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Do-Now: “Ch. 10 Quiz Day Do-Now” 1. Write down today’s FLT 2. What is the equation for heat? 3. Write the equation above in terms of specific heat. 4. What is the equation for ΔH°
rxn? 5. What are the steps for solving for ΔH°
rxn? 6. Take out your calculator, periodic table, planner, and ToC. 7. Turn in your lab.
FLT • I will be able to identify and describe the
factors that determine the spontaneity of a reaction by completing Entropy & Free Energy Notes
Standard HS-PS3-1:Createacomputationalmodeltocalculatethechangeintheenergyofonecomponentinasystemwhenthechangeinenergyoftheothercomponent(s)andenergyflowsinandoutofthesystemareknown
Recall • Thermodynamics: • The study of energy changes that
accompany chemical and physical processes
The First Law of Thermodynamics • Law of conservation of energy
– The 1st Law of Thermodynamics: – Application of the law of conservation of
energy to heat and thermodynamic processes.
– Energy cannot be created or destroyed, but it can be changed.
The First Law of Thermodynamics • Law of conservation of energy
– ΔH = Change in enthalpy – ΔH0
f = Standard Molar Enthalpy of Formation
Reversible Reactions • Reactions can occur in the forward and
reverse directions. • Ex/ ClNO2 + NO ßà NO2 + ClNO
Spontaneous Processes • Types of Processes:
– Spontaneous = naturally occurs under a given set of conditions.
Spontaneous Processes • Types of Processes:
– Nonspontaneous = does not occur under a given set of conditions.
Spontaneous Processes • If a process is spontaneous in the forward
direction, then the reverse process will be nonspontaneous.
Spontaneous Processes • What makes a process spontaneous?
– Systems like to be at a lower state of energy • Most (not all) spontaneous processes are also exothermic (ΔH < 0) and release energy
Spontaneous Processes • What makes a process spontaneous?
– Systems like to be become more disordered/random • High entropy
Entropy • Entropy (S) = a measure of the disorder or
randomness of a system. – Entropy increases as the number of possible
microstates increases
Entropy • Physical States
– Solids are highly ordered à lowest entropy
– Gas molecules move rapidly and randomly à highest entropy
Entropy • Trends for Standard Entropy values
– Solids < liquids < gases – More complex molecules have higher
entropies (greater vibrational energy)
Pair-Share-Respond 1. Distinguishbetweenspontaneousandnonspontaneousprocesses
2. Systemsliketobeata______energy(enthalpy)stateand______disordered/random(entropy)state
3. Whatdeterminesspontaneity?4. Define“entropy”5. Whichwouldhaveahigherentropy:iceorvapor?
The Second Law of Thermodynamics • Second Law of Thermodynamics =
– The entropy of the universe always increases for a spontaneous process
The Second Law of Thermodynamics • ΔS is usually positive (ΔS > 0) when
1. Solid à Liquid à Gas 2. The total number of gas molecules
increases 3. A larger molecule is broken into 2 or more
smaller molecules
The Second Law of Thermodynamics • Predict whether ΔS is + or –
– 2SO2(g) + O2(g) ßà 2SO3 (g) • ΔS is…
– CaCO3(s) ßà CaO(s) + CO2(g) • ΔS is…
– AgBr(s)ßà Ag+(aq) + Br-
(aq) • ΔS is …
Gibbs Free Energy • ΔG = Gibbs Free Energy
– “Available” energy à Energy that we can actually use to do work
Gibbs Free Energy • ΔG = Gibbs Free Energy
– This is contrast to enthalpy (H), which represents the total energy of the system
Gibbs Free Energy • ΔG = Gibbs Free Energy
– The energy that is actually available has to factor in the entropy of the system
Gibbs Free Energy • ΔG = ΔH – TΔS • ΔG = Δ Gibbs free energy • ΔH = Δ Enthalpy • T = Temperature in K • ΔS = Δ Entropy
ΔG = ΔH – TΔS • Relationship between ΔG and Spontaneity:
– ΔG < 0 , – Spontaneous process in the forward
direction; releases energy
ΔG = ΔH – TΔS • Relationship between ΔG and Spontaneity:
– ΔG > 0 , – Nonspontaneous process in the forward
direction
ΔG = ΔH – TΔS • Relationship between ΔG and Spontaneity:
– ΔG = 0 , – System is at equilibrium; no net change
occurs
ΔG = ΔH – TΔS
ΔH ΔS ΔG ReactionOutcome
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ΔH ΔS ΔG ReactionOutcome
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ΔH ΔS ΔG ReactionOutcome
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ΔH ΔS ΔG ReactionOutcome
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ΔH ΔS ΔG ReactionOutcome
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Pair-Share-Respond 1. Whatdoesthe2ndlawofthermodynamicstellus?
2. WhatarethreewaysthatΔSwillbecomepositive?
3. DefineGibbsFreeEnergy4. WhatistheequationforGibbsFreeEnergy?
5. UnderwhatΔHandΔSconditionswillΔGalwaysbepositive?
Do-Now: “Video Notes: Kinetics” 1. Write down today’s FLT 2. How does ΔH differ between exothermic and
endothermic reactions? 3. What two factors determine “spontaneity”? 4. What does it mean if ΔG < 0? 5. What does “molarity” refer to? 6. Bob is performing a chemical reaction in a
lab, but his reaction is going very slowly. What do you think Bob could do to speed up the reaction? Make an educated guess if necessary.
