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BackBackChapter 17: Energy and Chapter 17: Energy and KineticsKinetics

ThermochemistryThermochemistry::Causes of change in systemsCauses of change in systems

KineticsKinetics::Rate of reaction progress (speed)Rate of reaction progress (speed)

HeatHeat,, EnergyEnergy, and, and Temperature Temperature changeschanges

Standard unit of heat is the Joule, J

Standard unit of temperature is Kelvin, K

Pages 510-547

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Bires, 2010-b Slide 2

HeatHeat vs vs TemperatureTemperature

HeatHeat– measure of measure of energy changeenergy change in a system. in a system.

TemperatureTemperature– measure of the measure of the averageaverage kinetic energy kinetic energy

(movement) of the particles in a system.(movement) of the particles in a system. ExothermicExothermic

– System System loses energyloses energy to surroundings to surroundings EndothermicEndothermic

– System System gains energygains energy from surroundings from surroundings

K = C + 273.15

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Specific HeatSpecific Heat Specific HeatSpecific Heat

– measure of measure of how a substance reacts to heat how a substance reacts to heat energyenergy changes. changes.

– Think Think thermal inertiathermal inertia– is the is the heat energy required to raise heat energy required to raise one gram one gram

of a pure substance one degreeof a pure substance one degree Celsius Celsius..– is a property of matter; different species have is a property of matter; different species have

different different Specific HeatsSpecific Heats..

The symbol we use is The symbol we use is ccpp..– The “p” stands for The “p” stands for constant pressureconstant pressure while heat is added or while heat is added or

lostlost..

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Specific Heat Specific Heat CapacityCapacity

Metals have very low Metals have very low ccpp,,– which is why metals often which is why metals often

feel cold to the touch.feel cold to the touch. Water has a Water has a very highvery high

ccpp, , – 44..184184 J/g· J/g·00CC

Substances with Substances with lower lower ccpp will will rise in temperature fasterrise in temperature faster and require less energy to and require less energy to do so than do substances do so than do substances with high with high ccpp..

SubstanceSubstanceJ/(g x J/(g x ooC)C)

or J/(g x K)or J/(g x K)cal/(g x cal/(g x ooC) C)

or cal/(g x K)or cal/(g x K)

Water (0 Water (0 ooC to 100 C to 100 ooC)C) 4.1844.184 1.0001.000

ZincZinc .387.387 0.0930.093

Ice (-10 Ice (-10 ooC to 0 C to 0 ooC)C) 2.0932.093 0.5000.500

Steam (100 Steam (100 ooC)C) 2.0092.009 0.4800.480

BrassBrass .380.380 0.0920.092

Wood (typical)Wood (typical) 1.6741.674 0.4000.400

Soil (typical)Soil (typical) 1.0461.046 0.2500.250

Air (50 Air (50 ooC)C) 1.0461.046 0.2500.250

AluminumAluminum .900.900 0.2150.215

TinTin .227.227 0.2050.205

Glass (typical)Glass (typical) .837.837 0.2000.200

Iron/SteelIron/Steel .452.452 0.1080.108

CopperCopper .387.387 0.09240.0924

SilverSilver .236.236 0.05640.0564

MercuryMercury .138.138 0.03300.0330

GoldGold .130.130 0.03100.0310

LeadLead .128.128 0.03050.0305

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Specific Heat CapacitySpecific Heat Capacity

CCpp units are units are J/gJ/g00CC)) Change inChange in heatheat ((joulesjoules, , JJ))

== Change inChange in temperaturetemperature (degree, (degree, 00CC))

xx MassMass (mass, g) (mass, g)

xx Specific Heat CapacitySpecific Heat Capacity (4.184 for water)(4.184 for water)

pcmTQ

1 calorie = 4.184 Joules

Cp (H2O) = 4.184

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Specific Heat Specific Heat Example Example ExerciseExercise

Determine the specific heat of Determine the specific heat of 34 grams34 grams of an unknown material if of an unknown material if 485 J485 J of heat of heat are absorbed to change the temperature are absorbed to change the temperature by by 20.0 20.0 ooCC..

If If 950 J950 J of heat are added to of heat are added to 5.4 mL5.4 mL of of water at water at 280 K280 K, what will be the resulting , what will be the resulting temperature of the water? temperature of the water? (hint: mL (hint: mL g) g)

pcmTQ

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The Calorimeter The Calorimeter (shown)

Heat energy is transferred from a reaction inside the calorimeter to the water in the calorimeter.

