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Chemical Kinetics

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Chemical Kinetics Chemistry, The Central Science, Chapter 14, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Chemical Kinetics John D. Bookstaver St. Charles Community College St. Peters, MO ã 2006, Prentice Hall, Inc. Chemical Kinetics ã Modified by S.A. Green, 2006 Kinetics • Studies the rate at which a chemical process occurs. • Besides information about the speed at which reactions occur, kinetics also sheds light on the reaction mechanism (exactly how the reaction occurs). Chemical Kinetics Outline: Kinetics Reaction Rates How we measure rates. How the rate depends on amounts Rate Laws of reactants. How to calc amount left or time to Integrated Rate Laws reach a given amount. How long it takes to react 50% of Half-life reactants. Arrhenius Equation How rate constant changes with T. Link between rate and molecular Mechanisms scale processes. Chemical Kinetics Factors That Affect Reaction Rates • Concentration of Reactants Ø As the concentration of reactants increases, so does the likelihood that reactant molecules will collide. • Temperature Ø At higher temperatures, reactant molecules have more kinetic energy, move faster, and collide more often and with greater energy. • Catalysts Ø Speed rxn by changing mechanism. Chemical Kinetics Reaction Rates Rxn Movie Rates of reactions can be determined by monitoring the change in concentration of either reactants or products as a function of time. [A] vs t Chemical Kinetics 2 1. Introduction ! "#$%&'()!*$('+&,-!.&-$+&'/!0$()/!1&+#!+#$!*(+$/!,2!'#$%&'()!3*,'$//$/4!!!5-6!'#$%&'()!3*,'$//!%(6! 7$!7*,.$-!0,1-!&-+,!(!/$89$-'$!,2!,-$!,*!%,*$!/&-:)$;/+$3!3*,'$//$/!.-,1-!$&+#$*!(/!elementary processes<!elementary reactions<!,*!elementary steps4!!=)$%$-+(*6!*$('+&,-/!9/9())6!&->,)>$!$&+#$*! 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B#$*$!&/!,-$!/)&:#+!',%3)&'(+&,-!+,!,9*!0$2&-&+&,-!,2!+#$!*$('+&,-!*(+$!/,!2(*<!1#&'#!&/!+,!0,!1&+#!+#$! /+,'#&,%$+*6! ,2! +#$! *$('+&,-4! ! B#$! /+,&'#&,%$+*6! /&%3)6! *$2$*/! +,! +#$! -9%7$*! ,2! %,)$/! ,2! $('#! *$('+(-+!(-0!3*,09'+!(33$(*&-:!&-!+#$!*$('+&,-!$89(+&,-4!!P,*!$A(%3)$<!+#$!*$('+&,-!$89(+&,-!2,*! +#$!1$));.-,1-!D(7$*!3*,'$//<!9/$0!&-09/+*&())6!+,!3*,09'$!(%%,-&(<!&/H! ! Reaction Rates !!!!!QC4H9Cl(aqI)!R!KD + H2OI(!!l) ! !!IQDC4H9OHK!(aq) + HCl(aq) ! [C H Cl] M 4 9 In this reaction, the QI!#(/!(!/+,'#&,%$+*&'!',$22&'&$-+!,2!F<!DI!#(/!(!',$22&'&$-+!,2!K<!(-0!QDconcentration of K!#(/!(!',$22&'&$-+!,2!I4!! C$!',9)0!0$+$*%&-$!+#$!*(+$!,2!+#&/!*$('+&,-!&-!(-6!,-$!,2!+#*$$!1(6/<!76!%,-&+,*&-:!+#$!'#(-:&-:!butyl chloride, C4H9Cl, was measured at various times, t. Chemical Kinetics 2 1. Introduction ! "#$%&'()!*$('+&,-!.&-$+&'/!0$()/!1&+#!+#$!*(+$/!,2!'#$%&'()!3*,'$//$/4!!!5-6!'#$%&'()!3*,'$//!%(6! 7$!7*,.$-!0,1-!&-+,!(!/$89$-'$!,2!,-$!,*!%,*$!/&-:)$;/+$3!3*,'$//$/!.