Composite Reactions & the Steady State Approximation

DECOMPOSITION OF AZOMETHANE

Review
Overall ReactionAZO → C2H6 + N2
Experimental Rate
Law (at low [AZO])		+d[N2]/dt = ka[AZO]2
Proposed Mechanism
[Azomethane Mechanism (s1)]
[Azomethane Mechanism (s2)]
[Azomethane Mechanism (s3)]
Overall Rate of
Production of
(Azomethane)*		d[AZO*]/dt = + k1[AZO]2 - k-1[AZO][AZO*] - k2[AZO*]
Overall Rate
of Production
of Nitrogen		d[N2]/dt = +k2[AZO*]
Steady State
Approximation		d[AZO*]/dt = 0

Obtaining the Steady State Concentration of (Azomethane)* - Step 3

[AZO*](k-1[AZO] + k2) = k1[AZO]2

Both sides of the equation are now divided by the term in the bracket,

(k-1[AZO] + k2)

leading to the result

[AZO*] = k1[AZO]2 / (k-1[AZO] + k2)

[AZO*] = k1[AZO]2 / (-k-1[AZO] - k2)

[AZO*](k-1[AZO] + k2) = k1[AZO]2 / (k-1[AZO] + k2)