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© University of South Carolina Board of Trustees Bimolecular Rate Theory A + B products Rate =frequency of collisions( Z 0 [A][B]) fraction above activation energy Rate = k ( T ) [A][B] Experiment
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© University of South Carolina Board of Trustees Bimolecular Rate Theory A + B products Rate =frequency of collisions( Z 0 [A][B]) fraction above( e - E a / RT ) activation energy Rate = pZ 0 e - E a / RT [A][B] Theory Rate = k ( T ) [A][B] Experiment
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© University of South Carolina Board of Trustees Bimolecular Rate Theory A + B products Rate =frequency of collisions( Z 0 [A][B]) fraction above( e - E a / RT ) activation energy Rate = pZ 0 e - E a / RT [A][B] Theory Rate = k ( T ) [A][B] Experiment correct conc. dependence correct temp. dependence rates still too large
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© University of South Carolina Board of Trustees Bimolecular Rate Theory A + B products Rate =frequency of collisions( Z 0 [A][B]) fraction above( e - E a / RT ) activation energy fraction in a good orientation Rate = k ( T ) [A][B] Experiment
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© University of South Carolina Board of Trustees Bimolecular Rate Theory A + B products Rate =frequency of collisions( Z 0 [A][B]) fraction above( e - E a / RT ) activation energy fraction in a good( p ) orientation Rate = pZ 0 e - E a / RT [A][B] Theory Rate = k ( T ) [A][B] Experiment
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© University of South Carolina Board of Trustees Bimolecular Rate Theory A + B products Rate =frequency of collisions( Z 0 [A][B]) fraction above( e - E a / RT ) activation energy fraction in a good( p ) orientation Rate = pZ 0 e - E a / RT [A][B] Theory Rate = k ( T ) [A][B] Experiment good agreement with experiment
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© University of South Carolina Board of Trustees Bimolecular Rate Theory A + B products Rate =frequency of collisions( Z 0 [A][B]) fraction above( e - E a / RT ) activation energy fraction in a good( p ) orientation Rate = pZ 0 e - E a / RT [A][B] = A e - E a / RT [A][B] “Pre-exponential” Rate = k ( T ) [A][B] Experiment
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© University of South Carolina Board of Trustees Bimolecular Rate Theory A + B products Rate =frequency of collisions( Z 0 [A][B]) fraction above( e - E a / RT ) activation energy fraction in a good( p ) orientation = pZ 0 e - E a / RT [A][B] Rate = A e - E a / RT [A][B] Rate = k ( T ) [A][B] Experiment Arrhenius Equation
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© University of South Carolina Board of Trustees Chapt. 13 Kinetics Sec. 4 Arrhenius Equation ( T dependence of k )
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© University of South Carolina Board of Trustees Arrhenius Equation k ( T ) = A e - E a / RT
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© University of South Carolina Board of Trustees Arrhenius Equation k ( T ) = A e - E a / RT or ln k = ln A - ( E a / R )(1/ T )
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© University of South Carolina Board of Trustees Arrhenius Equation k ( T ) = A e - E a / RT or ln k = ln A - ( E a / R )(1/ T ) Graphing y = b + m x
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© University of South Carolina Board of Trustees Arrhenius Equation k ( T ) = A e - E a / RT or ln k = ln A - ( E a / R )(1/ T ) Graphing y = b + m x slope
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© University of South Carolina Board of Trustees Using an Arrhenius Plot Determine E a for the reaction 2NO 2 2NO + O 2
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© University of South Carolina Board of Trustees Arrhenius Plot
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© University of South Carolina Board of Trustees Using an Arrhenius Plot Determine E a for the reaction 2NO 2 2NO + O 2
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© University of South Carolina Board of Trustees Using an Arrhenius Plot Determine E a for the reaction 2NO 2 2NO + O 2
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© University of South Carolina Board of Trustees Using an Arrhenius Plot Determine E a for the reaction 2NO 2 2NO + O 2
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© University of South Carolina Board of Trustees Using an Arrhenius Plot Determine E a for the reaction 2NO 2 2NO + O 2
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© University of South Carolina Board of Trustees Arrhenius Plot
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© University of South Carolina Board of Trustees ln k = ln A - ( E a / R )(1/ T ) yy xx
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© University of South Carolina Board of Trustees Arrhenius Equation k ( T ) = A e - E a / RT or ln k = ln A - ( E a / R )(1/ T ) Graphing y = b + m x (many points)
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© University of South Carolina Board of Trustees Arrhenius Equation k ( T ) = A e - E a / RT or ln k = ln A - ( E a / R )(1/ T ) Graphing (many points) or Two-Point Formula
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© University of South Carolina Board of Trustees Activation Energy What is the activation energy for a reaction if its rate doubles when the temperature increases from 24 ºC to 36 ºC?
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© University of South Carolina Board of Trustees KineticsvsThermodynamics k ( T ) = A e - E a / RT or ln k = ln A - ( E a / R )(1/ T ) or K eq ( T ) = e - G° / RT or ln K eq = ( S° / R ) - ( H° / R )(1/ T ) or
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© University of South Carolina Board of Trustees Activation Energy Diagram G Thermodynamics Kinetics Reactants Products Transition State
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© University of South Carolina Board of Trustees Chapt. 13 Kinetics Sec. 5 Catalysts
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© University of South Carolina Board of Trustees Catalysts Catalyst: A substance that increases the rate of reaction, but is neither created nor consumed by the reaction ●Changes the activation energy ( E a ) by introducing a new mechanism ●Increases the rate ●Does not change the thermodynamics ( G or K eq )
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© University of South Carolina Board of Trustees G Thermodynamics E a Kinetics Kinetics, not Thermodynamics
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© University of South Carolina Board of Trustees Types of Catalysts Homogeneous: everything is in the same phase Heterogeneous: catalyst is a different phase (usually solid) Enzymes: large protein molecules (100’s-1000’s of atoms) that speed biochemical reactions
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