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MIDDLE COLLEGE HIGH SCHOOL
SCIENCE DEPARTMENT
CHEMISTRY II
MS. PARKER
UNIT IX: KINETICS AND EQUILIBRIUM PROBLEM SET
1. In each of the four beakers shown below, a 2.0-centimeter strip of magnesium ribbon reacts with
100 milliliters of HCl(aq) under the conditions shown.
In which beaker will the reaction occur at the fastest rate?
(1) A
(2) B
(3) C
(4) D
2. Given the reaction at 25°C:
7. Which event must always occur for a
Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)
chemical reaction to take place?
The rate of this reaction can be increased by
(1) formation of a precipitate
using 5.0 grams of powdered zinc instead of a
(2) formation of a gas
5.0-gram strip of zinc because the powdered
(3) effective collisions between reacting
zinc has
particles
(1) lower kinetic energy
(4) addition of a catalyst to the reaction system
(2) lower concentration
8. Given the potential energy diagram for a
(3) more surface area
chemical reaction:
(4) more zinc atoms
3. In most aqueous reactions as temperature
increases, the effectiveness of collisions
between reacting particles
(1) decreases
(3) remains the same
(2) increases
4. Based on the nature of the reactants in each
of the equations below, which reaction at 25°C
will occur at the fastest rate?
(1) C(s) + O2(g) → CO2(g)
(2) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(ℓ)
(3) CH3OH(ℓ) + CH3COOH(ℓ) →
CH3COOCH3(aq) + H2O(ℓ)
(4) CaCO3(s) → CaO(s) + CO2(g)
5. A 1.0-gram piece of zinc reacts with 5
milliliters of HCl(aq). Which of these
Which statement correctly describes the energy
conditions of concentration and temperature
changes that occur in the forward reaction?
would produce the greatest rate of reaction?
(1) The activation energy is 10. kJ and the
(1) 1.0 M HCl(aq) at 20.°C
reaction is endothermic.
(2) 1.0 M HCl(aq) at 40.°C
(2) The activation energy is 10. kJ and the
(3) 2.0 M HCl(aq) at 20.°C
reaction is exothermic.
(4) 2.0 M HCl(aq) at 40.°C
(3) The activation energy is 50. kJ and the
6. At STP, which 4.0-gram zinc sample will
reaction is endothermic.
react fastest with dilute hydrochloric acid?
(4) The activation energy is 50. kJ and the
(1) lump
(3) powdered
reaction is exothermic.
(2) bar
(4) sheet metal
1
9. Increasing the temperature increases the
rate of a reaction by
(1) lowering the activation energy
(2) increasing the activation energy
(3) lowering the frequency of effective
collisions between reacting molecules
(4) increasing the frequency of effective
collisions between reacting molecules
10. The potential energy diagram below
represents a reaction.
13. Given the reaction:
2 H2(g) + O2(g) → 2 H2O(ℓ) + 571.6 kJ
What is the approximate ∆H for the formation
of 1 mole of H2O(ℓ)?
(1) –285.8 kJ
(3) –571.6 kJ
(2) +285.8 kJ
(4) +571.6 kJ
14. Adding a catalyst to a chemical reaction
results in
(1) a decrease in activation energy and a
decrease in the reaction rate
(2) a decrease in activation energy and an
increase in the reaction rate
(3) an increase in activation energy and a
decrease in the reaction rate
(4) an increase in activation energy and an
increase in the reaction rate
15. A catalyst increases the rate of a chemical
reaction by
(1) lowering the activation energy of the
reaction
(2) lowering the potential energy of the
products
(3) raising the temperature of the reactants
(4) raising the concentration of the reactants
16. Which statement best explains the role of a
catalyst in a chemical reaction?
(1) A catalyst is added as an additional reactant
and is consumed but not regenerated.
(2) A catalyst limits the amount of reactants
used.
(3) A catalyst changes the kinds of products
produced.
(4) A catalyst provides an alternate reaction
pathway that requires less activation energy.
17. Given the balanced equation:
Which arrow represents the activation energy
of the forward reaction?
(1) A
(3) C
(2) B
(4) D
11. Based on Reference Table I, which change
occurs when pellets of solid NaOH are added to
water and stirred?
(1) The water temperature increases as
chemical energy is converted to heat energy.
(2) The water temperature increases as heat
energy is stored as chemical energy.
