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Rate Expression

Rate Expression. The rate expression is an equation Determined experimentally Shows dependence of rate on concentrations of reactants Rate is found whilst changing concentration of a reactant. Rate Expression. Order of Reaction. Experimental Data. Experimental Data.

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Rate Expression

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  1. RateExpression Therateexpressionisanequation Determinedexperimentally Shows dependence of rateonconcentrations of reactants Rateisfoundwhilstchangingconcentration of a reactant

  2. RateExpression

  3. Order of Reaction

  4. Experimental Data

  5. Experimental Data

  6. Order of Reaction Ifdoublingconcentration has no effectthenzeroorder (w.r.t. thatreactant) Ifdoublingconcentrationdoublesratethenfirstorder Ifdoublingconcentrationquadruplesratethenitissecondorder What are ordersfor A, B, and C on page 171? Therforewhatisrateexpression?

  7. Reading and Questions Pleasereadpages 170 to 173 Makeany notes youneed. Then try questions 1 to 7 from page 173.

  8. ReactionMechanism Mostreactionsoccur in a number of steps At eachstageonlytwoparticlescollidesuccessfully Intermediatestherforeexist Sloweststepistheratedetermingstep

  9. RatedetermingStep

  10. ReactionMechanism

  11. Unimolecularstep

  12. Bimolecular

  13. RelatingmechanismtoRateExpression See page 176, figure 618

  14. ActivationEnergy

  15. Maxwell-Boltzmanndistribution

  16. Arrhenius Equation TheActivationenergy can be determinedusinganequation The Arrhenius Equation This shows theeffect of temperatureontherateconstantfor a reaction

  17. The Arrhenius Equation

  18. Arrhenius Therateconstant, k, dependsexponentiallyonthetemperature Thisiswhytemperature has a largeeffectonreactionrate Usinglogs and rearrangingtheequation…..

  19. Arrhenius equationconvertedto…

  20. Compare to y=mx + c Whatisintercept ? Gradient ? Y and x axis ?

  21. Ea can be determinedgraphically….

  22. FindingEa So theactivationenergy can be foundbymeasuringtherate at differenttemperatures, withalltheotherconditionsunchanged and thenplotting In(rate) against 1/T (in Kelvin)

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