In the gas phase, the production of phosgene from chlorine and carbon monoxide i
ID: 1025637 • Letter: I
Question
In the gas phase, the production of phosgene from chlorine and carbon monoxide is assumed to proceed by the following mechanism C12 2 Cl Fast equilibrium Fast equilibrium Cl2coCI2 C 2 Cl-ki, c12 Slow Fast Overall reaction: CO + Cl2 COC12 (a) Write the rate law for this reaction. (Enter your answer using the generic rate constant k. Rate expressions take the general form: rate k, [A]a . [B]b.) chemPad Help Greek (b) Which species are intermediates? (Separate substances in a list with a comma.) chemPad Help GreekExplanation / Answer
a) In phosgene mechanism step 1,2,4 are fast so these steps can not be rate determining steps.Out of these step 3 is slow step so it is rate determining steps.
Step 1:- rate = k1 [Cl2] ------ i (fast step)
Step 2:- rate = k2 [Cl][CO], --------ii (fast step)
but Cl is an intermediate so we can not show it in rate determining steps.
From step 1; k-1 [Cl]2 = k1 [Cl2]
therefore; [Cl]2 = k1 [Cl2]/k-1
[Cl] = [k1 [Cl2]/k-1 ]1/2 put these values in eq. ii
rate = k2 [Cl][CO] = k2 [k1 [Cl2]/k-1 ]1/2 [CO] = k [Cl2]1/2 [CO]
k = k2 k1/(k-1)1/2
Step 3; rate = k3 [COCl][Cl2] -----iii (slow step)
but COCl is an intermediate so we can not show it in rate determining steps.
As we know ;k-2 [COCl] = k2 [Cl][CO]
[COCl] = k2 [Cl][CO]/k-2 suppose this is fast step.
put these values in eq. iii
rate = k3 [COCl][Cl2] ; = k3 [k2 [Cl][CO]/k-2][Cl2] ; = k[Cl][CO][Cl2] -------iv
value of [Cl] = [k1 [Cl2]/k-1 ]1/2
Hence from eq. iv we have ; rate = k [k1 [Cl2]/k-1 ]1/2[CO][Cl2]
rate = k [Cl2]3/2[CO] ; this is rate determining steps.
b) Cl and COCl are intermediates.
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