(3) The water temperature decreases as
chemical energy is converted to heat energy.
(4) The water temperature decreases as heat
energy is stored as chemical energy.
12. A catalyst works by
(1) increasing the potential energy of the
reactants
(2) increasing the energy released during a
reaction
(3) decreasing the potential energy of the
products
(4) decreasing the activation energy required
for a reaction
KNO3(s) + 34.89 kJ
K+(aq) + NO3–(aq)
Which statement best describes this process?
(1) It is endothermic and entropy increases.
(2) It is endothermic and entropy decreases.
(3) It is exothermic and entropy increases.
(4) It is exothermic and entropy decreases.
18. Even though the process is endothermic,
snow can sublime. Which tendency in nature
accounts for this phase change?
(1) a tendency toward greater entropy
(2) a tendency toward greater energy
(3) a tendency toward less entropy
(4) a tendency toward less energy
2
19. Systems in nature tend to undergo changes
toward
(1) lower energy and lower entropy
(2) lower energy and higher entropy
(3) higher energy and lower entropy
(4) higher energy and higher entropy
20. Given the balanced equation:
I2(s) + energy → I2(g)
As a sample of I2(s) sublimes to I2(g), the
entropy of the sample
(1) increases because the particles are less
randomly arranged
(2) increases because the particles are more
randomly arranged
(3) decreases because the particles are less
randomly arranged
(4) decreases because the particles are more
randomly arranged
21. Which of these changes produces the
greatest increase in entropy?
(1) CaCO3(s) → CaO(s) + CO2(g)
(2) 2 Mg(s) + O2(g) → 2 MgO(s)
(3) H2O(g) → H2O(ℓ)
(4) CO2(g) → CO2(s)
22. Given the reaction system in a closed
container at equilibrium and at a temperature of
298 K:
N2O4(g)
2NO2(g)
The measurable quantities of the gases at
equilibrium must be
(1) decreasing
(3) equal
(2) increasing
(4) constant
23. Which statement correctly describes a
chemical reaction at equilibrium?
(1) The concentrations of the products and
reactants are equal.
(2) The concentrations of the products and
reactants are constant.
(3) The rate of the forward reaction is less than
the rate of the reverse reaction.
(4) The rate of the forward reaction is greater
than the rate of the reverse reaction.
24. Which type or types of change, if any, can
reach equilibrium?
(1) a chemical change, only
(2) a physical change, only
(3) both a chemical and a physical change
(4) neither a chemical nor a physical change
25. A student adds solid KCl to water in a
flask. The flask is sealed with a stopper and
thoroughly shaken until no more solid KCl
dissolves. Some solid KCl is still visible in the
flask. The solution in the flask is
(1) saturated and is at equilibrium with the
solid KCl
(2) saturated and is not at equilibrium with the
solid KCl
(3) unsaturated and is at equilibrium with the
solid KCl
(4) unsaturated and is not at equilibrium with
the solid KCl
26. Which statement must be true about a
chemical system at equilibrium?
(1) The forward and reverse reactions stop.
(2) The concentration of reactants and products
are equal.
(3) The rate of the forward reaction is equal to
the rate of the reverse reaction.
(4) The number of moles of reactants is equal
to the number of moles of product.
27. Given the reaction at equilibrium:
H2(g) + Br2(g)
2 HBr(g)
The rate of the forward reaction is
(1) greater than the rate of the reverse reaction
(2) less than the rate of the reverse reaction
(3) equal to the rate of the reverse reaction
(4) independent of the rate of the reverse
reaction
28. Which statement about a system at
equilibrium is true?
(1) The forward reaction rate is less than the
reverse reaction rate.
(2) The forward reaction rate is greater than the
reverse reaction rate.
(3) The forward reaction rate is equal to the
reverse reaction rate.
(4) The forward reaction rate stops and the
reverse reaction rate continues.
29. Given the equation: H2O(s)
H2O(ℓ)
At which temperature will equilibrium exist
when the atmospheric pressure is 1 atm?
(1) 0 K
(3) 273 K
(2) 100 K
(4) 373 K
30. A solution that is at equilibrium must be
(1) concentrated
(3) saturated
(2) dilute
(4) unsaturated
3
31. The solid and liquid phases of water can
exist in a state of equilibrium at 1 atmosphere
of pressure and a temperature of
(1) 0°C
(3) 273°C
(2) 100°C
(4) 373°C
32. A catalyst is added to a system at
equilibrium. If the temperature remains
constant, the activation energy of the forward
reaction
(1) decreases
(3) remains the same
(2) increases
33. Given the equilibrium reaction at STP:
N2O4(g)
2 NO2(g)
Which statement correctly describes this
system?
