6.3 Practice Problems

6.3 Practice Problems#

  1. In the following reaction, \(\ce{NO2}\) is being consumed at \(\pu{1.3e-3 mol L-1 s-1}\). (a) At what rate is it being consumed? (b) At what rate is it being produced?

\[\ce{4 NO2 + O2 -> 2 N2O5}\]

  1. The solvent methylene chloride (\(\ce{CH2Cl2}\)) reacts with bisulfide (\(\ce{HS-}\)) to form dithiomethane (\(\ce{CH2(SH)2}\)) as shown in the reaction below. This reaction is monitored by measuring the rate of production. If after \(\pu{2 min}\), appears at a rate of \(\pu{10 mmol L-1 min-1}\), what is the reaction rate at which it is being consumed?

\[\ce{CH2Cl2 + 2 HS- -> CH2(SH)2 + 2 Cl-}\]

  1. Write the rate expressions and determine the reaction order in the following reactions.

\[\begin{split} \begin{align} \ce{ 2 A &-> C\\ 2 A + B &-> C } \end{align}\end{split}\]

  1. The decomposition of hydrogen peroxide (\(\ce{H2O2}\)) is a first-order reaction, as shown in the reaction below. The rate constant for this reaction at \(\pu{20 ^\circ C}\) is \(\pu{1.8e-5 s-1}\). The starting concentration of \(\ce{H2O2}\) is \(\pu{0.75 M}\). (a) Determine the remaining concentration after \(\pu{3 h}\). (b) How long will it take for the concentration to drop to \(\pu{0.10 M}\)?

\[\ce{ 2 H2O2 -> 2 H2O + O2 }\]

  1. The decomposition of ethane (\(\ce{C2H6}\)) to methyl radicals (\(\ce{.CH3}\)) is a first-order reaction with a rate constant of \(\pu{5.36e-1 s-1}\) at \(\pu{700 ^\circ C}\). Calculate the half-life of this reaction in minutes. Answer: \(\pu{21.5 min}\)

  2. Auto-oxidation of \(\ce{Fe^2+}\) occurs when exposed to the atmosphere due to the presence of \(\ce{O2(g)}\). The table below shows the observed \(\ce{Fe^2+}\) oxidation data. Determine (a) the reaction order, (b) the rate constant for this reaction, and (c) the half-life of \(\ce{Fe^2+}\).

Time, \(\pu{min}\)

Conc, \(\pu{\mu g L-1}\)

0

500

10

320

20

200

30

130

40

80

60

35

  1. A researcher has monitored the treatment of an organic pollutant using a naturally occurring mineral compound. The table below shows the kinetics data. Determine (a) the reaction order, (b) the rate constant for this reaction, and (c) the half-life of the pollutant.

Time, \(\pu{h}\)

Conc, \(\pu{\mu mol L-1}\)

1.5

137

18

98.6

42.5

68

71.5

38.4

91.5

23.7

115

12.2

138.5

8.4