Chemistry Day 70 Monday, May 4th, 2020

Do-Now: “Kinetics CN A” 1.  Write down today’s FLT: I will be able to

identify four factors that influence the rate of a chemical reaction by completing Kinetics Notes Part A

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.

Planner: •  FinishWSandstudy!Flashcardsrecommended

Table of Contents #3: 2.  Kinetics CN Part A 3.  Kinetics WS A

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

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

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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

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Check-In 1.  Definetheterm“reactionrate”2.  Whatarefourfactorsthataffectrxn

rate?3.  Explainhowtemperatureaffectsthe

reactionrate.Bespecific.4.  Notallreactantsformproducts.What

doescollisiontheorytellusaboutwhichreactantsareabletoformproducts?

5.  Defineactivationenergyandhowcatalystscanaffectit.

HW • KineticsWSA• Study!