ch15---the-effect-of-temp-and-catalyst-on-reaction-rate.ppt

5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21Chapter 15The Effect of Temperature Change and Catalyst on Reaction Rate15.1 Effect of Temperature Change on Reaction Rate in Terms of Activation Energy15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level15.3 Energy Profile 15.4 Catalysts and Their Effect on Reaction Rates5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 2215.1 Effect of Temperature Change on Reaction Rate in Terms of Activation Energy(SB p.50)Activation EnergyExothermic reactionActivation energy=energy required to break bonds(related to the rate of reaction)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 2315.1 Effect of Temperature Change on Reaction Rate in Terms of Activation Energy(SB p.50)Activation EnergyEndothermic reactionActivation energy=energy required to break bonds(related to the rate of reaction)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 2415.1 Effect of Temperature Change on Reaction Rate in Terms of Activation Energy(SB p.51)Arrhenius EquationWhere k is the reate constant of the reaction,A is a constant which is independent of temperature,e is the base of the natural logarithm,Ea is the activation energy of the reaction in J mol-1,R is the ideal gas constant(i.e.8.314 J K-1 mol-1).and T is the temperature in Kelvin.K=Ae 5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 2515.1 Effect of Temperature Change on Reaction Rate in Terms of Activation Energy(SB p.52)Determination of Activation Energy Using Arrhenius EquationIn k=In A 5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 2615.1 Effect of Temperature Change on Reaction Rate in Terms of Activation Energy(SB p.52)Determination of Activation Energy Using two rate constantsIn k1=In A .(1)In k2=In A .(2)By substracting equation(2)from equation(1),we obtain:In k1/k2=(1/T1 1/T2)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 27gasConsider a sample of gas:Do all gas molecules move at the same speed?Why is there a distribution of molecular speeds even at a fixed temperature?15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.55)Distribution of Molecular Speeds in a GasArea under curve=total no.of gas molecules5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 28RemarksWith an increase in the temperature,the most probable speed increases.Actually the square of the average speed(c2)absolute temp15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.55)Change in the most probable speed5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 29RemarksThe distribution curve becomes flattened as the temp rises fewer molecules will possess the most probable speed but there the proportion of fast moving molecules 15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.55)Increased proportion of fast-moving molecules5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 210Effective collisions=collisions between reactant particles with high enough energies&proper orientations.In terms of Activation Energy:15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.57)Simple Collision Theory5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 211In terms of Collision Orientation:A Proper Orientation15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.57)Simple Collision TheoryHCl(g)+NH3(g)NH4Cl(s)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 212Some Improper Orientations15.2 The Interpretation of Rates of Gaseous Reactions at Molecular Level (SB p.57)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21315.3 Energy Profile(SB p.59)Energy Profile/activated complex5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 214Rate=kABCRemarkThus the order of reaction is related to the mechanism15.3 Energy Profile(SB p.59)Single-stage ReactionA-B+C ABC A+B+C5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 215ExampleRate=kCH3CH2CH2CH2BrH2OThus the orders of reaction are both 1 w.r.t.CH3CH2CH2CH2Br&H2OCH3CH2CH2CH2Br+H2O CH3CH2CH2CH2OH+H+Br-15.3 Energy Profile(SB p.60)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 216The slowest stage(stage 1)is the rate determining step(RDS)The order of rx is 1 w.r.t.DEmolecularity=1molecularity=2The order of rx the molecularity of the RDS15.3 Energy Profile(SB p.61)Multi-stage Reaction Stage 1:D-E intermediate Stage 2:Intermediate+F D-F+EOverall reaction:D-E+F D-F+E Rate=kDE5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 217ExampleRate=k(CH3)3Br(CH3)3Br+H2O (CH3)3OH+H+Br-i.e.1st order w.r.t.