The temperature change of the water is observed.

Text page 519

When two objects are in contact, they eventually obtain Thermal Equilibrium; their temperatures become equal.

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EEnntthhaallppyy,, ΔΔHH EnthalpyEnthalpy

– heat energyheat energy transferredtransferred for a for a specific changespecific change to take place.to take place.

We specify We specify enthalpyenthalpy with with ΔΔHH. “. “ΔΔ” means ” means “change in”.“change in”.

ExothermicExothermic reaction reaction – negative enthalpynegative enthalpy ( (--ΔΔH H ))

EndothermicEndothermic reaction reaction– Positive enthalpyPositive enthalpy ( (++ΔΔHH))..

Elements in their standard (elemental) state Elements in their standard (elemental) state have a have a ΔΔH of zero.H of zero.– OO2,2, Fe, Cu, N Fe, Cu, N22, He, etc are have H, He, etc are have Hff = 0 kj/mol = 0 kj/mol

The universe favors LOW energy states - if the products have lower energy reaction is favored.

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EEnntthhaallppyy,, ΔΔHH Some common changes involving Some common changes involving ΔΔHH:: ΔΔHHfusfus == heat of heat of fusionfusion ΔΔHHvapvap == heat of heat of vaporizationvaporization ΔΔHHcondcond == heat of heat of condensationcondensation ΔΔHHsubsub == heat of heat of sublimationsublimation ΔΔHHrxnrxn == heat of heat of reactionreaction ΔΔHHff == heat of heat of formationformation ΔΔHHsolsol == heat of heat of solutionsolution ΔΔHHcombcomb == heat of heat of combustioncombustion

State change to/from?

Sign of ΔH?

Changes of State.mov

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Phase ChangesPhase Changes1.1. Solid + heat = temp Solid + heat = temp ▲▲

2.2. Solid + heat = phase changeSolid + heat = phase change

3.3. Liquid + heat = ?Liquid + heat = ?

4.4. And then…?And then…?

5.5. Gas + heat = ?Gas + heat = ?

tem

pera

ture

Heat added

mLQ

TcmQ tem

pera

ture

Heat added

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Reaction Reaction EEnntthhaallppyy If If ΔΔHH is negative, the reaction is is negative, the reaction is exothermicexothermic..

CC66HH1212OO66 + 6O + 6O22 6CO6CO22 + 6H + 6H22O + O + 2870kJ2870kJ

ΔΔHHrxnrxn = = -2870 kJ/mol-2870 kJ/mol

If If ΔΔHH is positive, the reaction is is positive, the reaction is endothermicendothermic..

2H2H22O + O + 571.6kJ571.6kJ 2H 2H22 + O + O22

ΔΔHHrxnrxn = = +571.6 kJ/mol+571.6 kJ/mol

energy

energy

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SpontaneitySpontaneity SpontaneousSpontaneous– A reaction that will proceed on its own once A reaction that will proceed on its own once

started.started. Sometimes, all the reaction needs to get going Sometimes, all the reaction needs to get going

is the is the kinetic energykinetic energy of nearby of nearby collidingcolliding atoms. atoms. Kinetic Molecular Theory:Kinetic Molecular Theory:

– All Matter is made of particles in constant motionAll Matter is made of particles in constant motion– Some collisions are more energetic than others. Some collisions are more energetic than others.

Why?Why?

Spontaneous combustionSpontaneous combustion– occurs when the occurs when the kinetic energy of colliding oxygen kinetic energy of colliding oxygen

moleculesmolecules striking a fuel have enough energy on striking a fuel have enough energy on their own to start the combustion reaction.their own to start the combustion reaction.

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Exothermic Reaction: products have lower energy than do the reactants. What if endothermic?

Hrxn

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In the diagram, the hump is called a activation energy barrier - the amount of energy required for the reaction to begin.

All reactions require some sort of activation energy , Ea.

We can reduce the activation energy with a catalyst.

Activated complex

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Hess’s Law:Hess’s Law:– If two reactions begin with the If two reactions begin with the same same

reactants in the same conditionreactants in the same condition and end with and end with the the same products in the same conditionsame products in the same condition, , they must have the they must have the same enthalpy changesame enthalpy change..

– It doesn’t matter if you perform a reaction in several It doesn’t matter if you perform a reaction in several steps or produce your final product in one step, the steps or produce your final product in one step, the enthalpy change will be the same.enthalpy change will be the same.

