Exercises: Mechanisms and Rate Law
A proposed mechanism for the reaction of nitrogen dioxide with carbon monoxide is: Step 1 (slow): $\text{NO}2 + \text{NO}2 \rightarrow \text{NO}3 + \text{NO}$ Step 2…
A proposed mechanism for the reaction of nitrogen dioxide with carbon monoxide is:
Step 1 (slow): $\text{NO}_2 + \text{NO}_2 \rightarrow \text{NO}_3 + \text{NO}$
Step 2 (fast): $\text{NO}_3 + \text{CO} \rightarrow \text{NO}_2 + \text{CO}_2$
(a) Write the balanced overall reaction. (b) Identify the intermediate. (c) Write the rate law predicted by this mechanism.
An elementary step has the equation $2\,\text{A} + \text{B} \rightarrow \text{C}$. Write its rate law and state its molecularity. Then explain in one or two sentences…
An elementary step has the equation $2\,\text{A} + \text{B} \rightarrow \text{C}$. Write its rate law and state its molecularity. Then explain in one or two sentences why the rate law of an elementary step can be written directly from its equation, while the rate law of an overall reaction cannot.
The decomposition of hydrogen peroxide in the presence of iodide ion is proposed to occur as follows: Step 1 (slow):…
The decomposition of hydrogen peroxide in the presence of iodide ion is proposed to occur as follows:
Step 1 (slow): $\text{H}_2\text{O}_2 + \text{I}^- \rightarrow \text{H}_2\text{O} + \text{IO}^-$
Step 2 (fast): $\text{H}_2\text{O}_2 + \text{IO}^- \rightarrow \text{H}_2\text{O} + \text{O}_2 + \text{I}^-$
Write the overall reaction, identify the catalyst and the intermediate, and write the rate law.
The reaction $2\,\text{ICl} + \text{H}2 \rightarrow \text{I}2 + 2\,\text{HCl}$ is proposed to occur by this mechanism: Step 1 (slow):…
The reaction $2\,\text{ICl} + \text{H}_2 \rightarrow \text{I}_2 + 2\,\text{HCl}$ is proposed to occur by this mechanism:
Step 1 (slow): $\text{ICl} + \text{H}_2 \rightarrow \text{HI} + \text{HCl}$
Step 2 (fast): $\text{HI} + \text{ICl} \rightarrow \text{I}_2 + \text{HCl}$
(a) Write the rate law predicted by the mechanism. (b) Give the units of $k$ if the rate is measured in $\text{M/s}$. (c) By what factor does the rate change if $[\text{ICl}]$ is tripled and $[\text{H}_2]$ is doubled?
Sofia measures the initial rate of the reaction $\text{A} + \text{B} \rightarrow \text{P}$ at a fixed temperature: | Experiment | $[\text{A}]$ (M) | $[\text{B}]$ (M) |…
Sofia measures the initial rate of the reaction $\text{A} + \text{B} \rightarrow \text{P}$ at a fixed temperature:
| Experiment | $[\text{A}]$ (M) | $[\text{B}]$ (M) | Initial rate (M/s) |
|---|---|---|---|
| 1 | 0.10 | 0.10 | $2.0 \times 10^{-3}$ |
| 2 | 0.20 | 0.10 | $4.0 \times 10^{-3}$ |
| 3 | 0.10 | 0.30 | $2.0 \times 10^{-3}$ |
Two mechanisms are proposed. Mechanism I: $\text{A} \rightarrow \text{X}$ (slow), then $\text{X} + \text{B} \rightarrow \text{P}$ (fast). Mechanism II: a single elementary step $\text{A} + \text{B} \rightarrow \text{P}$.
(a) Determine the rate law and the value of $k$ with units. (b) Decide which mechanism is consistent with the data and justify your answer.
The substitution reaction $(\text{CH}3)3\text{CBr} + \text{OH}^- \rightarrow (\text{CH}3)3\text{COH} + \text{Br}^-$ is proposed to occur in two steps: Step 1 (slow):…
The substitution reaction $(\text{CH}_3)_3\text{CBr} + \text{OH}^- \rightarrow (\text{CH}_3)_3\text{COH} + \text{Br}^-$ is proposed to occur in two steps:
Step 1 (slow): $(\text{CH}_3)_3\text{CBr} \rightarrow (\text{CH}_3)_3\text{C}^+ + \text{Br}^-$
Step 2 (fast): $(\text{CH}_3)_3\text{C}^+ + \text{OH}^- \rightarrow (\text{CH}_3)_3\text{COH}$
(a) Write the rate law and identify the intermediate. (b) Ethan doubles the concentration of $\text{OH}^-$ and keeps everything else the same. Predict the effect on the rate and explain it using the mechanism.
A mechanism for the overall reaction of species B to give E has three steps: Step 1 (slow): $\text{A} + \text{B} \rightarrow \text{C}$ Step 2 (fast):…
A mechanism for the overall reaction of species B to give E has three steps:
Step 1 (slow): $\text{A} + \text{B} \rightarrow \text{C}$
Step 2 (fast): $\text{C} + \text{B} \rightarrow \text{D}$
Step 3 (fast): $\text{D} \rightarrow \text{E} + \text{A}$
(a) Write the overall reaction and identify every catalyst and intermediate. (b) Write the rate law. (c) Malik says, "The overall equation has $2\,\text{B}$, so the rate must be $k[\text{B}]^2$." Evaluate his claim. (d) Describe, in words, how the potential energy diagram would look, and say which step has the highest activation energy.
The reaction $2\,\text{NO}2 + \text{F}2 \rightarrow 2\,\text{NO}2\text{F}$ has the experimental rate law $\text{rate} = k[\text{NO}2][\text{F}2]$ with…
The reaction $2\,\text{NO}_2 + \text{F}_2 \rightarrow 2\,\text{NO}_2\text{F}$ has the experimental rate law $\text{rate} = k[\text{NO}_2][\text{F}_2]$ with $k = 0.38\ \text{M}^{-1}\text{s}^{-1}$ at a given temperature.
Mechanism A: Step 1 (slow) $\text{NO}_2 + \text{F}_2 \rightarrow \text{NO}_2\text{F} + \text{F}$; Step 2 (fast) $\text{F} + \text{NO}_2 \rightarrow \text{NO}_2\text{F}$.
Mechanism B: one termolecular elementary step, $2\,\text{NO}_2 + \text{F}_2 \rightarrow 2\,\text{NO}_2\text{F}$.
(a) Show that both mechanisms add up to the overall reaction. (b) Predict the rate law of each mechanism and decide which one is consistent with experiment. (c) Give a reason, based on collisions, why mechanism B is unlikely even if it were consistent. (d) Calculate the rate when $[\text{NO}_2] = 0.020\ \text{M}$ and $[\text{F}_2] = 0.050\ \text{M}$.