chemistry day 75 - weebly

Chemistry Day 75 Friday, April 19th – Monday, April 22nd, 2019

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

Entropy and Free Energy

Recall

Recall •  Thermodynamics: •  The study of energy changes that

accompany chemical and physical processes

The First Law of Thermodynamics

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

Reversible Reactions •  Reactions can occur in the forward and

reverse directions. •  Ex/ ClNO2 + NO ßà NO2 + ClNO

Spontaneous Processes

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

Spontaneous Processes •  Spontaneity is determined by ΔH (enthalpy)

and ΔS (entropy)

Entropy

Entropy •  Entropy (S) = a measure of the disorder or

randomness of a system. – Entropy increases as the number of possible

microstates increases

Entropy •  ΔS = change in entropy •  ΔS > 0 means the system increased in

disorder.

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 2nd Law of Thermodynamics

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

Gibbs Free Energy •  ΔG = Gibbs Free Energy

– “Available” energy à Energy that we can actually use to do work


– This is contrast to enthalpy (H), which represents the total energy of the system


– 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 > 0 , – Nonspontaneous process in the forward

direction


– ΔG = 0 , – System is at equilibrium; no net change

occurs

ΔG = ΔH – TΔS

ΔH ΔS ΔG ReactionOutcome

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Always- Rxnisspontaneousat_________________________________

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Always- Rxnisspontaneousatalltemperatures

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Rxnis__________________________________

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Always+ Rxnisnonspontaneousatalltemperatures

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-atlowT+athighT

Rxnisspontaneousatlowtemperatures

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-atlowT+athighT

Rxnisspontaneousatlowtemperatures

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+atlowT-athighT

Rxnisspontaneousathightemperatures

Pair-Share-Respond 1.  Whatdoesthe2ndlawofthermodynamicstellus?

2.  WhatarethreewaysthatΔSwillbecomepositive?

3.  DefineGibbsFreeEnergy4.  WhatistheequationforGibbsFreeEnergy?

5.  UnderwhatΔHandΔSconditionswillΔGalwaysbepositive?

Chemistry Day 76 Tuesday, April 23rd – Wednesday, April 24th,

2019

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

Kinetics: Rates of Reaction

Recall

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?

Doallreactionsoccuratthesamerate?

ReactionRates•  ChemicalKinetics=Thestudyofthespeedwithwhichreactantsareconvertedtoproducts

ReactionRates•  ReactionRate=Thechangeinconc’ofareactantorproductperunitoftime

Aretherefactorsthataffecttherateofthereaction?

Collision Theory

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

Collision Theory

Energy Diagrams

Energy Diagrams •  Recall: we can diagram a reaction’s energy vs.

progress

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 greater the Ea, the slower the reaction.

Energy Diagrams •  The peak represents a high energy transition

state (called the activated complex ). Bonds are breaking/forming before the final products are made.

Collision Theory

Factors That Affect Rxn Rate

64

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

Surface Area of Reactants

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.

CW • KineticsWSA• Study!

Chemistry Day 77 Thursday, April 25th – Friday, April 26th, 2019

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

Kinetics: Rate Laws

Recall

Collision Theory

Activation Energy

Factors That Affect Rxn Rate 1. Temperature 2. Surface Area 3. Concentration 4. Presence of a Catalyst

ReactionRates•  ReactionRate=Thechangeinconcentrationofareactantorproductperunitoftime

ReactionRate•  Asareactionproceedsovertime,theconcentrationofthereactantdecreases,andtheconcentrationofaproductincreases.

RateLaws•  Ratestypicallydecreaseasreactantconcentrationsdecrease– Fewerreactantmolecules=fewerinteractions/collisions

•  Thismakesitdifficulttomeasurerates,astheyareconstantlychanging,oftenfasterthanwecanmeasure

RateLaws

RateLaws•  Ratelaw=Themathematicalrelationshipbetweentherateofachemicalreactionandtheconcentrationofreactants

•  Inaratelaw,weonlylookatthereactants

TheRateLawForAàproducts

Rate=k[A]n•  k=rateconstant(constantofproportionality)•  n=reactionorder

•  Remember:bracketsrepresenttheconcentrationinMolarity,so[A]means“themolarconcentrationofA”


Rate=k[A]n•  Whatistherateconstant?•  Itisanumericalvaluethatisspecifictoagiventemperature

•  Theunitsofkvary–youmustsolveforkbypluggingintoseewhatunitsareleft!


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•  Forazeroorderreaction…•  changingtheconcentrationofreactantAhasnoeffectontheoverallrate

RateLaws•  Forafirstorderreaction…•  [A]hasadirecteffectontherate.Forexample,doubling[A]willdoubler.

RateLaws•  Forasecondorderreaction…•  changing[A]hasanexponentialeffectontherate.

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


0.20 0.015

0.40 0.015

TryThis:•  Determinetheratelawexpressionforthedatabelow:


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


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)


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


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


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/4•  Considerthereactionbetweennitrogendioxideandcarbonmonoxide:2NO(g)+Cl2(g)à2NOCl(g)

•  Fromthedata,determine:a.  Theratelawforthereactionb.  Therateconstant(k)forthereaction

[NO](M) [Cl2](M) InitialRate(M/s)

0.50 0.50 0.0190

1.00 0.50 0.0760

1.00 1.00 0.1520

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