At high concentrations of [H2] the observed rate law is found to change to the form: Rate = k[NO]^2 i.e. the rate becomes independent of [H2].

1. Assess whether the two step mechanism:
H2 + 2NO → N2 + H2O + O (k1)
O + H2 → H2O (k2)
can explain this additional data.

Reexamine the mechanism:
2NO + H2 → O + H2O + N2 (slow k1)
O + H2 → H2O (k2)

2. Write the forward rates for both steps.

3. Based on these rates, would you expect the mechanism to change as [H2] increases? (Hint: look at the ratio)

4. Can this mechanism give the rate law Rate = k[NO]2 observed at high [H2]?

5. What other aspect of this two step mechanism might make it less likely to be the correct mechanism?

1. To assess whether the two-step mechanism can explain the change in the observed rate law at high concentrations of [H2], we need to consider the proposed mechanism and its reaction steps.

The proposed mechanism:
Step 1: H2 + 2NO → N2 + H2O + O (k1)
Step 2: O + H2 → H2O (k2)

2. The forward rates for both steps can be written as follows:
Step 1 forward rate = k1[H2][NO]^2
Step 2 forward rate = k2[O][H2]

3. Based on these rates, let's examine the ratio of the forward rates of the two steps:
Ratio = (Step 1 forward rate) / (Step 2 forward rate)
= (k1[H2][NO]^2) / (k2[O][H2])
= (k1 / k2) * ([H2][NO]^2) / [O]

If the [H2] is increased, the ratio of the forward rates will remain dependent on [H2], indicating that the mechanism does not change with increasing [H2].

4. Now, let's determine if this mechanism can give the rate law Rate = k[NO]^2 observed at high [H2].

From the mechanism, the slow step is Step 1:
2NO + H2 → O + H2O + N2 (slow k1)

The rate-determining step is the slowest step, and the rate law is determined from the stoichiometry of this step. As we can see, the stoichiometry of the slow step does not match the rate law observed at high [H2] (Rate = k[NO]^2), which suggests that this mechanism cannot explain the observed rate law.

5. Another aspect that suggests this mechanism may be less likely to be the correct mechanism is that the observed rate law is independent of [H2] at high concentrations. However, in the proposed mechanism, both Step 1 and Step 2 are dependent on [H2] in their respective forward rates. This discrepancy raises doubts about the validity of the mechanism.

1. To assess whether the given two-step mechanism can explain the change in rate law observed at high concentrations of [H2], we need to analyze the reaction steps and their rates.

The proposed mechanism is:
Step 1: H2 + 2NO → N2 + H2O + O (k1)
Step 2: O + H2 → H2O (k2)

2. Let's write the forward rates for both steps:
Forward rate for step 1: r1 = k1[H2][NO]^2
Forward rate for step 2: r2 = k2[O][H2]

3. Based on these rates, we can compare the ratios of the forward rates of both steps. In this case, the ratio of r1 and r2 is important because it determines the rate-determining step.

The ratio of r1 to r2 is (r1 / r2) = (k1[H2][NO]^2) / (k2[O][H2])

If the concentration of [H2] increases while the concentrations of [O] and [NO] remain constant, the ratio (r1 / r2) will change. Therefore, we would expect the mechanism to change as [H2] increases.

4. Now, let's analyze whether this mechanism can give the observed rate law Rate = k[NO]^2 at high [H2].

The given rate law Rate = k[NO]^2 suggests that the rate is independent of [H2]. However, in this proposed mechanism, the rate of the overall reaction depends on the concentration of [H2]. This implies that this mechanism cannot explain the observed rate law at high [H2].

5. Another aspect of this two-step mechanism that might make it less likely to be the correct mechanism is the rate-determining step. In the proposed mechanism, step 1 (2NO + H2 → O + H2O + N2) is considered the slow step. However, the observed rate law depends on the concentration of [NO], which suggests that step 1 is not the rate-determining step. This discrepancy raises doubts about the validity of the proposed mechanism.

In summary, the given two-step mechanism does not fully explain the additional data obtained from the observed rate law at high concentrations of [H2]. The mechanism cannot reproduce the rate law and has an inconsistency in terms of the rate-determining step, making it less likely to be the correct mechanism.