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Chapter 17—Reaction Energy and Reaction Kinetics
MULTIPLE CHOICE
1. Which of the following is a measure of the average kinetic energy of the particles in a sample of matter?
a. chemical kinetics
c. reaction rate
b. thermochemistry
d. temperature
ANS: D
PTS: 1
3. In what units is temperature measured?
a. degrees Celsius
b. kelvins
ANS: C
PTS: 1
DIF: I
OBJ: 17-1.1
c. both degrees Celsius and kelvins
d. None of the above
DIF: I
OBJ: 17-1.1
5. The greater the kinetic energy of the particles in a sample of matter,
a. the higher the temperature is.
b. the lower the temperature is.
c. the more energy is absorbed by the sample as heat.
d. the less energy is released by the sample as heat.
ANS: A
PTS: 1
DIF: I
OBJ: 17-1.1
7. Which of the following best describes heat?
a. the energy transferred between samples of matter because of a difference in their
temperatures
b. a measure of the average kinetic energy of the particles in a sample of matter
c. the energy stored in a sample of matter
d. bond energy
ANS: A
PTS: 1
DIF: I
OBJ: 17-1.2
21. What is the energy released or absorbed as heat when one mole of a compound is produced by
combination of its elements?
a. heat of formation
c. free energy
b. heat of combustion
d. entropy
ANS: A
23.
PTS: 1
DIF: I
OBJ: 17-1.4
H = _______ .
a. Hreactants – Hproducts
c. Hproducts – Hreactants
b. Hreactants + Hproducts
d.
ANS: C
PTS: 1
DIF: I
OBJ: 17-1.4
Heats of Formation (kJ/mol)
Substance
Formula
ammonia(s)
NH3
Heats of Combustion (kJ/mol)
H0f
–45.9
Substance
Formula
hydrogen(g)
H2
H0c
–
285.8
barium nitrate(s)
Ba(NO3)2
–992.1
carbon (graphite)(s)
C
benzene(l)
C6H6
+49.1
carbon monoxide (g)
CO
–
393.5
–
283.0
calcium chloride(s)
CaCl2
–795.4
methane (g)
CH4
carbon (diamond) (s)
C
+1.9
ethane(g)
C2H6
–
890.8
–
1560.7
carbon (graphite)(s)
C
0.0
propane(g)
C3H8
carbon dioxide(g)
CO2
–393.5
butane(g)
C4H10
–
2219.2
–
2877.6
copper(II) sulfate(s)
CuSO4
–771.4
pentane(g)
–
C5H12
3535.6
ethyne (acetylene)(g)
C2H2
+228.2
hexane(l)
–
C6H14
4163.2
hydrogen chloride(g)
–92.3
HCl
heptane(l)
–
C7H16
4817.0
water(l)
–285.8
H2O
octane(l)
–
C8H18
5470.5
nitrogen dioxide(g)
NO2
+33.2
ethene (ethylene)(g)
–
C2H4
1411.2
ozone(g)
O3
+142.7
propene (propylene)(g)
–
C3H6
2058.0
sodium chloride(s)
–385.9
NaCl
ethyne (acetylene)(g)
–
C2H2
1301.1
sulfur dioxide(g)
–296.8
SO2
benzene(l)
–
C6H6
3267.6
zinc sulfate(s)
ZnSO4
–980.1
toluene(l)
–
C7H8
3910.3
31. The driving force of a reaction depends mostly on the change in
a. state or phase.
c. entropy.
b. enthalpy.
d. product type.
ANS: B
PTS: 1
DIF: I
OBJ: 17-2.1
33. Spontaneous reactions are driven by
a. decreasing enthalpy and decreasing entropy.
b. decreasing enthalpy and increasing entropy.
c. increasing enthalpy and decreasing entropy.
d. increasing enthalpy and increasing entropy.
ANS: B
PTS: 1
55. The equation H2(g) + I2(g)
2HI(g) is a(n)
DIF: I
OBJ: 17-2.1
a. overall reaction.
b. reaction mechanism.
ANS: A
PTS: 1
c. reaction pathway.
d. intermediate reaction.
DIF: I
OBJ: 17-3.1
57. Examining a chemical system before and after reaction reveals the
a. net chemical change.
c. intermediates.
b. reaction mechanism.
d. activated complex.
ANS: A
PTS: 1
DIF: I
OBJ: 17-3.1
59. What is the overall equation for the formation of hydrogen iodide from its elements?
a. H(g) + I(g) HI(g)
c. H(g) + I2(g) HI(g) + I(g)
b. H2(g) + I2(g) 2HI(g)
d. H2(g) + I(g) HI(g) + H(g)
ANS: B
PTS: 1
63. To react, gas particles must
a. be in the same physical state.
b. have the same energy.
