Q: A reaction has a rate constant $$k = 0.25\ \mathrm{M$$^{-1}$$ s$$^{-1}$$}$$ and an initial concentration $$[A]_0 = 0.80\ \mathrm{M}. $$What is the half-life for this second-order reaction?

$$t_{1/2} = \frac{1}{k[A]_0} = \frac{1}{0.25 \times 0.80} = 5\ \mathrm{s}$$

Question 1

Which of the following factors will NOT increase the rate of a chemical reaction?

Accepted Answer

Decreasing the temperature

Question 2

For the reaction $$\mathrm{H_2$(g) + I_2$(g) \rightarrow 2HI(g)}$$, which of the following correctly expresses the rate in terms of the change in concentration of each species?

Accepted Answer

$$\mathrm{rate = -\frac{\Delta [H_2$]}{\Delta t} = -\frac{\Delta [I_2$]}{\Delta t} = \frac{1}{2}\frac{\Delta [HI]}{\Delta t}}$$

Question 3

Given the following data for the reaction $$A \rightarrow$$ products:

| [A] (M) | Initial Rate (M/s) |
|---|---|
| 0.10 | 0.015 |
| 0.20 | 0.030 |
| 0.40 | 0.060 |

What is the order of the reaction with respect to A?

Accepted Answer

First order

Question 4

A reaction has the rate law $$\mathrm{rate = k[A]^2[B]}. $$What are the units of the rate constant $$k$$?

Accepted Answer

$$\mathrm{M$$^{-2}$$ s$$^{-1}$$}$$

Question 5

Which of the following statements about the half-life ($$t_{1/2}) of a $$first-order reaction is correct?

Accepted Answer

It is constant and independent of the initial concentration.

Question 6

For a reaction with the integrated rate law $$\ln [A]_t = -kt + \ln [A]_0$$, what is the order of the reaction?

Accepted Answer

First order

Question 7

A reaction has a rate constant $$k = 0.25\ \mathrm{M$$^{-1}$$ s$$^{-1}$$}$$ and an initial concentration $$[A]_0 = 0.80\ \mathrm{M}. $$What is the half-life for this second-order reaction?

Accepted Answer

$$t_{1/2} = \frac{1}{k[A]_0} = \frac{1}{0.25 	imes 0.80} = 5\ \mathrm{s}$$

Question 8

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

Accepted Answer

It provides an alternative pathway with a lower activation energy.

Question 9

The Arrhenius equation is $$k = Ae$$^{-E_a/RT}$$. If the activation energy E_a$ increases, what happens to the rate constant k$ at a fixed temperature?

Accepted Answer

k decreases

Question 10

For the reaction $$2H_2O_2 \rightarrow 2H_2O + O_2$, if the rate of appearance of O_2$ is 0.0014$$\ \mathrm{M/s}$$, what is the rate of disappearance of H_2O_2$?

Accepted Answer

$$0.00070\ \mathrm{M/s}$$

Question 11

Which of the following is true about the rate-determining step in a reaction mechanism?

Accepted Answer

It is the slowest step.

Question 12

A reaction has the following mechanism:
Step 1: $$A + B \rightarrow C ($$slow)
Step 2: $$C \rightarrow D ($$fast)
What is the rate law for the overall reaction?

Accepted Answer

$$\mathrm{rate = k[A][B]}$$

Question 13

Which of the following is NOT a requirement for an effective collision according to the collision theory?

Accepted Answer

Presence of a catalyst

Question 14

Given the following data for the decomposition of $$SO_2Cl_2$$:

| Time (s) | [SO2Cl2] (M) |
|---|---|
| 0 | 0.100 |
| 100 | 0.0971 |
| 200 | 0.0944 |
| 300 | 0.0917 |
| 400 | 0.0890 |

Which plot would be linear if the reaction is first order?

Accepted Answer

A plot of $$\ln [SO_2Cl_2] vs. $$time

Question 15

Which of the following best describes a bimolecular elementary step?

Accepted Answer

A step involving the collision of two reactant molecules

Question 16

For the reaction $$O_3(g) + O(g$$) \rightarrow 2O_2(g)$$, the activation energy for the forward reaction is 19$$\ \mathrm{kJ}$$ and $$\Delta H = -392\ \mathrm{kJ}$$. What is the activation energy for the reverse reaction?

Accepted Answer

$$411\ \mathrm{kJ}$$

Question 17

Which of the following is a correct statement about the effect of temperature on reaction rate?

Accepted Answer

Increasing temperature increases the fraction of molecules with energy greater than $$E_a.$$

Question 18

Which of the following is true for a zero-order reaction?

Accepted Answer

The rate is independent of the concentration of reactant.

Question 19

Which of the following is a real-world application of chemical kinetics?

Accepted Answer

Optimizing the shelf life of pharmaceuticals

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