Questions: Question 7 1 pts A proposed mechanism for the reduction of nitrogen as NO by hydrogen is: Step 1 (slow): H2(g) + 2 NO(g) -> N2O(g) + H2O(g) Step 2 (fast): N2O(g) + H2(g) -> N2(g) + H2O(g) If the proposed mechanism is correct, which of the following statements is NOT true? - the activation energy for step 2 probably less than that of step 1 - the reaction rate is second order in NO - N2O is the transition state - the reaction rate is probably the first order in H2 - the energy diagram for this reaction has two maxima

Question 7
1 pts

A proposed mechanism for the reduction of nitrogen as NO by hydrogen is:

Step 1 (slow):
H2(g) + 2 NO(g) -> N2O(g) + H2O(g)

Step 2 (fast):
N2O(g) + H2(g) -> N2(g) + H2O(g)

If the proposed mechanism is correct, which of the following statements is NOT true?
- the activation energy for step 2 probably less than that of step 1
- the reaction rate is second order in NO
- N2O is the transition state
- the reaction rate is probably the first order in H2
- the energy diagram for this reaction has two maxima

Transcript text: Question 7 1 pts A proposed mechanism for the reduction of nitrogen as NO by hydrogen is: Step 1 (slow): \[ \mathrm{H}_{2}(\mathrm{~g})+2 \mathrm{NO}(\mathrm{~g}) \longrightarrow \mathrm{N}_{2} \mathrm{O}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \] Step 2 (fast): \[ \mathrm{N}_{2} \mathrm{O}(\mathrm{~g})+\mathrm{H}_{2}(\mathrm{~g}) \longrightarrow \mathrm{N}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \] If the proposed mechanism is correct, which of the following statements is NOT true? the activation energy for step 2 probably less than that of step 1 the reaction rate is second order in NO $\mathrm{N}_{2} \mathrm{O}$ is the transition state the reaction rate is probably the first order in $\mathrm{H}_{2}$ the energy diagram for this reaction has two maxima

Solution

Solution Steps

Step 1: Analyze the Mechanism

The given mechanism consists of two steps:

Step 1 (slow): $\mathrm{H}_{2}(\mathrm{~g})+2 \mathrm{NO}(\mathrm{~g}) \longrightarrow \mathrm{N}_{2} \mathrm{O}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g})$
Step 2 (fast): $\mathrm{N}_{2} \mathrm{O}(\mathrm{~g})+\mathrm{H}_{2}(\mathrm{~g}) \longrightarrow \mathrm{N}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g})$

The slow step is the rate-determining step, which means the overall reaction rate is determined by this step.

Step 2: Determine the Rate Law

For the rate-determining step (Step 1), the rate law can be written as: \[ \text{Rate} = k[\mathrm{H}_2][\mathrm{NO}]^2 \]

This indicates that the reaction is second order in $\mathrm{NO}$ and first order in $\mathrm{H}_2$.

Step 3: Evaluate Each Statement

The activation energy for step 2 is probably less than that of step 1: This is likely true because step 2 is fast, suggesting a lower activation energy compared to the slow step 1.
The reaction rate is second order in NO: This is true, as derived from the rate law of the slow step.
$\mathrm{N}_{2} \mathrm{O}$ is the transition state: This is not true. $\mathrm{N}_{2} \mathrm{O}$ is an intermediate, not a transition state. Transition states are not typically isolated or stable species.
The reaction rate is probably first order in $\mathrm{H}_{2}$: This is true, as derived from the rate law of the slow step.
The energy diagram for this reaction has two maxima: This is true, as there are two steps, each with its own transition state, leading to two maxima in the energy diagram.