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CHEM301

 Analytical Chemistry 

Unit 3

ChemicalKinetics:Rate Laws

Integrated Rate Laws

Model for Chemical

Kinetics

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CHEM301

 Analytical Chemistry 

Chemical Kinetics

• area of chemistry concerned withreaction rates

• understand the steps by which areaction takes place

• the series of steps is called reactionmechanism

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CHEM301

 Analytical Chemistry 

Reaction Rate

• change in concentration of the reactantor product per unit time

  →   !

"#t$"#$ rate   −=

"#t$"#! =

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p. 527, Table 121

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p. 52!, "i#. 121

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CHEM301

 Analytical Chemistry 

%&'% (g) →  %&' (g) * '% (g)

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CHEM301

 Analytical Chemistry 

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CHEM301

 Analytical Chemistry 

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CHEM301

 Analytical Chemistry 

$nstantaneo%s Rate

• the rate is notconstant butdecreases with

time

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CHEM301

 Analytical Chemistry 

Rate Laws

• chemical reactions are reversible

• if the re+erse reaction is neglected,

then the reaction rate depends onlyon the concentration of the reactant

  →   !

"#t$"#$ rate   −=

"#t$"#! =

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CHEM301

 Analytical Chemistry 

Rate Laws

Conc.

     r     a      t     e

rate -k#reactant$&

k . rateconstant

/ . order of thereaction0 determined by

e/periment

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CHEM301

 Analytical Chemistry 

T'pe o( Rate Laws

• rate depends on

concentration

)i*erentialrate law

• concentration depends ontime

inte#rate)rate law

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CHEM301

 Analytical Chemistry 

+r)er o( the Rate Law

rate - k#$&

if / - 1, 2rst order: rate - k#$1

if / - %, second order: rate -k#$%if / - , 4ero order: rate - k#$

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CHEM301

 Analytical Chemistry 

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CHEM301

 Analytical Chemistry 

Metho) o( $nitial Rates

to determine the order of the reaction, start withtwo di5erent concentrations:

rate% -

k#$%/ 

rate1 -

k#$1/

sol+e for /

6 In+ol+ing a 7ingleReactant

/

1

%

%

1

#$

#$

rate

rate

   

 

 

 

=

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CHEM301

 Analytical Chemistry 

Metho) o( $nitial Rates

6 In+ol+ing a 7ingleReactante/ample:

#$, M 61 6% 63 68

Initial rate,M9s

63 6;% 16< 1688

    →  products

'R=>R: 1st order

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CHEM301

 Analytical Chemistry 

Metho) o( $nitial Rates

6 In+ol+ing a 7ingleReactante/ample:

#C?3C?'$, M 61 6% 63 68

Initial rate,M9s

6

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CHEM301

 Analytical Chemistry 

Metho) o( $nitial Rates

!6 In+ol+ing More than 'neReactant

rate - k#$!$  

o+erall order - / * y

  * !   →   products

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CHEM301

 Analytical Chemistry 

Metho) o( $nitial Rates

!6 In+ol+ing More than 'neReactante/ample:

I II III

#A%$, M 61 61 6%

#Cl'%

$, M61 68 61

Initial rate,M9s

16% / 1B3 86< / 1B3 %68 / 1B3

A% (g) %ACl'% (g)* %Cl'% (g)

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CHEM301

 Analytical Chemistry 

Metho) o( $nitial Rates

!6 In+ol+ing More than 'neReactante/ample:

I II III

#A%$, M 61 61 6%

#Cl'%

$, M61 68 61

Initial rate,M9s

16% / 1B3 86< / 1B3 %68 / 1B3

"2 -# %ACl'% (g)* %Cl'% (g)

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CHEM301

 Analytical Chemistry 

Metho) o( $nitial Rates

!6 In+ol+ing More than 'neReactante/ample:

I II III

#A%$, M 61 61 6%

#Cl'%

$, M 61 68 61

Initial rate,M9s

16% / 1B3 86< / 1B3 %68 / 1B3

A% (g) %ACl'% (g)*  2Cl+2

-#

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CHEM301

 Analytical Chemistry 

Metho) o( $nitial Rates

!6 In+ol+ing More than 'neReactant

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CHEM301

 Analytical Chemistry 

Metho) o( $nitial Rates

!6 In+ol+ing More than 'neReactant

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CHEM301

 Analytical Chemistry 

Metho) o( $nitial Rates

!6 In+ol+ing More than 'neReactant

I II III IV V

[(C?3)3C!r ], M   0.50 1.0 1.5 1.0 1.0

['?/ ], M   0.050 0.050 0.050 0.10 0.20

Initial rate, M/s 0.0050 0.010 0.015 0.010 0.010

(C?3)3C!r (a) * '?/ (a) (C?3)3C'? (a) * !r/ (a)