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Rates of Reactions – Part 2

Rates of Reactions – Part 2. Factors affecting the rate of reaction. The surface area The concentration of the reactant The temperature at which the reaction is carried out The use of a catalyst The influence of light. 4. Rate of Reaction – Effect of Catalyst.

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Rates of Reactions – Part 2

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  1. Rates ofReactions – Part 2

  2. Factorsaffectingthe rate ofreaction • The surfacearea • The concentrationofthereactant • The temperatureatwhichthereactioniscarried out • The useof a catalyst • The influenceoflight

  3. 4. Rate ofReaction – EffectofCatalyst Hydrogen peroxidewater + oxygen Powderedmanganese IV oxide MnO2isaddedas a catalyst. The morefinelygroundupthemanganeseoxideisthefasterthereactiongoes. The massofthemanganeseoxideremainsthe same. Itis a catalyst.

  4. EffectofCatalyst The morecatalystyouusethefasterthereaction. The type ofcatalystyouuse will effectthereaction.

  5. Definition of a Catalyst A catalystis a substancethatincreasesthe rate of a chemicalreaction. The catalystremainschemicallyunchanged.

  6. Howdoes a cataystwork? • The provide a surface on whichothermoleculesoratomscanreact.

  7. Catalysts in Industry • Catalystsareveryusefulasyouonlyneed a smallamounttodramaticallychangethe rate of a reaction. • The catalystis not usedup so canbeusedagainandagain. • Used in theproductionofpolythene, painkillers, fertilizersandfabrics. • The processestomakethesecompounds, withoutcatalysts, wouldneedmuchmoreenergyandbemuchmorecostly.

  8. CatalyticConvertors • Used on carstoreducepollution. • Car exhaustsproduce CO, NO andunburnthydrocarbons. • The catalyticconvertorconvertsthesetolessharmfulproducts CO2, N2andwater. • The catalyticconvertorremovespollutingoxidesandcompletestheoxidationofunburnthydrocarbons.

  9. Catalytic Converters Rhodium andplatinum – preciousmetalsused

  10. Biological Catalysts • Living cells also producecatalysts, theseareproteinmoleculescalledenyzmes. • Characteristics; • Enzymes areproteins • Veryspecific – controlonlyonereaction • Temperature sensitive – stopworkingabove 45oC • pH sensitive – workbestat pH 7

  11. Enzymes in Industry • Biological washingpowdersuseenzymestoremovebiologicalstains(sweat, blood, food). • The enzymes break down protiensandfats. • Becausetheenzymesaretemperaturedependenttheyneed a washofnomorethan 40oC

  12. SurfaceCatalystsandCollisionTheory • Onemain type ofcatalystworksbyabsorbingthereactantmoleculesonto a solid surface. • This processofadsorptionbringsthereactingmoleculesclosertogether.

  13. Nickel CatalyzedHydrogenation • Finelydividednickelisusedas a catalysttoadd hydrogen tounsaturatedhydrocarbons.

  14. CollisionTheory • If a reactiononlyoccurswhenparticlescollidewiththesurfaceof a solid…. • Thenitfollowsthatthemoresurfaceareayouhave, themorecollisionsyouhave, thefasterthereactionis. • This also appliesif; • solutionsaremoreconcentrated • Gases aremorecompressed • Increasingthetemperatureincreasesthespeedtheparticlesaremovingagainincreasingtheprobabilityofcollision.

  15. ActivationEnergy • Not everycollisionproduces a reaction. • A certainamountofenergyneedstobepresentto break thebonds, EA • A catalystincreasesthe rate ofreactionbyreducingthe EA

  16. Activity • Page 216 • Exercise 7.4 on worksheet • Read aboutphotochemicalreactionsand do questions on page 218

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