Question

The reaction described by H2(g)+I2(g)⟶2HI(g) has an experimentally determined rate law of rate=k[H2][I2] Some proposed mechanisms for this reaction are: Mechanism A (1) H2(g)+I2(g)−→k12HI(g) (one-step reaction) Mechanism B (1) I2(g)⥫⥬=k−1k12I(g) (fast, equilibrium) (2) H2(g)+2I(g)−→k22HI(g) (slow) Mechanism C (1) I2(g)⥫⥬=k−1k12I(g) (fast, equilibrium) (2) I(g)+H2(g)−→k2HI(g)+H(g) (slow) (3) H(g)+I(g)−→k3HI(g) (fast) Which of these mechanisms are consistent with the observed rate law? mechanism C mechanism B mechanism A In 1967, J. H. Sullivan showed that this reaction was dramatically catalyzed by light when the energy of the light was sufficient to break the I−I bond in an I2 molecule. Which mechanism or mechanisms are consistent with both the rate law and this additional observation? mechanism A mechanism B mechanism C

Answer 1

Answer:

The only mechanism consistent with observed rate law is mechanism A.

Mechanism A is the only consistent with the observation of J. H. Sullivan

Explanation:

In a reaction, rate law is determined by slow step of the reaction.

In mechanism A, rate law is:

rate = k₁ [H₂][I₂]

In mechanism B, rate law is:

rate = k₂ [H₂][I]²

In mechanism C, rate law is:

rate = k₂ [H₂][I]

Thus, the only mechanism consistent with observed rate law is mechanism A

Now, catalyst works in the slow-step of reaction, is the reaction is catalyzed when The I-I bond breaks, the mechanism consistent with the observation is the mechanism where the slow-step of reaction involves this bond break, again, mechanism A is the only consistent with the observation of J. H. Sullivan.