PHYSICAL CHEMISTRY IN BRIEF

CHAP. 9: CHEMICAL KINETICS [CONTENTS] 294

b) Reversibleoropposingreactions. These reactions proceed in both directions. The

simplest case is

A → R

R → A

i.e. A⇀↽R. (9.91)

c)Consecutive reactions. The reactants react to form intermediates from which the

reaction products are formed. The simplest case is

A → B

B → C

i.e. A → B → C. (9.92)

d) More complexreactions. These are the combinations of parallel, reversible and con-

secutive reactions. For example,

A

↗R^1

↘R 2 →R 3

(9.93)

is a parallel and consecutive reaction at the same time.

9.4.2 Rate of formation of a substance in simultaneous reactions

In section9.1we defined the rates of consumption and formation of a substance for one single
reaction. If a substance A reacts innchemical reactions whose rates arer 1 ,r 2 ,... ,rn, we
write for the rate of formation of the substance A (the rate of consumption of a substance is
the negatively expressed rate of formation).

rA=

dcA

dτ

=

∑n

i=1

νAiri, (9.94)

whereνAiis the stoichiometric coefficient of substance A in reactioni.