Advanced Placement Chemistry 1996 Free Response Questions

8) The reaction between NO and H₂ is believed to occur in the following three-step process.

NO + NO <===> N₂O₂ (fast)

N₂O₂ + H₂ ---> N₂O + H₂O (slow)

N₂O + H₂ ---> N₂ + H₂O (fast)

(a) Write a balanced equation for the overall reaction.

(b) Identify the intermediates in the reaction. Explain your reasoning.

(c) From the mechanism represented above, a student correctly deduces that the rate law for the reaction is rate = k[NO]²[H₂].

The student then concludes that

(1) the reaction is third-order and

(2) the mechanism involves the simultaneous collision of two NO molecules and an H2 molecule. Are conclusions (1) and (2) correct? Explain.

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