Consider the reaction Consider the reaction A +A + B B DD : :

AA + + BB + + 100 kJ100 kJ CC thenthen CC + + 50 kJ 50 kJ DD

Must be the same as Must be the same as AA + + BB + + 150 kJ150 kJ DD

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Hess’s LawHess’s LawEnthalpy of ReactionEnthalpy of Reaction

ΔΔHHrxnrxn = ∑H = ∑Hproductsproducts – – ∑H∑Hreactantsreactants

==

ΣΣHHff,, all the products all the products – – ΣΣHHff,, all the reactantsall the reactants

“ Sum of ”

Enthalpy of Formation

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Hess’s Law Example ExerciseHess’s Law Example Exercise

ΔΔHHrxnrxn = ∑H = ∑Hproductsproducts – ∑H – ∑Hreactantsreactants

Calculate the Calculate the heat of reactionheat of reaction when when 350 grams350 grams of of methane, methane, CHCH44 are burned in excess oxygen. are burned in excess oxygen. HHff book values for each species are:book values for each species are:

CHCH4(g)4(g) = -74.8 kJ/mol= -74.8 kJ/mol

OO2(g)2(g) = ?= ?

HH22OO(g)(g) = -285.83 kJ/mol= -285.83 kJ/mol

COCO2(g)2(g) = -393.5 kJ/mol= -393.5 kJ/mol

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EEnnttrrooppyy, , ΔΔSS EntropyEntropy– is a measure of is a measure of relative disorderrelative disorder. .

Thermodynamics tells us that the Thermodynamics tells us that the universe tends towards disorder or universe tends towards disorder or entropyentropy..

– Temperature affects entropyTemperature affects entropy (why?) (why?) Entropy calculations are very similar Entropy calculations are very similar

to enthalpy calculations:to enthalpy calculations:

ΔΔSSrxnrxn = = ΣΣSSproductsproducts – – ΣΣSSreactantsreactantsEntropy has the unit J/K*mol

EntropyandTemperature.swf

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EEnnttrrooppy, y, ΔΔSS The universe tends towards entropyThe universe tends towards entropy

– entropy plays a part in predicting whether or entropy plays a part in predicting whether or not a reaction will be not a reaction will be spontaneousspontaneous..

SolidsSolids have have very low entropyvery low entropy GasesGases have have very high entropyvery high entropy SolutionsSolutions also have also have high entropyhigh entropy

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QualitativeQualitative E Ennttrrooppyy Values Values We can make generalizations about a We can make generalizations about a

reaction’s entropy;reaction’s entropy;

22KClOKClO33(s)(s) 22KClKCl(s)(s) + + 33OO22(g)(g)

2 solids 2 solids 2 solids + 3 gases 2 solids + 3 gases

Entropy appears to Entropy appears to increaseincrease in this in this reaction.reaction.

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Quantitative EQuantitative Ennttrrooppyy Values Values22KClOKClO3(s)3(s) 22KClKCl(s)(s) + + 33OO2(g)2(g)

S S of of KClOKClO3(s)3(s) == 143.7 143.7 J/mol*KJ/mol*K

S S of of KClKCl(s)(s) == 82.6 82.6 J/mol*KJ/mol*K

S S ofof O O2(g)2(g) == 205.1 205.1 J/mol*KJ/mol*K

Using Using ΔΔSSrxnrxn = = SSproductsproducts – – SSreactantsreactants, the , the reaction has a total reaction has a total eennttrrooppyy change change of of ++493.1 493.1 J/mol*KJ/mol*K

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EEnnttrrooppyy Values Values A A positivepositive ΔΔS S = = increase in entropyincrease in entropy A A negativenegative ΔΔS S = = decrease in entropydecrease in entropy

Do not confuse entropy and enthalpy!Do not confuse entropy and enthalpy!

Tending toward Tending toward spontaneityspontaneity::

Negative Negative EEnntthhaallppyy ((--ΔΔHH))Positive Positive EEnnttrrooppyy (+(+ΔΔS)S)

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Free EnergyFree Energy, , ΔΔGG Free energyFree energy, , ΔΔGG::– allows us to assign a value to an entire allows us to assign a value to an entire

reaction to predict reaction to predict whether a reaction is whether a reaction is spontaneousspontaneous, , product favoredproduct favored..