(1) The forward and reverse reaction rates are
equal.
(2) The forward and reverse reaction rates are
both increasing.
(3) The concentrations of N2O4(g) and NO2 are
equal.
(4) The concentrations of N2O4(g) and NO2 are
both increasing.
34. Given the reaction:
36. Given the reaction
N2(g) + O2(g) + 182.6 kJ
2 NO(g)
Which change would cause an immediate
increase in the rate of the forward reaction?
(1) increasing the concentration of NO(g)
(2) increasing the concentration of N2(g)
(3) decreasing the reaction temperature
(4) decreasing the reaction pressure
37. Given the system at equilibrium:
N2O4(g) + 58.1 kJ
2 NO2(g)
What will be the result of an increase in
temperature at constant pressure?
(1) The equilibrium will shift to the left, and
the concentration of NO2(g) will decrease.
(2) The equilibrium will shift to the left, and
the concentration of NO2(g) will increase.
(3) The equilibrium will shift to the right, and
the concentration of NO2(g) will decrease.
(4) The equilibrium will shift to the right, and
the concentration of NO2(g) will increase.
38. Given the reaction at equilibrium:
N2(g) + O2(g) + energy
2NO(g)
Which change will result in a decrease in the
amount of NO(g) formed?
(1) decreasing the pressure
(2) decreasing the concentration of N2(g)
(3) increasing the concentration of O2(g)
(4) increasing the temperature
39. Given the equilibrium reaction in a closed
system:
H2(g) + I2(g) + heat
2 HI(g)
What will be the result of an increase in
temperature?
(1) The equilibrium will shift to the left and
[H2] will increase.
(2) The equilibrium will shift to the left and
[H2] will decrease.
(3) The equilibrium will shift to the right and
[HI] will increase.
(4) The equilibrium will shift to the right and
[HI] will decrease.
AgCl(s)
Ag+(aq) + Cl-(aq)
Once equilibrium is reached, which statement
is accurate?
(1) The concentration of Ag+(aq) is greater than
the concentration of Cl–(aq).
(2) The AgCl(s) will be completely consumed.
(3) The rates of the forward and reverse
reactions are equal.
(4) The entropy of the forward reaction will
continue to decrease.
35. Given the reaction at equilibrium:
A(g) + B(g)
AB(g) + heat
The concentration of A(g) can be increased by
(1) lowering the temperature
(2) adding a catalyst
(3) increasing the concentration of AB(g)
(4) increasing the concentration of B(g)
4
Base your answers to questions 68 through 70 on the information and table below.
A student conducts an experiment to determine how the temperature of water affects the rate at
which an antacid tablet dissolves in the water. The student has three antacid tablets of the same size
and composition. The student drops one tablet into each of three beakers containing 200. milliliters of
water at different temperatures and measures the time it takes for each tablet to completely dissolve.
The results are shown in the table below.
Dissolving Data for Three Antacid Tablets
Beaker
Original
Time for Tablet 40. Describe the effect of water temperature on the rate
of dissolving. [1]
Temperature
to Dissolve
41. Explain, in terms of collision theory, how water
of Water (°C)
(s)
temperature influences the rate of dissolving. [1]
1
20.
40.
42. What change, other than temperature, would affect
2
30.
25
the rate of dissolving? [1]
3
40.
10.
Base your answers to questions 74 through 76 on the information below.
A student wishes to investigate how the reaction rate changes with a change in concentration of
HCl(aq).
Given the reaction: Zn(s) + HCl(aq) → H2(g) + ZnCl2(aq)
43. Identify the independent variable in this investigation. [1]
44. Identify one other variable that might affect the rate and should be held constant during this
investigation. [1]
45. Describe the effect of increasing the concentration of HCl(aq) on the reaction rate and justify your
response in terms of collision theory. [1]
Base your answers to question 23 on the potential energy diagram and the equation below.
