Chapter 12 Review
Vocabulary
9.
Match each word to the sentence where it best
fits.
Section 12.1
A general description of any equilibrium reaction
can be explained by the _____________, which
shows the relationship of chemicals and their
molar coefficients.
10. We use the ________________ to determine
unknown equilibrium concentrations.
reaction rate
activation energy
transition state
activated complex
reaction profile
11. The value of the ___________________ only
changes when the temperature changes.
1.
The _____________ is the smallest amount of
energy necessary for molecules to react.
12. This special ratio called the
________________describes the relationship of
the products relative to the reactants in a chemical
equilibrium system.
2.
The speed or ____________ of a chemical
reaction is measured by the change in
concentration of a reactant or product, per unit
time.
Section 12.3
3.
4.
A graph that shows the progress of a chemical
reaction with respect to energy is called a
__________________.
Bonds are broken and reformed at this high
energy point called the _______________.
_____________ and _______________ refer to the same high energy peak on a reaction profile.
Section 12.2
closed system
equilibrium position
equilibrium
LeChatelier’s Principle
Law of Mass Action
equilibrium expression
equilibrium constant
reaction mechanism
intermediate
bimolecular
unimolecular
elementary steps
rate determining step
13. A reaction _____________ is a chemical species
formed during the elementary steps, and then
consumed, so it is not present in the overall
equation.
14. An elementary step that shows the collision of
two molecules is called a ____________ collision.
15. A series of ___________________ which
represent the overall progress of the chemical
reaction.
5.
The __________________ tells us which
direction of a reversible reaction is favored.
16. A proposed pathway or ______________ must
be supported by experimental evidence.
6.
During _________________ the rate of the
forward reaction is equal to the rate of the reverse
reaction.
17. The slow step in a reaction mechanism is called
the _________________.
7.
8.
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In the laboratory we sometimes observe a
_________________, where the chemicals are not
open to the environment.
___________________ states that when a change
is experienced by a chemical system in
equilibrium the system will adjust to partially
offset the change.
18. An elementary step that involves only one
reactant is called a ________________ collision.
Section 12.4
enzyme
catalyst
19. A substance that speeds up a chemical reaction is
called a _____________.
A NATURAL APPROACH TO CHEMISTRY
20. An _____________ is a biological catalyst the
speeds up chemical reactions in our bodies.
Conceptual Questions
Section 12.1
21.
32. Look at the graph below and label the following:
a. reactants, products
b. activated complex, Ac
c. the activation energy, Ea
d) the overall energy change, ΔH in the
reaction.
List the four factors affecting reaction rate.
22. Give an example of how decreasing the
temperature affects the rate of a chemical reaction.
23. Explain how a catalyst like rhodium, Rh, works in
a catalytic converter.
24. When strips of magnesium metal are added to a
beaker containing 1.0M HCl and another beaker
containing 6.0M HCl which one will have the
strongest reaction? Explain.
25. How do we measure the “speed” of a chemical
reaction?
26. During the course of a chemical reaction the rate
changes. Explain how it changes. In other words
does it speed up or slow down? and why does it do
this?
27. When we measure the “average” rate during a
chemical reaction, what formula do we use?
28. Refer to the hypothetical reaction below:
A + B → 2C
a. How does the rate of disappearance of
substance A relate to the rate of disappearance
of B? Explain.
b. How does the rate of appearance of substance
C relate to the disappearance of substance A?
Explain.
33. For a chemical reaction where A + B → C+D, the
overall energy change is endothermic. Make a
sketch of the reaction profile that represents the
endothermic reaction, given that the ΔH is 50 kJ.
34. Explain why endothermic reactions are less likely
to occur compared to exothermic reactions. To
answer this use the information related to a
reaction profile.
35. Explain what the graph below is telling us.
29. List the factors that are important during a
molecular collision.
30. If molecules collide will they react to form
product? Explain.
31. After the activated complex forms during a
chemical reaction, what happens next?
A NATURAL APPROACH TO CHEMISTRY
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Chapter 12 Review.
Section 12.2
36. Give an everyday example of equilibrium in your
daily life. Explain how this example works.
37. Explain how water inside a closed container
reaches an equilibrium balance between molecules
in the liquid and vapor phase.
38. Explain what we mean when we say “equilibrium
is a dynamic process.”
39. In order for equilibrium to be established in a
system, does there have to be equal amounts of
reactants and products? Why or why not?
40. Remarkably an equilibrium balance can be
established in a closed container, even when we
start with only the reactants! Explain to the best
of your ability, why this is true.
41. When we look at the graphs below, explain which
side (reactants or products) is favored in this
equilibrium system
2SO3(g) .
2SO2(g) + O2(g)
45. Given the reaction below, predict in which
direction the equilibrium will shift under with the
following changes.
