Page 106 - Elements of Chemical Reaction Engineering 3rd Edition

70 Rate Laws and Stoichiometry Chap. 3

and one of diphenyl. In this discussion we shall consider this gas-phase reac-
tion to be elementary and reversible:
kB
2C6H6 < ' C12HlO +H2
k-B
or symbolically,

The specific reaction The forward and reverse specific reaction rate constants, k, and k-, ,
be respectively, will be dejined with respect to benzene.
k17
defined w.r.t.
a particular species Benzene (B) is being depleted by the forward reaction
kB
2c6 H6 ' c,, HI0 + H2
in which the rate of disappearance of benzene is

-
rB,forward = kBCi
If we multiply both sides of this equation by -1; we obtain the expression'for
the rate of formation of benzene for the forward reaction:
rB,forward = -kBci (3-11)

For the reverse reaction between diphenyl (D) and hydrogen (H2),

Cl2HlO + H2 k-B > 2C6H6

the rate of formation of benzene is given as
YB, reverse = ~-BCDCH, (3-12)

The net rate of formation of benzene is the sum of the rates of formation from
the forward reaction [i.e., Equation (3-1 l)] and the reverse reaction [i.e., Equa-
tion (3-12)]:

rB rB, net = rB, forward + 'B, reverse

(3-13)

Multiplying both sides of Equation (3-13) by -1, we obtain the rate law for
the rate of disappearance of benzene, -rB :

Elementary
reversible
A.B
[ 2)
-r,=k CA-- (3-14)