46. The letter B represents which chemical formula or
formulas in the equation? [1]
47. If 682.2 kilojoules are absorbed, how many moles
of C2H2(g) are produced? [1]
48. Describe how the potential energy diagram will
change if a catalyst is added. [1]
2 C(s) + H2(g) + 227.4 kJ → C2H2(g)
Base your answers to questions 67 through 69 on the information below.
Given the equation for the dissolving of sodium chloride in water:
NaCl(s)
Na+(aq) + Cl–(aq)
49. Describe what happens to entropy during this dissolving process. [1]
50. Explain, in terms of particles, why NaCl(s) does not conduct electricity. [1]
51. When NaCl(s) is added to water in a 250-milliliter beaker, the temperature of the
mixture is lower than the original temperature of the water. Describe this observation in terms of heat
flow. [1]
88
Base your answers to questions 77 through 79 on the information and potential energy diagram below.
Chemical cold packs are often used to reduce swelling after an athletic injury. The diagram
represents the potential energy changes when a cold pack is activated.
52. Which lettered interval on the diagram represents
the potential energy of the products? [1]
53. Which lettered interval on the diagram represents
the heat of reaction? [1]
54. Identify a reactant listed in Reference Table I that
could be mixed with water for use in a chemical cold
pack. [1]
Base your answers to questions 53 through 55 on the potential energy diagram below.
55. What is the heat of reaction for
the forward reaction? [1]
56. What is the activation energy for
the forward reaction with the
catalyst? [1]
57. Explain, in terms of the function
of a catalyst, why the curves on the
potential energy diagram for the
catalyzed and uncatalyzed reactions
are different. [1]
58. On the set of axes provided below, sketch the potential energy diagram for an endothermic
chemical reaction that shows the activation energy and the potential energy of the reactants and the
potential energy of the products. [2]
89
Base your answers to questions 55 and 56 on the information and diagram below, which represent the
changes in potential energy that occur during the given reaction.
Given the reaction: A + B → C
59. Does the diagram illustrate an exothermic or an
endothermic reaction? State one reason, in terms of
energy, to support your answer. [2]
60. On the diagram provided at left, draw a dashed line to
indicate a potential energy curve for the reaction if a
catalyst is added. [1]
Base your answers to questions 79 and 80 on the information and equation below.
Human blood contains dissolved carbonic acid, H2CO3, in equilibrium with carbon dioxide and
water. The equilibrium system is shown below.
H2CO3(aq)
CO2(aq) + H2O(ℓ)
61. Explain, using LeChatelier’s principle, why decreasing the concentration of CO2 decreases the
concentration of H2CO3. [1]
62. What is the oxidation number of carbon in H2CO3(aq)? [1]
63. Explain how a catalyst may increase the rate of a chemical reaction. [1]
64. Given the reaction at equilibrium:
N2(g) + 3 H2(g)
2 NH3(g) + 92.05 kJ
a State the effect on the number of moles of N2(g) if the temperature of the system is increased. [1]
b State the effect on the number of moles of H2(g) if the pressure on the system is increased. [1]
c State the effect on the number of moles of NH3(g) if a catalyst is introduced into the reaction system.
Explain why this occurs. [2]
Base your answers to questions 59 and 60 on the information and balanced equation below.
Given the equation for a reaction at equilibrium:
2SO2(g) + O2(g)
2SO3(g) + energy
65. Explain, in terms of LeChatelier’s principle, why the concentration of SO2(g) increases when the
temperature is increased. [1]
66. Explain, in terms of collisions between molecules, why increasing the concentration of O2(g)
produces a decrease in the concentration of SO2(g). [1]
Base your answers to questions 63 and 64 on the information below.
Given the equilibrium equation at 298 K:
KNO3(s) + 34.89 kJ
K+(aq) + NO3–(aq)
67. Describe, in terms of LeChatelier’s principle, why an increase in temperature increases the
solubility of KNO3. [1]
68. The equation indicates that KNO3 has formed a saturated solution. Explain, in terms of
equilibrium, why the solution is saturated. [1]
90
Base your answers to questions 57 and 58 on the information below.
Given the reaction at equilibrium:
2NO2(g) + 7H2(g)
2NH3(g) + 4H2O(g) + 1127 kJ
69. On the diagram below, complete the potential energy diagram for the
forward reaction. Be sure your drawing shows the activation energy and the potential
energy of the products. [2]
70. Explain, in terms of Le Chatelier’s principle, why the concentration of NH3(g) decreases when the
temperature of the equilibrium system increases. [1]
91