Q: A reaction is found to be first order in $\mathrm{A}$ and second order in $\mathrm{B}$. Which of the following could be the rate law for this reaction?

$\text{Rate} = k[\mathrm{A}][\mathrm{B}]^2$

Question 1

According to the collision model, which of the following is necessary for a chemical reaction to occur between two molecules?

Accepted Answer

The molecules must collide with enough energy and the correct orientation.

Question 2

Which of the following best explains why increasing the temperature increases the rate of a chemical reaction?

Accepted Answer

A greater fraction of molecules have kinetic energy greater than the activation energy.

Question 3

Given the Arrhenius equation $k = A e^{-E_a/(RT)}$, what does the frequency factor $A$ represent?

Accepted Answer

The frequency of collisions with the correct orientation.

Question 4

A reaction has an activation energy of $50\ \mathrm{kJ/mol}$. If the temperature is increased, what happens to the rate constant $k$?

Accepted Answer

The rate constant $k$ increases.

Question 5

Which of the following statements about catalysts is TRUE?

Accepted Answer

A catalyst provides a different pathway for the reaction with a lower activation energy.

Question 6

For the reaction $2\ \mathrm{NO} + 2\ \mathrm{H}_2 \rightarrow \mathrm{N}_2 + 2\ \mathrm{H}_2\mathrm{O}$, which of the following could be an intermediate in a proposed mechanism?

Accepted Answer

$\mathrm{N}_2\mathrm{O}_2$

Question 7

Which of the following best describes the rate-determining step in a reaction mechanism?

Accepted Answer

It is the slowest step in the mechanism.

Question 8

A reaction is found to be first order in $\mathrm{A}$ and second order in $\mathrm{B}$. Which of the following could be the rate law for this reaction?

Accepted Answer

$	ext{Rate} = k[\mathrm{A}][\mathrm{B}]^2$

Question 9

Which of the following is a correct statement about reaction intermediates?

Accepted Answer

They are produced in one step and consumed in a later step of the mechanism.

Question 10

Which of the following is a real-world example of a heterogeneous catalyst?

Accepted Answer

A metal surface used in the hydrogenation of ethene ($\mathrm{C}_2\mathrm{H}_4$) to ethane ($\mathrm{C}_2\mathrm{H}_6$).

Question 11

Given the following data for a reaction:

$\begin{align*}
T_1 &= 486^\circ\mathrm{C},\ k_1 = 1.05 	imes 10^{-3}\ \mathrm{M}^{-1/2}\mathrm{s}^{-1} \
T_2 &= 563^\circ\mathrm{C},\ k_2 = 2.14 	imes 10^{-2}\ \mathrm{M}^{-1/2}\mathrm{s}^{-1}
\end{align*}$

Use the two-point Arrhenius equation to solve for the activation energy $E_a$.

Accepted Answer

$E_a = \dfrac{R \ln(k_2/k_1)}{1/T_1 - 1/T_2}$

Question 12

Which of the following statements about enzymes is FALSE?

Accepted Answer

Enzymes are consumed during the reaction.

Question 13

Which of the following best describes the effect of a catalyst on the energy diagram of a reaction?

Accepted Answer

It lowers the activation energy but does not change the overall energy change ($\Delta E$).

Question 14

Which of the following is NOT a way that a catalyst can increase the rate of a reaction?

Accepted Answer

By increasing the activation energy required for the reaction.

Question 15

Which of the following is true about the rate law for an elementary reaction?

Accepted Answer

It can be written directly from the balanced equation for that step.

Question 16

A proposed mechanism for a reaction does NOT match the experimentally determined rate law. What does this indicate?

Accepted Answer

The proposed mechanism is incorrect.

Question 17

Which of the following best explains why termolecular elementary reactions are rare?

Accepted Answer

The probability of three molecules colliding simultaneously with the correct orientation is very low.

Question 18

Which of the following is a correct statement about the effect of a catalyst on a reversible reaction?

Accepted Answer

A catalyst speeds up both the forward and reverse reactions.

Chemical Kinetics: Temperature, Rate, Mechanisms, and Catalysis

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