PCl3(g) + Cl2(g) ΔH = 87.9 kJ
PCl5(g)
a. The pressure of the system is increased.
b. Some Cl2(g) is removed.
c. Some PCl5(g) is added.
d. The temperature of the system is decreased.
46. How will each of the following changes effect the
equilibrium system shown below?
2SO2(g) + O2(g)
2 SO3(g) ΔH = - 320 kJ
a. the temperature is increased
b. some O2(g) is removed
c. the pressure of the reaction mixture is
decreased
d. some SO3(g) is removed.
47. Write the expression for the equilibrium constants
for each of the following reactions.
a. N2(g) + O2(g)
2NO(g)
b. PCl5(g)
PCl3(g) + Cl2(g)
2 SO3(g)
c. 2SO2(g) + O2(g)
d. 2Cl2(g) + 2H2O(g)
4HCl(g) + O2(g)
e. 3NO(g)
N2O(g) + NO2(g)
Section 12.3
42. Chemists working in the lab need to know which
side of an equilibrium system is favored. Why
would this be important?
43. In your own words describe Le Chatelier’s
principle.
44. Consider the following equilibrium system:
2NO2(g) ΔH = 58.0 kJ
N2O4(g)
Predict the direction the equilibrium will shift
under the following conditions:
a. some N2O4(g) is removed
b. some NO2(g) is added
c. The temperature is increased.
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48. A reaction mechanism is a “series” of elementary
steps that make up an overall chemical reaction.
Does it make sense that chemical reactions
actually happen in a series of smaller steps?
Explain your thinking.
49. Given the two elementary steps below:
step 1: N2O(g) → N2(g) + O2(g)
step 2: N2O(g) + O → N2(g) + O2(g)
a. Write the balanced equation for the overall
chemical reaction.
b. Identify any reaction intermediates.
50. Given the elementary steps below:
step 1: H2(g) + ICl(g) → HI(g) + HCl(g)
step 2: HI(g) + ICl(g) → I2(g) + HCl(g)
A NATURAL APPROACH TO CHEMISTRY
a. Write the balanced equation for the overall
chemical reaction.
b. Identify any reaction intermediates.
51. Explain why it is unlikely that the following
reaction occurs all in one step!
2 SO3(g)
2SO2(g) + O2(g)
52. Give an example of one biological pathway in
your body. Explain why you consider it a
“pathway.”
Section 12.4
53. How does a catalyst speed up a chemical reaction?
54. Does our body use catalysts? If so what are they
called?
55. Make a generic sketch of a reaction profile, and
label your axis. Clearly show how a catalyst
would effect your graph.
56. Why will jello not set-up or “gel” when fresh
pinapple is added?
57. Give an example of an enzyme in your body that is
involved in the digestion process.
58. Explain one way that catalysts are useful in our
society.
59. How does the formation of stalagmites and
stalactites in caves relate to our study of
equilibrium?
Quantitative Problems
Section 12.1
60. The reaction of nitrogen and oxygen to produce
nitrous oxide is shown below:
2NO(g)
N2(g) + O2(g)
The rate of disappearance of N2(g) is measured to
be 4.3 x 10 -5 M/s. What is the rate of formation
of NO(g)?
61. The decomposition of NO is shown below.
3NO(g)
N2O(g) + NO2(g)
What is the rate of disappearance of NO if the rate
A NATURAL APPROACH TO CHEMISTRY
of appearance of N2O(g) was measured to be 3.6 x
10 -4 M/s.
62. Use the data in the table below to answer the
following questions about the reaction where
A→ C
Time (min)
0
5
10
15
20
Moles A
1.00
0.85
0.74
0.62
0.54
Moles C
0.00
0.15
0.26
0.38
0.46
a. What do you notice about the amounts of
reactant relative to the product being formed?
b. Calculate the average rate for the appearance
of C during the time period of t = 5min to t =
10 min.
c. Calculate the rate of disappearance of A
during the first five minutes of the reaction
d. Calculate the rate of disappearance of A
during the last five minutes, where t = 15 min
and t = 20 min.
e. What do you notice about the rate at the start
of the reaction relative to the rate at the end of
the reaction.
Section 12.2
63. For the following reactions look at the value of the
equilibrium constant to decide whether the
reaction contains mainly reactants or mainly
products.
2NO2(g), K = 5.0 x1012
a. 2NO(g) + O2(g)
b. 2SO3(g)
2SO2(g) + O2(g) K= 4.0 x 10-10
Explain your reasoning.
64. Carbon monoxide and hydrogen gas are catalyzed
to commercially produce methanol.
CH3OH(g)
CO(g) + 2H2(g)
Calculate the value of K at a constant temperature
of 227oC. Given that there are 0.041 moles of
CH3OH, 0.17 mole CO, and 0.30 moles H2
present in a 2.0 L reaction vessel.
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