Question 1

Which of the following best describes the difference between thermodynamics and kinetics for a chemical reaction?

Accepted Answer

Thermodynamics determines if a reaction is spontaneous, while kinetics determines how fast the reaction occurs.

Question 2

For the reaction $$2A \rightarrow B + 3C$$, if $$\frac{\Delta [B]}{\Delta t} = 6.0\ \mathrm{M/s}$$, what is $$\frac{\Delta [A]}{\Delta t}$$?

Accepted Answer

$$-12.0\ \mathrm{M/s}$$

Question 3

Given the rate law $$	ext{Rate} = k[A]^{1/2}[B]$$, what are the units of the rate constant $$k$$?

Accepted Answer

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

Question 4

A first-order reaction has a rate constant $$k = 0.24\ \mathrm{s}^{-1}. If $$the initial concentration of A is $$1.0\ \mathrm{M}$$, what is the concentration after 10 seconds? Use $$[A] = [A]_0 e$$^{-kt}$$.

Accepted Answer

$$0.090\ \mathrm{M}$$

Question 5

For a first-order reaction, what is the half-life ($$t_{1/2}) in $$terms of the rate constant $$k$$?

Accepted Answer

$$t_{1/2} = \frac{\ln 2}{k}$$

Question 6

A reaction has half-lives of 30 s, 60 s, and 120 s for the first three half-lives. What is the order of the reaction?

Accepted Answer

Second order

Question 7

Which plot will yield a straight line for a zero-order reaction?

Accepted Answer

$$[A] vs$$. $$t$$

Question 8

According to collision theory, what is the effect of increasing temperature on the rate constant $$k$$?

Accepted Answer

It increases $$k$$ because more molecules have enough energy to overcome $$E_a.$$

Question 9

Given the Arrhenius equation $$k = Ae$$^{-E_a/RT}$$, which of the following will increase the rate constant k$?

Accepted Answer

Increasing the frequency factor $$A$$

Question 10

A reaction has $$k_1 = 0.0125$$\ \mathrm{s}^{-1}$$ at T_1$ = 295\ \mathrm{K}$$ and $$k_2 = 0.0375$$\ \mathrm{s}^{-1}$$ at T_2$ = 325\ \mathrm{K}. $$Using $$R = 8.314\ \mathrm{J\ $$mol^{-1}$$ K$$^{-1}$$}$$, what is the activation energy $$E_a in kJ/$$mol? Use $$\ln\left(\frac{k_2$}{k_1$}\right) = \frac{E_a}{R}\left(\frac{1}{T_1$} - \frac{1}{T_2$}\right).$$

Accepted Answer

$$29.2\ \mathrm{kJ/mol}$$

Question 11

Which of the following statements about catalysts is TRUE?

Accepted Answer

A catalyst provides an alternate pathway with lower activation energy.

Question 12

In the reaction mechanism below, which species is an intermediate?
NO$$_2 + NO$_2$$ $$\rightarrow NO$_3 + NO ($$slow)
NO$$_3 + CO$$ $$\rightarrow NO$_2 + CO$_2 ($$fast)

Accepted Answer

NO$$_3$$

Question 13

For the reaction $$2	ext{NO} + 	ext{Cl}_2 ightarrow 2	ext{NOCl}$$, the rate law is found to be $$	ext{Rate} = k[	ext{NO}]^2[	ext{Cl}_2]^2. $$What is the overall order of the reaction?

Accepted Answer

4

Question 14

Which of the following is a correct rate law for an elementary reaction: $$A + 2B \rightarrow$$ products?

Accepted Answer

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

Question 15

For the decomposition of ozone $$2	ext{O}_3 (g) ightarrow 3	ext{O}_2 (g)$$, the experimentally observed rate law is $$	ext{Rate} = k[	ext{O}_3]^2/[	ext{O}_2]. If$$ $$[	ext{O}_2] is $$doubled while $$[	ext{O}_3]$$ remains constant, what happens to the rate?

Accepted Answer

The rate decreases by a factor of 2.

Question 16

Which of the following is NOT a requirement for a valid reaction mechanism?

Accepted Answer

The mechanism must have only one step.

Question 17

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

Accepted Answer

It lowers the activation energy ($$E_a) $$but does not change the energy of reactants or products.

Question 18

In a multi-step reaction, which step determines the overall rate law?

Accepted Answer

The slowest step

Question 19

Which of the following is true about the half-life of a first-order reaction?

Accepted Answer

It is constant for all concentrations.

Question 20

Which of the following is a real-world example of a catalyst speeding up a reaction?

Accepted Answer

Iron in the Haber process for ammonia synthesis

Chemical Kinetics: Reaction Rates, Mechanisms, and Catalysis

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