7. Take out your ToC and planner J
Video Notes • Before we start our new notes, we will
watch a video overviewing the concept of chemical kinetics
• During the video, write down five facts that you learn about kinetics
• Focus on new information
FLT • I will be able to identify four factors that
influence the rate of a chemical reaction by completing Kinetics Notes Part A
Standard HS-PS1-5:Applyscientificprinciplesandevidencetoprovideanexplanationabouttheeffectsofchangingthetemperatureorconcentrationofthereactingparticlesontherateatwhichareactionoccurs
Recall • Thermodynamics: • The study of energy changes that
accompany chemical and physical processes
Recall • If we are discussing thermodynamically
favorability, what should we be considering? • Do any of these factors give us information
about the rate of a reaction?
Collision Theory • When suitable particles of the reactant hit each
other, only a certain % of the collisions cause any noticeable or significant chemical change
Collision Theory • Collision Theory (to successfully create
products): ① Molecules must collide with sufficient
activation energy ② Molecules must collide in the correct
orientation • Only successful collisions will lead to chemical
changes (breaking preexisting bonds and forming all new bonds)
• This results in the products of the reaction
Energy Diagrams • Activation Energy (Ea) = the minimum E
required for molecules to react • Ea is the difference in energy from the reactants
to the peak of the energy diagram
Energy Diagrams • The peak represents a high energy transition
state (called the activated complex ). Bonds are breaking/forming before the final products are made.
Factors That Affect Rxn Rate 1. Temperature 2. Surface Area 3. Concentration 4. Presence of a Catalyst
Factors That Affect Rxn Rate 1. Temperature • Higher T = Higher rxn rate • Increasing the T increases the avg. KE of molecules. • Faster molecules = more collisions = more
successful collisions • Higher E collisions = more successful collisions
Factors That Affect Rxn Rate • This means it’s more likely that bonds will be
broken and new bonds will form. • An increase in T produces more successful
collisions that are able to overcome the needed activation energy, therefore, a general increase in rxn rate with increasing T
Factors That Affect Rxn Rate 2. Surface Area • Greater SA = Greater rxn rate • The amount of “exposed surface” will directly
affect speed
Factors That Affect Rxn Rate 3. Concentration • Higher Conc’ of reactants = Higher rxn rate
(usually) • The more molecules present, the more collisions
occur, the faster the reaction proceeds, the greater the rate.
Factors That Affect Rxn Rate 4. Presence of a Catalyst • Catalysts = substances that speed up rxns • Catalysts are not consumed in chemical rxns,
and can be reused
Factors That Affect Rxn Rate • Most catalysts work by lowering the Ea
needed for the rxn to proceed – therefore, collisions are more successful and the rate increases
• We can see this in a rxn pathway
Pair-Share-Respond 1. Definetheterm“reactionrate”2. Whatarefourfactorsthataffectrxn
rate?3. Explainhowtemperatureaffectsthe
reactionrate.Bespecific.4. Notallreactantsformproducts.What
doescollisiontheorytellusaboutwhichreactantsareabletoformproducts?
5. Defineactivationenergyandhowcatalystscanaffectit.
Do-Now: “Video Notes: Rate Laws” 1. Write down today’s FLT 2. Identify four factors that can affect the rate of
a chemical reaction 3. What are the units of concentration? 4. What are the standard units of time? 5. Solve: (0.20 M)2 ÷ 0.10 s = ? 6. Create an energy diagram for an
endothermic reaction. Label the axes, reactants, products, Ea, and ΔH.
7. Add a dashed line to your diagram in #6 that demonstrates the effect of adding a catalyst. Label any relevant terms.
8. Take out your ToC and planner J
Video Notes • Wewillwatchaportionofthevideoonratelaws
• Duringthistime,writedownatleastFOURnewfacts,whichmustincludeinformationaboutwritingratelaws
FLT • I will be able to write the rate laws for
chemical reactiosn by completing Kinetics Notes Part B
Standard HS-PS1-5:Applyscientificprinciplesandevidencetoprovideanexplanationabouttheeffectsofchangingthetemperatureorconcentrationofthereactingparticlesontherateatwhichareactionoccurs
Factors That Affect Rxn Rate 1. Temperature 2. Surface Area 3. Concentration 4. Presence of a Catalyst
ReactionRate• Asareactionproceedsovertime,theconcentrationofthereactantdecreases,andtheconcentrationofaproductincreases.
