chapter 17: energy and kinetics
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Pages 510-547. Chapter 17: Energy and Kinetics. Thermochemistry : Causes of change in systems Kinetics : Rate of reaction progress (speed). Heat , Energy , and Temperature changes. Standard unit of heat is the Joule , J Standard unit of temperature is Kelvin , K. - PowerPoint PPT PresentationTRANSCRIPT
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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Bires, 2010-b Slide 3
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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Bires, 2010-b Slide 4
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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Bires, 2010-b Slide 5
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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Bires, 2010-b Slide 6
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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Bires, 2010-b Slide 7
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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Bires, 2010-b Slide 8
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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Bires, 2010-b Slide 9
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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Bires, 2010-b Slide 10
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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Bires, 2010-b Slide 12
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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Bires, 2010-b Slide 13
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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Bires, 2010-b Slide 14
Exothermic Reaction: products have lower energy than do the reactants. What if endothermic?
Hrxn
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Bires, 2010-b Slide 15
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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Bires, 2010-b Slide 16
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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Bires, 2010-b Slide 17
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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Bires, 2010-b Slide 18
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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Bires, 2010-b Slide 19
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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Bires, 2010-b Slide 20
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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Bires, 2010-b Slide 21
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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Bires, 2010-b Slide 22
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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Bires, 2010-b Slide 23
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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Bires, 2010-b Slide 24
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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Bires, 2010-b Slide 25
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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Bires, 2010-b Slide 26
G = G = H - TH - TSS
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Bires, 2010-b Slide 27
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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Bires, 2010-b Slide 28
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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Bires, 2010-b Slide 29
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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Bires, 2010-b Slide 30
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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Bires, 2010-b Slide 31
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)