(CH3)3Br but 0th order w.r.t.H2O15.3 Energy Profile(SB p.62)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 218A+B ABcatalystMechanism15.4 Catalysts and Their Effect on Reaction Rates(SB p.64)Catalysts and Reaction Rates Stage 1:A+catalyst A-catalyst Stage 2:A-catalyst+B A-B+catalystOverall reaction:A+B A-B5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21915.4 Catalysts and Their Effect on Reaction Rates(SB p.64)Energy profiles of the uncatalysed and catalysed pathways of a reaction5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 22015.4 Catalysts and Their Effect on Reaction Rates(SB p.64)Effect of catalyst on the fraction of particles5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 221CatalystHomogenousCatalystHeterogenousCatalyst(Reactants&catalyst are in the same phase)(Reactants&catalyst are NOT in the same phase)A phase is a part of a system in which there is a uniform distribution of particles.15.4 Catalysts and Their Effect on Reaction Rates(SB p.66)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 22215.4 Catalysts and Their Effect on Reaction Rates(SB p.65)Homogeneous Catalysis Intermediate FormationA reactive intermediate is formed.5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 22315.4 Catalysts and Their Effect on Reaction Rates(SB p.65)reactive intermediateEnergy Profile of Esterification5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 224in different phasesurface of MnO2 for adsorption of H2O2HO O H15.4 Catalysts and Their Effect on Reaction Rates(SB p.67)Heterogeneous Catalysis Adsorption2H2O2(aq)MnO2(s)as catalyst 2H2O(l)+O2(g)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 225in different phasesurface of MnO2 for adsorption of H2O2HO O H15.4 Catalysts and Their Effect on Reaction Rates(SB p.67)2H2O2(aq)MnO2(s)as catalyst 2H2O(l)+O2(g)Heterogeneous Catalysis Adsorption5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 226in different phasesurface of MnO2 for adsorption of H2O2HO O H15.4 Catalysts and Their Effect on Reaction Rates(SB p.67)Heterogeneous Catalysis Adsorption2H2O2(aq)MnO2(s)as catalyst 2H2O(l)+O2(g)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 227in different phasesurface of MnO2 for adsorption of H2O2HO O HPartial bond formationOriginal bonds weakenHeterogeneous Catalysis Adsorption2H2O2(aq)MnO2(s)as catalyst 2H2O(l)+O2(g)15.4 Catalysts and Their Effect on Reaction Rates(SB p.67)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 228Applications of CatalystsIndustrial Catalysts15.4 Catalysts and Their Effect on Reaction Rates(SB p.68)1.Iron is used in the Haber process.2.N2(g)+3H2(g)Fe 2NH3(g)2.Platinum or vanadium(V)oxide is used in the Contact process 2SO2(g)+O2(g)Pt or V2O5 2SO3(g)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 229Industrial Catalysts(triesters)Applications of Catalysts15.4 Catalysts and Their Effect on Reaction Rates(SB p.69)3.Nickel,platinium or palladium is used in the hydrogenation of unsaturated oils to make margarine.liquidsolid5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 230Industrial Catalysts15.4 Catalysts and Their Effect on Reaction Rates(SB p.69)Applications of Catalysts4.Nickel and nickel(II)oxide are used in the production of town gas in Hong Kong.C5H12(g)+5H2O(g)Ni or NiO 5CO(g)+11 H2(g)2CO(g)+2H2(g)CO2(g)+CH4(g)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 231Applications of CatalystsCatalytic Converters in Car Exhaust Systems15.4 Catalysts and Their Effect on Reaction Rates(SB p.69)2CO(g)+2NO(g)Rh 2CO2(g)+N2(g)CxHy(g)+(x+y/4)O2(g)Pt xCO2(g)+y/2 H2O(g)2CO(g)+O2(g)Pt 2CO2(g)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 232Applications of CatalystsEnzymes in Biological Catalysts15.4 Catalysts and Their Effect on Reaction Rates(SB p.69)C6H12O6(aq)yeast 2C2H5OH(aq)+2CO2(g)5/22/20245/22/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 233