© 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

© 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

© 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

© 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

© 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

© 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

© 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

© 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

© University of South Carolina Board of Trustees Chapt. 13 Kinetics Sec. 4 Arrhenius Equation ( T dependence of k )

© University of South Carolina Board of Trustees Arrhenius Equation k ( T ) = A e - E a / RT

© 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 )

© 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

© 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

© University of South Carolina Board of Trustees Using an Arrhenius Plot Determine E a for the reaction 2NO 2  2NO + O 2

© University of South Carolina Board of Trustees Arrhenius Plot

© University of South Carolina Board of Trustees Using an Arrhenius Plot Determine E a for the reaction 2NO 2  2NO + O 2

© University of South Carolina Board of Trustees Using an Arrhenius Plot Determine E a for the reaction 2NO 2  2NO + O 2

© University of South Carolina Board of Trustees Using an Arrhenius Plot Determine E a for the reaction 2NO 2  2NO + O 2

© University of South Carolina Board of Trustees Using an Arrhenius Plot Determine E a for the reaction 2NO 2  2NO + O 2

© University of South Carolina Board of Trustees Arrhenius Plot

© University of South Carolina Board of Trustees ln k = ln A - ( E a / R )(1/ T ) yy xx

© 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)

© 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

© 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?

© 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

© University of South Carolina Board of Trustees Activation Energy Diagram  G Thermodynamics Kinetics Reactants Products Transition State

© University of South Carolina Board of Trustees Chapt. 13 Kinetics Sec. 5 Catalysts

© 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 )

© University of South Carolina Board of Trustees  G Thermodynamics E a Kinetics Kinetics, not Thermodynamics

© 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