-,1-!$&+#$*!(/!elementary processes<!elementary reactions<!,*!elementary steps4!!=)$%$-+(*6!*$('+&,-/!9/9())6!&->,)>$!$&+#$*! (!/&-:)$!*$('+&>$!',))&/&,-!7$+1$$-!+1,!%,)$'9)$/<!1#&'#!1$!*$2$*!+,!(/!(!(!bimolecular!/+$3<!,*! 0&//,'&(+&,-?&/,%$*&/(+&,-!,2!(!/&-:)$!*$('+(-+!%,)$'9)$<!1#&'#!1$!*$2$*!+,!(/!(!unimolecular!/+$34!! @$*6! *(*$)6<! 9-0$*! ',-0&+&,-/! ,2! $A+*$%$)6! #&:#! 3*$//9*$<! (! termolecular!/+$3!%(6!,''9*<!1#&'#! &->,)>$/!/&%9)+(-$,9/!',))&/&,-!,2!+#*$$!*$('+(-+!%,)$'9)$/4!!5-!&%3,*+(-+!3,&-+!+,!*$',:-&/$!&/!+#(+! %(-6!*$('+&,-/!+#(+!(*$!1*&++$-!(/!(!/&-:)$!*$('+&,-!$89(+&,-!&-!('+9()!2('+!',-/&/+!,2!(!/$*&$/!,2! $)$%$-+(*6! /+$3/4! ! B#&/! 1&))! 7$',%$! $A+*$%$)6! &%3,*+(-+! (/! 1$! )$(*-! %,*$! (7,9+! +#$! +#$,*6! ,2! '#$%&'()!*$('+&,-!*(+$/4! ! 5/! (! :$-$*()! *9)$<! $)$%$-+(*6! 3*,'$//$/! &->,)>$! 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(/! &*,-! *9/+&-:<! +,! $A+*$%$)6! 2(/+! *$('+&,-/<! /9'#! (/! +#$! $)$'+*,-! +*(-/2$*! 3*,'$//$/! &->,)>$0! &-! %(-6! 7&,),:&'()! /6/+$%/! ,*! +#$! ',%79/+&,-! *$('+&,-/!,''9**&-:!&-!2)(%$/4! !! 5!/+906!&-+,!+#$!.&-$+&'/!,2!(!'#$%&'()!*$('+&,-!&/!9/9())6!'(**&$0!,9+!1&+#!,-$!,*!7,+#!,2!+1,!%(&-! :,()/!&-!%&-0H! ! !F4!5-()6/&/!,2!+#$!/$89$-'$!,2!$)$%$-+(*6!/+$3/!:&>&-:!*&/$!+,!+#$!,>$*())!*$('+&,-4!!&4$4! !!+#$!reaction mechanism4! ! !I4!J$+$*%&-(+&,-!,2!+#$!(7/,)9+$!*(+$!,2!+#$!*$('+&,-!(-0?,*!&+/!&-0&>&09()!$)$%$-+(*6! !!/+$3/4! ! B#$!(&%!,2!+#&/!',9*/$!&/!+,!/#,1!6,9!#,1!+#$/$!+1,!:,()/!%(6!7$!('#&$>$04! ! ! 2. Rate of reaction C#$-!1$!+().!(7,9+!+#$!*(+$!,2!(!'#$%&'()!*$('+&,-<!1#(+!1$!%$(-!&/!+#$!*(+$!(+!1#&'#!*$('+(-+/! (*$!9/$0!93<!,*!$89&>()$-+)6!+#$!*(+$!(+!1#&'#!3*,09'+/!(*$!2,*%$04!!B#$!*(+$!+#$*$2,*$!#(/!9-&+/!,2! ',-'$-+*(+&,-!3$*!9-&+!+&%$<!%,)!0%;K!/;F!L2,*!:(/!3#(/$!*$('+&,-/<!()+$*-(+&>$!9-&+/!,2!',-'$-+*(+&,-! (*$! ,2+$-! 9/$0<! 9/9())6! 9-&+/! ,2! 3*$//9*$! M! B,**<!%7(*!,*!N(O4!!B,!%$(/9*$!(!*$('+&,-!*(+$<!1$! /&%3)6!-$$0!+,!%,-&+,*!+#$!',-'$-+*(+&,-!,2!,-$!,2!+#$!*$('+(-+/!,*!3*,09'+/!(/!(!29-'+&,-!,2!+&%$4!! B#$*$!&/!,-$!/)&:#+!',%3)&'(+&,-!+,!,9*!0$2&-&+&,-!,2!+#$!*$('+&,-!*(+$!/,!2(*<!1#&'#!&/!+,!0,!1&+#!+#$! /+,'#&,%$+*6! ,2! +#$! *$('+&,-4! ! B#$! /+,&'#&,%$+*6! /&%3)6! *$2$*/! +,! +#$! -9%7$*! ,2! %,)$/! ,2! $('#! *$('+(-+!(-0!3*,09'+!(33$(*&-:!&-!+#$!*$('+&,-!$89(+&,-4!!P,*!$A(%3)$<!+#$!*$('+&,-!$89(+&,-!2,*! +#$!1$));.-,1-!D(7$*!3*,'$//<!9/$0!&-09/+*&())6!+,!3*,09'$!(%%,-&(<!&/H! ! Reaction Rates !!!!!QC4H9Cl(aqI) !R!KD+ H2O(Il)!! ! !!IQDC4H9OHK!(aq) + HCl(aq) ! Average Rate, M/s The average rate of QI!#(/!(!/+,'#&,%$+*&'!',$22&'&$-+!,2!F<!DI!#(/!(!',$22&'&$-+!,2!K<!(-0!QDthe reaction over K!#(/!(!',$22&'&$-+!,2!I4!! C$!',9)0!0$+$*%&-$!+#$!*(+$!,2!+#&/!*$('+&,-!&-!(-6!,-$!,2!+#*$$!1(6/<!76!%,-&+,*&-:!+#$!'#(-:&-:!each interval is the change in concentration divided by the change in time: Chemical Kinetics 2 1. Introduction ! 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