1. Name ___________________________________________ Date ________
Reactions and Enzymes
 Log on to www.explorelearning.com andlaunch:CollisionTheory
Leftoutside,anoldironpot can take weekstoreact withoxygeninthe airand developacoat of ironoxide,or
rust. Butgiventhe rightconditions,ironandoxygencanreact ina few seconds,aswhensteel wool isburnedin
pure oxygen.Bychangingthe conditionsinwhichreactantsmeet,the rate of the chemical reactioncanbe greatly
altered.
Observinga Chemical Reaction
1. In the Gizmo™,selectthe ANIMATION pane.Checknocatalyst,andwatch.
a. Sketchthe two reactantsand twoproductsof thisreaction.
2. Whenthe two moleculesmeet,the resultingunstablecombinedmolecule iscalledthe activatedcomplex.
In reality,thisformlastsfora tinyfractionof a second.Inthisreaction,the orientationof the two
moleculesisimportant.The reactionwill nothappenif the moleculescollideinadifferentway,asinthe
examplesbelow.
3. NowselectWithcatalyst,andwatch.A catalystis a molecule thathelpsthe reactionalong.Catalyststhat
regulate reactionsinlivingorganismsare calledenzymes.
a. Draw the shape of the catalystmolecule.
4. The part of the catalyst thatbindsto the reactantsis calledthe active site.
a. How doesthe shape of the active site relate tothe shapesof the tworeactants?
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2. 5. Catalystsare oftendescribedbythe lockandkeymodel.
a. How isa catalyst-reactantcombinationsimilartoa lockand key?____________________________
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b. Was the catalyst itself changedbythe reaction?(Circleone) Yes or No
c. Basedon whatyou see,coulditbe usedagain?(Circle one) Yes or No
6. Selectthe CONTROLSpane,andcheckthat the defaultsettingsare selected:Reactantconcentrationis1.0
mol/L,Catalystconcentrationis0.0 mol/L,Surface areaisMinimum, andTemperature is100°C. ClickPlay,
and observe the molecules.
a. Describe the motionof the blue reactantmolecules.(Circle one) Random or Orderly
b. Are all the moleculesmovingatthe same speed?(Circle one) Yes or No
c. Is the reactionhappening?(Circle one) Yes or No
d. How doyou know?______________________________________________________________
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7. ClickReset,andsetthe Temperature toitsminimumvalue,0°C.ClickPlayandobserve.
a. How doesthe molecularmotioncompare tothe motionat100°C?
(Circle One) Faster Same Slower
8. ClickReset,andplaythe simulationat200°C.
a. How doesthe movementof moleculeschange asthe temperature isincreased?
(Circle one) Faster Same Slower
b. Is the change in molecularspeedverygreat?(Circle one) Yes or No
c. How doyou thinkthisaffectsthe rate of the reaction?(Circle one) Faster Same Slower
9. ClickReset.Setthe Reactantconcentrationto2.0 mol/L,andthe Surface area to Maximum.
a. How doeschangingthe concentrationof the reactantsaffectwhatyousee inthe SIMULATION
pane?The reactants are.. . (Circle one) Double Same Half