ANS: D
PTS: 1
DIF: II
OBJ: 17-3.1
c. have different energies.
d. collide.
DIF: I
OBJ: 17-3.2
65. If colliding molecules have an orientation that favors reaction, they have
a. the correct angles and distances between atoms.
b. sufficient energy for each molecule.
c. speeds that are neither too fast nor too slow.
d. entropy values in the proper range.
ANS: A
PTS: 1
DIF: I
OBJ: 17-3.2
67. Raising the temperature of reactants in a system
a. increases the average kinetic energy of the molecules.
b. decreases the average kinetic energy of the molecules.
c. decreases the rate of collision of molecules.
d. has no effect on the average kinetic energy of molecules.
ANS: A
PTS: 1
DIF: I
OBJ: 17-3.2
69. Raising the temperature of gas particles
a. increases both collision energy and favorability of orientation.
b. increases neither collision energy nor favorability of orientation.
c. increases collision energy but does not increase favorability of orientation.
d. increases favorability of orientation but does not increase collision energy.
ANS: C
PTS: 1
DIF: I
OBJ: 17-3.2
71. The minimum energy required for an effective collision is called
a. energy of enthalpy.
c. free energy.
b. activation energy.
d. kinetic energy.
ANS: B
PTS: 1
DIF: I
OBJ: 17-3.2
73. How does the energy of the activated complex compare with the energies of reactants and products?
a.
b.
c.
d.
It is lower than the energy of both reactants and products.
It is lower than the energy of reactants but higher than the energy of products.
It is higher than the energy of reactants but lower than the energy of products.
It is higher than the energy of both reactants and products.
ANS: D
PTS: 1
DIF: I
OBJ: 17-3.3
77. An activated complex
a. always separates into the products.
b. always re-forms the reactants.
c. may either separate into the products or re-form the reactants.
d. always evaporates.
ANS: C
PTS: 1
DIF: I
79. What takes place in an activated complex?
a. Bonds form.
b. Bonds break.
ANS: C
PTS: 1
OBJ: 17-3.3
c. Some bonds form and other bonds break.
d. A catalyst is produced.
DIF: I
OBJ: 17-3.3
81. Which statement correctly describes the energy changes that occur when bonds form and when bonds
break?
a. Breaking bonds is endothermic, and forming bonds is exothermic.
b. Breaking bonds is exothermic, and forming bonds is endothermic.
c. Both are exothermic.
d. Both are endothermic.
ANS: A
PTS: 1
DIF: I
OBJ: 17-3.4
83. Which of the following is true in an exothermic reaction?
a. energy of products < activation energy < energy of reactants
b. energy of reactants < activation energy < energy of products
c. energy of products < energy of reactants < activation energy
d. energy of reactants < energy of products < activation energy
ANS: C
PTS: 1
DIF: I
89. Reaction rate depends upon
a. both collision frequency and efficiency.
b. average kinetic energy.
ANS: A
PTS: 1
c. collision efficiency.
d. average potential energy.
DIF: I
93. If the surface area of reactants is larger,
a. the reaction rate is generally higher.
b. the reaction rate is generally lower.
ANS: A
PTS: 1
OBJ: 17-3.4
OBJ: 17-4.2
c. the reaction rate is not affected.
d. the rate-determining step is eliminated.
DIF: I
103. Catalysts generally affect chemical reactions by
a. increasing the temperature of the system.
b. increasing the surface area of the reactants.
OBJ: 17-4.2
c. providing an alternate pathway with a lower activation energy.
d. providing an alternate pathway with a higher activation energy.
ANS: C
PTS: 1
107. The letter k in a rate law stands for
a. a proportionality constant.
b. concentration.
ANS: A
PTS: 1
109. The value of k in a rate law
a. is the same under all conditions.
b. varies with concentration.
ANS: D
PTS: 1
DIF: I
OBJ: 17-4.3
c. temperature.
d. reaction rate.
DIF: I
OBJ: 17-4.4
c. varies with time.
d. varies with temperature.
DIF: I
OBJ: 17-4.4
SHORT ANSWER
1. Explain the enthalpy change for a chemical reaction in terms of the enthalpies of its products and
reactants.
ANS:
The enthalpy change for a reaction equals the total enthalpy of the products minus the total enthalpy of
the reactants.
PTS: 1
DIF: II
OBJ: 17-2.1
2. How is a change in free energy related to changes in enthalpy and entropy?
ANS:
The change in free energy is the difference between the change in enthalpy and the product of the Kelvin
temperature and the entropy change. This relationship can be stated mathematically as G = H – T S.
PTS: 1
DIF: II
OBJ: 1