RateLaws• Ratestypicallydecreaseasreactantconcentrationsdecrease– Fewerreactantmolecules=fewerinteractions/collisions
• Thismakesitdifficulttomeasurerates,astheyareconstantlychanging,oftenfasterthanwecanmeasure
RateLaws• Ratelaw=Themathematicalrelationshipbetweentherateofachemicalreactionandtheconcentrationofreactants
• Inaratelaw,weonlylookatthereactants
TheRateLawForAàproducts
Rate=k[A]n• k=rateconstant(constantofproportionality)• n=reactionorder
• Remember:bracketsrepresenttheconcentrationinMolarity,so[A]means“themolarconcentrationofA”
TheRateLawForAàproducts
Rate=k[A]n• Whatistherateconstant?• Itisanumericalvaluethatisspecifictoagiventemperature
• Theunitsofkvary–youmustsolveforkbypluggingintoseewhatunitsareleft!
TheRateLawForAàproducts
Rate=k[A]n• Whatisthereactionorder?• Itistheexponentthatdefineshowtherateisaffectedbytheconcentrationofthatreactant
• Typically,we’llseethattheexponentiseither0,1,or2
• Think–whathappenstoourequationiftheexponentis0?
ForAàproductsRate=k[A]n
• Mostcommonrxnorders:– n=0àZeroorderrxnàrateisindependentof[A](doubling[A]hasnoeffectonrate)
– n=1à1storderrxnàrateisdirectlyproportionalto[A](doubling[A]doublestherate)
– n=2à2ndorderrxnàrateisproportionalto[A]2(doubling[A]quadruplestherate)
RateLaws• Whatshouldyouknowrightnow?• Ratesaretypically0order,1storder,or2ndorder• Theorderbecomestheexponentinourratelaw
RateLaws• Whatdotheordersmean?• Simplyhowtheconcentrationofareactantaffectstherateoftheoverallreaction
RateLaws• Whatifwehavemultiplereactantsandproducts?• Givenareactionintheformof:
aA+bBàcC+dD• Theratelawexpressionwouldbe:
Rate=k[A]m[B]n• Wherekistherateconstant,[]=molarity,andmandnarethereactionorders.
• Theoverallorderoftherxn=m+n
Theratelawshouldbedeterminedexperimentally.
Ex1/• Whatwouldtheratelawexpressionbefor:
C3H6O+Br2àC3H5OBr+HBr• Theratelawwouldhavetheform:
Rate=k[C3H6O]m[Br2]n
• Notethatthisisanexpressionoftheratelaw.• Theorderofthereactionwithrespectto[C3H6O]ism
• Theorderofthereactionwithrespectto[Br2]isn• Theoverallorderofthereactionism+n
RateLaws• Theorderofareactioncanbedeterminedonlybyexperiment
• Fromdata,wecanusethemethodofinitialratestodeterminereactionorder
• Forthismethod,areactionisrunseveraltimeswithdifferentinitialreactantconcentrationstodeterminetheeffectofconcentrationontherate.
Ex/2• GivenAàproducts,writetheratelawexpressionforthereaction.Then,solveforkandplug-in.
• [A](M) InitialRate(M/s)0.10 0.0150.20 0.0300.40 0.060
TryThis:• DeterminetheratelawforthedatabelowforthereactionAàproducts,andthensolve:
[A](M) InitialRate(M/s)0.10 0.015
0.20 0.015
0.40 0.015
Solution:• Rate=k[A]0• Rate=k• Rate=0.015M/s
[A](M) InitialRate(M/s)0.10 0.015
0.20 0.015
0.40 0.015
TryThis:• Determinetheratelawexpressionforthedatabelow:
[A](M) InitialRate(M/s)0.10 0.015
0.20 0.060
0.40 0.240
Solution:• Rate=k[A]2• 0.015M/s=k[0.10M]2• k=(0.015M/s)/(0.010M2)• k=1.5s-1M-1• Rate=(1.5s-1M-1)[A]2
[A](M) InitialRate(M/s)0.10 0.015
0.20 0.060
0.40 0.240
Ex/3• Considerthereactionbetweennitrogendioxideandcarbonmonoxide:NO2(g)+CO(g)àNO(g)+CO2(g)
• Fromthedata,determine:a. Theratelawforthereactionb. Therateconstant(k)forthereaction
[NO2](M) [CO](M) InitialRate(M/s)
0.10 0.10 0.0021
0.20 0.10 0.0082
0.20 0.20 0.0083
0.40 0.10 0.033
Ex/• Rate=k[NO2]m[CO]n• IfIdouble[NO2]butkeep[CO]constant,whathappenstotherate?
• Som=2• (remember–youcanalsofindthismathematically)
[NO2](M) [CO](M) InitialRate(M/s)
0.10 0.10 0.0021
0.20 0.10 0.0082
0.20 0.20 0.0083
0.40 0.10 0.033
Ex/• Rate=k[NO2]2[CO]n• IfIdouble[CO]butkeep[NO2]constant,whathappenstotherate?
• Son=0
[NO2](M) [CO](M) InitialRate(M/s)
0.10 0.10 0.0021
0.20 0.10 0.0082
0.20 0.20 0.0083
0.40 0.10 0.033
Ex/• Rate=k[NO2]2[CO]0• Rate=k[NO2]2• Nowfindkthroughsubstitution• k=0.21M-1s-1
[NO2](M) [CO](M) InitialRate(M/s)
0.10 0.10 0.0021
0.20 0.10 0.0082
0.20 0.20 0.0083
0.40 0.10 0.033