Chem 12 Practice
Test 1 Answers
1. Consider
the following reaction mechanism:
step 1: M + X → MX
step 2: MX + A → D + X
The
chemical species MX is a(n)
A. catalyst
B. inhibitor
C. final
product
D. reaction intermediate
2. Consider
the following reaction: 2N2O5(g) → 4NO2(g) + O2(g)
At a
certain temperature the rate of decomposition of 2N2O5(g)
is 2.5 x 10-6 mol/s. The rate of formation
of NO2 is
A. 1.0 x 10-5 mol/s
B. 1.3 x 10-6 mol/s
C. 2.5 x 10-6 mol/s
D. 5.0 x 10-6 mol/s
3. Which of
the following factors affect the rates of both homogeneous and heterogeneous reactions.
I nature of the reactants
II presence of a catalyst
III temperature of system
IV concentration of reactants
A. I
and IV only
B. II
and III only
C. II,
III, and IV only
D. I, II, III, and IV
4. Which of
the following equations represents an endothermic reaction?
A. N2O4(g) +
59 kJ → 2NO2(g)
B. 2H2(g) + O2(g) → 2H2O(l) +
572 kJ
C. 2BrCl(g) -29.3 kJ
→Br2(g) + Cl2(g)
D. 2H2(g) + O2(g) → 2H2O(l) ΔH =
-572 kJ
5. Consider the potential energy diagram. The
activation energy for the reverse reaction is
A. 30
kJ
B. 140 kJ
C. 170
kJ
D. 200
kJ
6. Consider
the following mechanism: Step
1: Cl +
O3 → ClO +
O2
Step
2: O + ClO → Cl +
O2
The
reaction intermediate is
A. Cl
B. O2
C. O3
D. ClO
7. In a
reaction mechanism, the rate determining step is the
A. fastest
and has the lowest activation energy.
B. fastest
and has the highest activation energy.
C. slowest
and has the lowest activation energy.
D. slowest and has the highest activation energy.
8. A
catalyst increases the rate of a reaction by
A. increasing the concentration of
reactant(s).
B. decreasing the concentration of the
reactant(s).
C. increasing the activation energy of the
overall reaction.
D. decreasing the
activation energy of the overall reaction.
9. Which of
the following properties could be used to measure the rate of the following
reaction in a open container. Zn(s)
+ 2HCl(aq)
→ ZnCl2(aq) + H2(g)
A. mass of Zn
B. solubility
of HCl
C. concentration
of Cl-
D. colour of the solution
10.
Consider the following potential energy diagram:
The above
diagram represents an
A. exothermic reaction involving one step.
B. exothermic
reaction involving two steps.
C. endothermic reaction involving one step.
D. endothermic reaction involving two steps.
11. Which
of the following are necessary for successful collisions to occur?
I. Favourable
geometry
II. Sufficient energy
III. Large ΔH
A. I
only
B. I and II only
C. II
and III only
D. I,
II, and III
12.
Consider the following reaction: 2H2O2(aq) → 2H2O(l) +
O2(g)
When 1.0 g
of KI is added to the H2O2, bubbles of O2 are
produced at an increased rate, The KI is a
A. product
B. catalyst
C. reactant
D. intermediate
13.
Consider the following
I. Frequency of successful collision
II. Volume of the reaction vessel
III. Pressure of the system
IV Mass of the system
To increase
the rate of a chemical reaction there must be an increase in
A. I only
B. I
and III only
C. I,
III and IV only
D. I,
II, III, and IV
14.
Consider the following reaction mechanism:
Step1: ICl
+ H2 → HI
+ HCl slow
Step 2:
ICl +
HI → HCl
+ I2 fast
The species
HCl is a
A. product
B. catalyst
C. reactant
D. reaction
intermediate
15.Consider the following potential energy diagram:
75
50
50
25
25
The activation
energy in the forward direction is
A. 25
kJ
B. 50
kJ
C. 100 kJ
D. 125
kJ
16.
Consider the following reactions:
I. N2 + O2(g)
→ 2NO(g)
II. Mg(s) + O2(g)
→ 2MgO(s)
III. CaCO3(s) + 2H+(aq) → Ca2+ (aq) + H2O(l) + CO2(g)
Increasing
the surface area will increase the reaction rate in
A. II
only
B. I
and III only
C. II and III only
D. I,
II, and III
17.
