Mechanisms: 2nd step

Question

The following mechanism for the gas phase reaction of nitrogen dioxide with carbon monoxide at temperatures above 225 ^oC is consistent with the observed rate law.

.....step 1.....fast:......NO₂ + CO  ONOCO

.....step 2.....slow:....ONOCO  NO + CO₂

(1) What is the equation for the overall reaction? Use the smallest integer coefficients possible. If a box is not needed, leave it blank.

+

+

(2) Enter the formula of any species that acts as a reaction intermediate? If none leave box blank:

(3) Complete the rate law for the overall reaction that is consistent with this mechanism.

Use the form k[A]^m[B]ⁿ... , where '1' is understood (so don't write it if it's a '1') for m, n etc.

Rate =

Answer 1

....step 1.....fast:......NO₂ + CO <==>  ONOCO

.....step 2.....slow:....ONOCO ==>  NO + CO₂

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(1). NO₂ + CO ==> NO + CO₂ ... overall reaction (sum the 2 elementary steps)

(2) NONOCO is an intermediate

(3) From step 1 (fast),... k1[NO2][CO] = k2[ONOCO]

solving for [NONCO] we have

[ONOCO] = k1/k2 [NO₂][CO] ... we can now substitute this into the rate law for step 2 (slow step):

From step 2 (slow) ... rate = k3[ONOCO]

rate = k3 * k1/k2 [NO₂][CO]

rate = k' [NO₂][CO] ... complete rate law for overall reaction