– or or nonspontaneousnonspontaneous, , reactant-favoredreactant-favored..– Named for American Chemist, J. Willard GibbsNamed for American Chemist, J. Willard Gibbs

ΔΔG = G = ΔΔH -TH -TΔΔSSFree

Energy kJ/mol

EnthalpykJ/mol

temperature in Kelvin

Entropy J/mol·K

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Gibbs Free Energy, Gibbs Free Energy, ΔΔGGrxnrxn

Negative Gibbs Energy (-Negative Gibbs Energy (-ΔΔGGrxnrxn))

SpontaneousSpontaneous, , Product favoredProduct favored

Positive Gibbs Energy (+Positive Gibbs Energy (+ΔΔGGrxnrxn))

NonspontaneousNonspontaneous, , Reactant favoredReactant favored

A ΔG of zero means that neither the products nor reactants are favored-the

reaction is in equilibrium.

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G = G = H - TH - TSS

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Reaction RatesReaction Rates Reaction ratesReaction rates

– how fast a reaction proceedshow fast a reaction proceeds.. Some factors will affect reaction rate:Some factors will affect reaction rate:

TemperatureTemperature of reactants: of reactants: higherhigher = = fasterfaster ConcentrationConcentration of reactants: of reactants: greatergreater = = fasterfaster Surface areaSurface area of reactants: of reactants: greatergreater = = fasterfaster

– (powders react faster than chunks)(powders react faster than chunks) PressurePressure of gaseous reactants: of gaseous reactants: greatergreater = = fasterfaster Catalyst presenceCatalyst presence: : catalystscatalysts make rxns make rxns fasterfaster

– reduce activation energy!reduce activation energy!– are not used up (not reactants)are not used up (not reactants)

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Rate LawsRate Laws For any reaction:For any reaction:

The The raterate is based on the [reactants]: is based on the [reactants]:

[X][X] : “1 : “1stst order” : order” : 2x2x [A][A] , , 2x2x rate rate [X][X]2 2 :: “2 “2ndnd order” : order” : 2x2x [A][A] , , 4x4x rate rate [X][X]3 3 :: “3 “3rdrd order” : order” : 2x2x [A][A] , , 8x8x rate rate

dDcCbBaA

]][[ BAkRate ][AkRate2][AkRate3][AkRate

End of C17, conclusion follows

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In conclusion…In conclusion…

Specific Heat CapacitySpecific Heat Capacity, , ccpp ((J/gKJ/gK))– the amount of heat energy required to raise 1 the amount of heat energy required to raise 1

gram, 1 degreegram, 1 degree EnthalpyEnthalpy, , ΔΔH H ((kJkJ/mol/mol))

– the heat energy transferred in a reactionthe heat energy transferred in a reaction EntropyEntropy, , ΔΔSS ((JJ/mol-K/mol-K))

– the change in disorder of the species in a the change in disorder of the species in a reactionreaction

Gibbs Free EnergyGibbs Free Energy, , ΔΔGG ((kJkJ/mol/mol))– measure of spontaneity; how product favored measure of spontaneity; how product favored

or reactant favored a reaction isor reactant favored a reaction is

Recall that K = C + 273.15

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CCSD Syllabus ObjectivesCCSD Syllabus Objectives 16.1: Thermodynamics, definition16.1: Thermodynamics, definition 16.2: Exothermic/Endothermic16.2: Exothermic/Endothermic 16.3: Changes in Enthalpy16.3: Changes in Enthalpy 16.4: Thermochemical Calculations16.4: Thermochemical Calculations 16.5: Energy Diagrams16.5: Energy Diagrams 16.6: Enthalpy-Entropy-Free Energy16.6: Enthalpy-Entropy-Free Energy 17.1: Kinetics Definition17.1: Kinetics Definition 17.2: Factors that Affect Reaction Rate17.2: Factors that Affect Reaction Rate

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Aligned Labs and DemosAligned Labs and Demos Lab: Flaming Cheeto Calorimetry LabLab: Flaming Cheeto Calorimetry Lab Lab: Metals Calorimetry LabLab: Metals Calorimetry Lab Lab: NaOH-HCl Enthalpy of Reaction LabLab: NaOH-HCl Enthalpy of Reaction Lab Lab: Ba(OH)Lab: Ba(OH)22-8H-8H22O w/ NHO w/ NH44NONO33 and H and H22OO22

with a catalyst Free Energy Labwith a catalyst Free Energy Lab Lab: KI-HLab: KI-H22OO22 Kinetics Lab Kinetics Lab Demo: Carbon Snake with powdered vs Demo: Carbon Snake with powdered vs

granular sugar (Kinetics)granular sugar (Kinetics)

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