3. b. How doesa maximumsurface areaaffectwhatyousee inthe SIMULATION pane?
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c. How manymoleculesof reactantBare exposedwhenthe surface areaismaximized?
(Circle One) All Half None
d. How manywhenitis minimized?(Circle One) 0 6 14 20
Half-Life ofa Reaction
10. ClickReset.Checkthatthe Reactant concentrationisstill 2.0mol/L,the Catalystconcentrationis0.0 mol/L,
the Surface area isMaximum,and the Temperature is200°C. ClickPlay,andobserve the reactionuntil
completion.The numberof ReactantsandProductsare talliedbelowthe simulation.
11. Selectthe GRAPHtab, and observe the linesrepresentingreactantsandproducts.If the whole graphisnot
visible,clickonthe - zoom tool to the rightof the graph.
a. How doesthe numberof reactantschange overtime? (Circle one) Increase Decrease
b. How doesthe numberof productschange? (Circle one) Increase Decrease
12. The rate of reactionisthe rate at whichthe concentrationof the productschangesina periodof time.Itis
equivalenttothe slope of the productscurve on the graph,where a steeperslope representsahigher
reactionrate.
a. Is the rate of reactionthe same as time goes on? (Circle one) Yes No
b. If not, whenisithighest?
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c. and lowest?
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d. Basedon whatyou see inthe simulation,whydoesthe rate of reactionslow downastime goesby?
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4. 13. Because the rate of a reactionchangesovertime,a betterwayto compare reactionsishalf-life.The half-life
of a reactionisthe amountof time ittakesfor half of the moleculestoreact.Selectthe TABLEtab, and
scroll throughthe values.
a. At whattime didthe percentage of reactantsfirstreach50%? ________________
14. ClickReset,andthenplaythe experimentagainthree more times,pausingwhenthe percentageof
reactantsis 50% and recordingthe half life.___________ ___________ ___________
a. How consistentwasthe half-life?
(Circle One) Same each time SometimesDifferent Differenteachtime
b. Calculate the average half-life fromyourtrials,_________.
c. Why isit importanttodo multiple trialsandaverage them?________________________________
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15. Whena chemical reactionisperformedinthe lab,billionsandbillionsof moleculesare involved.How
wouldthisaffectthe "bumpiness"of the productconcentrationvs.time graph?
(Circle one) BumpierGraph Same Graph SmootherGraph
16. Wouldyouexpectasmuch variationinthe resultsfromtrial to trial?(Circle one) More Same Less
Factors AffectingReaction Rates
17. Basedon whatyou have seensofar,write a few hypothesesinyournotes.
a. How will increasedtemperature affectthe reactionrate?(Circle one) Faster No Effect Slower
b. How will increasedconcentrationof reactantsaffectthe reactionrate?
(Circle one) Faster No Effect Slower
c. How will increasedthe surface areaaffectthe reactionrate?
(Circle one) Faster No Effect Slower
d. How will the presence of acatalystaffectthe reactionrate?
(Circle one) Faster NoEffect Slower

5. 18. Set the Reactantconcentrationto2.0 mol/L,the Catalystconcentrationto0.0 mol/L,andthe Surface area
to Maximum.Keepingthose variablesconstant,findthe average half-lifeforthe three temperaturesbelow
usingtwotrialsa piece.
19. In general,howdoestemperature affectthe rate of thisreaction?(Circle one) Faster NoEffect Slower
20. For the reactionto proceed,reactantmoleculesmustcollide withacertainamountof energy,knownasthe
activationenergy.
a. As the temperature rises,how doesthe numberof collisions abovethe activationenergychange?
(Circle one) Increase Same Decrease
21. Usingthe same procedure asthe temperature test,experimenttodetermine the effectof Reactant
concentration,Catalystconcentration,andSurface areaonthe half-lifeof the reaction.Ineachsetof
experiments,remembertokeepeveryvariable the same exceptforthe variable youare investigatingusing
the defaultsof 1.0mol/L,.15mol/L,Maximumand100o
C.
Temperature Trial 1 Trial 2 Average half-life
500
C
1000
C
2000
C
ReactantConcentration
mol/L
Trial 1 Trial 2 Average half-life
.5
1.5
2
CatalystConcentration
mol/L
Trial 1 Trial 2 Average half-life
.15
.20
.25

6. a. In a normal reaction,the reactantshave to collide atjustthe rightorientationtoreact.How doesa
catalystmake thisprocesseasier? _____________________________________________________
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a. What isthe relationshipbetweenReactantconcentrationandthe rate of the reaction(nocatalyst)?
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b. Why doyou thinkthisis?_______________________________________________________________
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c. What isthe relationshipbetweenthe Catalystconcentrationandreactionrate?
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d. Why doyou thinkthisis?_______________________________________________________________
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e. Whenis there a limittohowmuchcatalyst isactuallyhelpful?
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f. What isthe effectof Surface areaon reactionrate?_____________________________________________
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g. Why doyou thinkthisis?_______________________________________________________________
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h. Whichvariable hadthe greatesteffectonthe rate of thisreaction?
(Circle One) ReactantConcentration CatalystConcentration Temperature Surface Area
i. Explain.____________________________________________________________________________
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22. Take the quizat the endof the gizmo.Correctanswerswill become bonuspoints.
Surface Area Trial 1 Trial 2 Average half-life
Min
Max