Chapter 14Study Guide

Learning Objectives:

  • List the factors that affect the rate of chemical reactions
  • Determine the rate of a reaction given time and concentration.
  • Relate the rate of formation of products and the rate of disappearance of reactants given the balanced equation for the reaction.
  • Explain the form and meaning of a rate law, including the ideas of reaction order and rate constant.
  • Determine the rate law and rate constant for a reaction from a series of experiments given the measured rates for various concentrations of reactants.
  • Apply the integrated form of a rate law to determine the concentration of a reactant at a given time.
  • Apply the relationship between the rate constant of a first order reaction and its half-life.
  • Explain how the activation energy affects a rate and be able to use the Arrhenius equation
  • Predict a rate law for a reaction having a multistep mechanism given the individual steps in the mechanism.
  • Explain the principles underlying catalysis

1.What are the units for "reaction rate"

.

2.For the following reaction, C6H14(g)  C6H6(g) + 4H2(g),P(C6H14)/t was found to be 6.2  103 atm/s.

Determine P(H2)/t for this reaction at the same time.

A. 6.2  103 atm/s B. 1.6  103 atm/s C. 2.5  102 atm/s

D. 1.6  103 atm/s E. 2.5  102 atm/s

3.For the hypothetical reaction A + 3B  2C, what is the relationship between the appearance of product C, and the disappearance of reactant B?

4.For the overall chemical reaction shown below, which one of the following statements can be rightly assumed?

2H2S(g) + O2(g)  2S(s) + 2H2O(l)

A.The reaction is third-order overall.

B.The reaction is second-order overall.

C.The rate law is, rate = k[H2S]2 [O2].

D.The rate law is, rate = k[H2S][O2].

E.The rate law cannot be determined from the information given.

5. For the hypothetical reaction A + 3B  2C, the rate should be expressed as

A. rate = [A]/t

B. rate = [C]/

C. rate = 3 ([B]/t)

D. rate = (1/2) ([C]/t)

E. rate = (1/3) ([B]/t)

6.The reaction A + 2B  products has the rate law, rate = k[A][B]3. If the concentration of B is doubled while that of A is unchanged, by what factor will the rate of reaction increase?

A. 2 B. 4 C. 6 D. 8 E. 9

7.The reaction A + 2B  products was found to have the rate law, rate = k[A] [B]2.

Predict by what factor the rate of reaction will increase when the concentration of A is doubled and the concentration of B is also doubled.

A. 2 B. 4 C. 6 D. 8 E. 9

8. What are the appropriate units for a first-order rate constant

A. M/s B. 1/M·s C. 1/s D. 1/M2·s

9.It takes 42.0 min for the concentration of a reactant in a first-order reaction to drop from 0.45 M to 0.32 M at 25C. How long will it take for the reaction to be 90% complete?

A. 13.0 min B. 86.0 min C. 137 min D. 222 min E. 284 min

10.Use the following data to determine the rate law for the reaction

2NO + H2  N2O + H2O.

Expt. # [NO]0 [H2]0Initial rate

1 0.0210.0651.46 M/min

2 0.0210.2601.46 M/min

3 0.0420.0655.84 M/min

A.rate = k[NO]

B.rate = k[NO]2

C.rate = k[NO][H2]

D.rate = k[NO]2[H2]

E.rate = k[NO]2[H2]2

11.At 25C the rate constant for the first-order decomposition of a pesticide solution is6.40  103 min1. If the starting concentration of pesticide is 0.0314 M, what concentration will remain after 62.0 min at 25C?

A. 1.14  101 M B. 47.4 M C. 8.72.0 M D. 2.11  102 M E. 2.68  102 M

12.A first-order reaction has a rate constant of 3.00  103 s1. The time required for the reaction to be 75.0% complete is ______.

A. 95.8 s B. 462 s C. 231 s D. 201 s E. 41.7 s

13.The isomerization of cyclopropane to form propene

H2C — CH2

\ /  CH3 CH = CH2

CH2

is a first-order reaction. At 760 K, 15% of a sample of cyclopropane changes to propene in 6.8 min. What is the half-life of cyclopropane at 760 K?

A.3.4  102 min

B.2.5 min

C.23 min

D.29 min

E.230 min

14.The thermal decomposition of acetaldehyde, CH3CHO  CH4 + CO, is a second-order reaction. The following data were obtained at 518C.

time, sPressure CH3CHO, mmHg

0 364

42 330

105 290

720 132

Calculate the rate constant for the decomposition of acetaldehyde from the above data.

A.2.2  103/s

B.0.70 mmHg/s

C.2.2  103/mmHg·s

D.6.7  106/mmHg·s

E.5.2  105/mmHg·s

15.For what order reaction does the half-life get longer as the initial concentration increases?

A. zeroth order

B. first order

C. second order

D. none of them because half-life is always independent of the initial concentration

16.For a second order reaction, the half-life is equal to

A. t1/2 = 0.693/k B. t1/2 = k/0.693 C. t1/2 = 1/k[A]o D. t1/2 = k E. t1/2 = [A]o/2k

17.Which one of the following changes would alter the rate constant (k) for the reaction2A + B  products?

