > 0> 0

Entropy is not conserved in naturalEntropy is not conserved in naturalprocesses.processes.


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Entropy and the SecondEntropy and the Second

Law of ThermodynamicsLaw of Thermodynamics

The balance equation of the secondThe balance equation of the secondlaw, expressed as S > 0, says that inlaw, expressed as S > 0, says that in

allall naturalnaturalprocesses the entropy ofprocesses the entropy of

the world always increases.the world always increases.

Entropy is a measure of disorder.Entropy is a measure of disorder.


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Entropy: MathematicalEntropy: Mathematical

ConceptConcept

Entropy like energy is NOT conserved (Entropy like energy is NOT conserved (To prove:To prove:

Give as HW problemGive as HW problem))

dSdS== QrevQrev/T =/T = dHdH/T =/T = nCpdTnCpdT/ T/ T

Q =Q = dHdH (at const. Pressure)(at const. Pressure)

SS22 TT22 dsds == CpCp dTdT/T/T

SS11 TT11


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EntropyEntropy

State Function (Proof beyond thisState Function (Proof beyond thiscourse)course)

Extensive Property (i.e. depends onExtensive Property (i.e. depends on

mass or # of moles).mass or # of moles). Units: Cal/deg/mole orUnits: Cal/deg/mole or

Joules/deg/moleJoules/deg/mole


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Change in Enthalpy andChange in Enthalpy and

Entropy During MeltingEntropy During Melting


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Gibbs Free EnergyGibbs Free Energy

TheThe Gibbs Free EnergyGibbs Free Energyis a thermodynamicis a thermodynamicquantity which can be used to determine ifquantity which can be used to determine ifa reaction isa reaction is spontaneousspontaneous or not.or not.

The definition of the Gibbs free energy isThe definition of the Gibbs free energy is dGdG== dHdH TdSTdS. The sign of. The sign ofdGdG determines if adetermines if areaction is spontaneous or not.reaction is spontaneous or not.

dGdG < 0: the reaction is spontaneous< 0: the reaction is spontaneous

dGdG > 0: the reaction is not spontaneous> 0: the reaction is not spontaneous

dGdG = 0: the reaction is at= 0: the reaction is at equilibriumequilibrium

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Material Science & Thermodynamics Presentation.pdf