Q: A first-order reaction has a rate constant $$k = 0.25\ \text{min}^{-1}. $$What is the half-life $$t_{1/2} of $$the reaction?

$$t_{1/2} = \dfrac{0.693}{0.25} = 2.77\ \text{min}$$

Q: Given the reaction $$2O_3(g) \rightarrow 3O_2(g)$$, if the rate of appearance of $$O_2 is$$ $$6.0 \times 10$$^{-5}$$\ \text{M/s}$$, what is the rate of disappearance of $$O_3 at $$the same instant?

$$4.0 \times 10$$^{-5}$$\ \text{M/s}$$

Q: A student is studying the decomposition of an insecticide in water at $$12^\circC. $$The reaction follows first-order kinetics with $$k = 1.45\ \text{yr}^{-1}. If $$the initial concentration is $$5.7\ \text{g/cm}^3$$, what will the concentration be after 1 year?

$$[A]_t = [A]_0 e$$^{-kt}$$ = 5.7\ e$$^{-1.45 \times 1}$$ \approx 1.32\ \text{g/cm}^3$$

Question 1

Which of the following statements best describes the role of a catalyst in a chemical reaction?

Accepted Answer

A catalyst provides an alternative pathway with lower activation energy, increasing the reaction rate without being consumed.

Question 2

For the reaction $$2NO(g) + Cl_2$(g) ightarrow 2NOCl(g)$$, experimental data shows the rate law is $$	ext{Rate} = k[NO]^2[Cl_2$]. $$What are the units of the rate constant $$k$$?

Accepted Answer

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

Question 3

A first-order reaction has a rate constant $$k = 0.25\ 	ext{min}^{-1}. $$What is the half-life $$t_{1/2} of $$the reaction?

Accepted Answer

$$t_{1/2} = \dfrac{0.693}{0.25} = 2.77\ 	ext{min}$$

Question 4

Which factor does NOT affect the rate of molecular collisions in a chemical reaction?

Accepted Answer

Color of reactants

Question 5

Given the reaction $$2O_3(g) ightarrow 3O_2(g)$$, if the rate of appearance of $$O_2 is$$ $$6.0 	imes 10$$^{-5}$$\ 	ext{M/s}$$, what is the rate of disappearance of $$O_3 at $$the same instant?

Accepted Answer

$$4.0 	imes 10$$^{-5}$$\ 	ext{M/s}$$

Question 6

Which of the following integrated rate laws corresponds to a second-order reaction?

Accepted Answer

$$\dfrac{1}{[A]_t} = kt + \dfrac{1}{[A]_0}$$

Question 7

A reaction is found to be zero order in reactant A. What will happen to the rate if the concentration of A is doubled?

Accepted Answer

The rate will remain unchanged.

Question 8

Which statement about the rate-determining step in a reaction mechanism is correct?

Accepted Answer

It is the slowest step and limits the overall reaction rate.

Question 9

For the reaction $$NO_2(g) + CO(g$$) ightarrow NO(g) + $$CO_2(g$$)$$, the experimentally determined rate law is $$	ext{Rate} = k[$$NO_2$$]^2$$. What is the overall reaction order?

Accepted Answer

Second order

Question 10

Which of the following best describes the molecularity of an elementary reaction involving two reactant molecules?

Accepted Answer

Bimolecular

Question 11

The Arrhenius equation is given by $$k = Ae$$^{-E_a/(RT)}$$. Which change will increase the rate constant k$?

Accepted Answer

Increasing the temperature $$T$$

Question 12

Which of the following is true about intermediates in a reaction mechanism?

Accepted Answer

They are produced and consumed during the reaction and do not appear in the overall equation.

Question 13

A student is studying the decomposition of an insecticide in water at $$12^\circC. $$The reaction follows first-order kinetics with $$k = 1.45\ 	ext{yr}^{-1}. If $$the initial concentration is $$5.7\ 	ext{g/cm}^3$$, what will the concentration be after 1 year?

Accepted Answer

$$[A]_t = [A]_0 e$$^{-kt}$$ = 5.7\ e$$^{-1.45 	imes 1}$$ \approx 1.32\ 	ext{g/cm}^3$$

Question 14

Which of the following is the correct rate law for the elementary reaction $$NO(g) + Cl_2$(g) \rightarrow NOCl(g) + Cl(g)$$?

Accepted Answer

$$	ext{Rate} = k[NO][Cl_2$]$$

Question 15

In a reaction mechanism, which species is classified as a catalyst?

Accepted Answer

A substance that appears in the mechanism, is present at the start and end, but is not consumed.

Question 16

For a reaction with the integrated rate law $$[A]_t = [A]_0 - kt$$, which type of reaction does this represent?

Accepted Answer

Zero-order reaction

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 the activation energy.

Question 18

A reaction mechanism consists of the following steps:
Step 1: $$NO(g) + Br_2$(g) \rightarrow $$NOBr_2$$(g) ($$fast)
Step 2: $$NOBr_2(g) + NO(g$$) \rightarrow 2NOBr(g)$$ (slow)
What is the rate law for the overall reaction?

Accepted Answer

$$	ext{Rate} = k[NO][NO]$$

Question 19

Which of the following is true about the units of the rate constant $$k$$ for a first-order reaction?

Accepted Answer

$$s^{-1}$$

Chapter 14: Chemical Kinetics – Study Notes

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