A.increasing the concentration of A

B.increasing the concentration of B

C.increasing the temperature

D.measuring k again after the reaction has run for a while

18.The Arrhenius equation is k = A e(Ea/RT). The slope of a plot of ln k vs. 1/T is equal to

  1. k
  2. k
  3. Ea
  4. Ea /R
  5. A

19.The activation energy for the reaction CH3CO  CH3 + CO is 71 kJ/mol. How many times greater is the rate constant for this reaction at 170C than at 150C?

A. 0.40 B. 1.1 C. 2.5 D. 4.0 E. 5.0

20.The reaction C4H10 C2H6 + C2H4 has an activation energy (Ea) of 350 kJ/mol, and the Ea of the reverse reaction is 260 kJ/mol. Estimate H, in kJ/mol, for the reaction as written above.

A. 90 kJ/mol B. +90 kJ/mol C. 350 kJ/mol D. 610 kJ/molE. +610 kJ/mol

21.The activation energy for the following first-order reaction is 102 kJ/mol.

N2O5(g)  2NO2(g) + (1/2)O2(g)

The value of the rate constant (k) is 1.35  104 s1 at 35C. What is the value of k at 0C?

A. 8.2  107 s1 B. 1.9  105 s1 C. 4.2  105 s1 D. 2.2  102 s1E. none of these

22.For the chemical reaction system described by the diagram below, which statement is true?

A.The forward reaction is endothermic.

B.The activation energy for the forward reaction is greater than the activation energy for the reverse reaction.

C.At equilibrium, the activation energy for the forward reaction is equal to the activation energy for the reverse reaction.

D.The activation energy for the reverse reaction is greater than the activation energy for the forward reaction.

E.The reverse reaction is exothermic.

23.An increase in the temperature of the reactants causes an increase in the rate of reaction. The best explanation for this behavior is that as the temperature increases,

A. the concentration of reactants increases.

B. the activation energy decreases.

C. the collision frequency increases.

D. the fraction of collisions with total kinetic energy > Ea increases.

E. the activation energy increases.

24.The rate law for the reaction H2O2 + 2H+ + 2I I2 + 2H2O is rate = k[H2O2][I]. The following mechanism has been suggested.

H2O2 + I  HOI + OHslow

OH + H+ H2Ofast

HOI + H+ + I  I2 + H2Ofast

Identify all intermediates included in this mechanism.

A.H+ and I

B.H+ and HOI

C.HOI and OH

D.H+ only

E.H2O and OH

25.The gas phase reaction of nitrogen dioxide and carbon monoxide was found by experiment to be second-order with respect to NO2, and zeroth-order with respect to CO below 25C.

NO2 + CO  NO + CO2

Which one of the following mechanisms is consistent with the observed reaction order?

A. NO2 + 2CO N + 2CO2 fast

N + NO2  2NO slow

B. NO2 + 2CO  N + 2CO2 slow

N + NO2  2NO fast

C. NO2 + NO2  NO3 + NO fast

NO3 + CO  NO2 + CO2 slow

D. NO2 + NO2  NO3 + NO slow

NO3 + CO  NO2 + CO2 fast

26.Which of the following statements is false?

A. A catalyst increases the rate of the forward reaction, but does not alter the reverse rate.

B. A catalyst alters the mechanism of reaction.

C. A catalyst alters the activation energy.

D. A catalyst may be altered in the reaction, but is always regenerated.

E. A catalyst increases the rate of reaction, but is not consumed.

27.With respect to the figure to the left, which choice correctly identifies all the numbered positions?

12. 3. 4.

A. catalyst intermediate activated complex product

B. reactants activated complex intermediateproduct

C. reactants activated complex catalyst product

D. reactants intermediate activated complexproduct

E. reactants intermediate activated complexcatalyst

28.Nitrous oxide (N2O) decomposes at 600C according to the balanced equation

2N2O(g)  2N2(g) + O2(g)

A reaction mechanism involving three steps is shown below. Identify all of the catalysts in the following mechanism.

Cl2(g)  2Cl(g)

N2O(g) + Cl(g)  N2(g) + ClO(g) (occurs twice)

ClO(g) + ClO(g)  Cl2(g) + O2(g)

A. Cl B. Cl2 C. ClO D. N2O E. ClO and Cl

29.The thermal decomposition of acetaldehyde, CH3CHO  CH4 + CO, is a second-order reaction. The following data were obtained at 518C.

time, sPressure CH3CHO, mmHg

0 364

42 330

105 290

720 132

Based on the data given, what is the half-life for the disappearance of acetaldehyde?

A. 1.5  105 s B. 410 s C. 5.4  107 sD. 520 s E. 305 s

30.The isomerization of cyclopropane follows first order kinetics. The rate constant at

700 K is 6.20  104 min1, and the half-life at 760 K is 29.0 min. Calculate the activation energy for this reaction.

A.5.07 kJ/mol B. 27.0 kJ/mol C. 50.7 kJ/mol D. 160. kJ/molE.270. kJ/mol