PHYSICAL CHEMISTRY IN BRIEF

CHAP. 9: CHEMICAL KINETICS [CONTENTS] 302

Obr.9.4:Time dependence of the reactants concentrations in the consecutive reaction A → B→
C.

9.4.9.3 Integrated forms of the kinetic equations.

cA = cA0e−k^1 τ, (9.131)

cB =

k 1

k 2 −k 1

cA0

[

e−k^1 τ−e−k^2 τ

]

, (9.132)

cC = cA0−cA−cB=cA0

(

1 +

k 1

k 2 −k 1

e−k^2 τ−

k 2

k 2 −k 1

e−k^1 τ

)

. (9.133)

Substance B is the intermediate of the reaction. Its concentration first increases with time
and then decreases [see Figure 9.4]. It acquires its maximum valuecB,maxat timeτmax, where

cB,max=cA0

(

k 1

k 2

)kk 2

2 −k 1

, τmax=

ln (k 2 /k 1 )

k 2 −k 1

. (9.134)

The time dependence of the substances A, B and C is illustrated in Figure9.4.