Consider the following reaction mechanism: Step 1: V3+ + Cu2+ → V4+
+ Cu+ slow
Step 2: Cu+ + Fe3+→ Cu2+ + Fe2+ slow
The
reaction intermediate is
A. Cu+
B. Cu2+
C. V3+
D. Fe3+
18. The
rate of a chemical reaction can be expressed in
A. grams
per mole
B. energy
consumed per mole
C. volume of gas per unit time
D. mole
formed per litre of solution
19.
Consider the following reaction:
2MnO4-(aq) + 5C2O42-(aq) 16H+(aq) → 2Mn2+(aq) +
10CO2(g) + 8H2O(l)
The rate of
decomposition of the oxalate ion is increased by
A. adding NaOH.
B. removing
CO2
C. adding a catalyst
D. decreasing
the pressure
20. The
minimum amount of energy needed to start a reaction is called the
A. activation
energy.
B. energy of reaction.
C. entropy of reaction
D. reaction
mechanism energy
21. An
8.00g piece of magnesium was placed into 6.0 M HCl.
After 25 s, 3.50 g of unreacted magnesium remained.
The average rate at which magnesium was consumed is
A. 0.14
g/s
B. 0.18 g/s
C. 0.32
g/s
D. 4.50
g/s
22. In
general rates double when the temperature is increased by 10 oC. The temperature of a reaction is increased
by 40 oC. The rate will increase by a
factor of
A. 2
B. 4
C. 8
D. 16
23.
Consider the following factors
I. reactant particles collide
II. sufficient
kinetic energy is present
III. a favourable geometry exists
IV. catalysts are
present
Which
combination of the above factors is required for all successful collisions?
A. I
only
B. II
and III only
C. I, II and III only
D. I,
II, III, and IV
24.
Consider the following reaction at constant temperature in an open system:
MgCO3(s) + 2HCl(aq)
→ CO2(g) + H2O(l) + MgCl2(aq)
Which of the following properties could be used to determine the
reaction rate.
A. mass of the system
B. pressure
of the gas
C. concentration
of H2O
D. concentration
of MgCO3
25. Which combination of factors will affect the
rate of the following reaction?
MgCO3(s) + 2HCl(aq)
→ CO2(g) + H2O(l) + MgCl2(aq)
A. temperature
and surface area only
B. temperature
and concentration only
C. concentration
and surface area only
D. temperature, concentration, and surface
area only
26. As
reactant molecules approach each other
A. heat
is released
B. a
reaction intermediate forms
C. kinetic energy changes into potential
energy
D. potential
energy changes into kinetic energy
Consider
the following potential energy diagram for the next three five questions.
27. The
interval representing Ea catalyzed is
A. 1
B. 2
C. 3
D. 5
28. The
interval representing ΔH for the forward reaction is
A. 1
B. 2
C. 3
D. 4
29. The
interval representing Ea for the reverse reaction is
A. 1
B. 2
C. 3
D. 4
30. The
interval representing Ea for the forward reaction is
A. 1
B. 2
C. 3
D. 4
31. The
interval representing the energy of the activated complex is
A. 1
B. 2
C. 3
D. 4
32. When a
catalyst is added to a reaction, ΔH will
A. increase
slowly
B. remain constant
C. decrease
slowly
D. increase
rapidly due to the alternate pathway
33.
Consider the following reaction: Zn(s) + 2HCl(aq) →
H2(g) + ZnCl2(aq)
Data for
the reaction is shown below:
Time Mass of Zn (g) Volume of H2
(mL) Temperature
(oC)
0 4.65 0 20
2 4.50 50 21
4 4.35 100 22
The rate of
the reaction can be measured in units of
A. g/min
B. g/mL
C. min/mL
D. g/(mL)(oC)
34. When a
lit match is touched to the wick of a candle, the candle begins to burn. When
the match is removed, the candle continues to burn, the match,
A. behaves
as a catalyst
B. supplies the activation energy
C. is
part of the rate determining step
D. lowers
the activation energy barrier
35. Consider the following reaction: 2NO(g) + O2(g)
→ 2NO2(g)
+ 112 kJ
ΔH for
the above reaction is:
A. positive
and the reaction is exothermic
B. negative and the reaction is exothermic
C. positive
and the reaction is endothermic
D. negative
and the reaction is endothermic
36.
Consider the following reaction: 2S(s) + 3O2(g)
→ 2SO2(g) + heat
The rate of
this reaction could be increased by
A. decreasing
the temperature
B. adding a catalyst
C. increasing
the concentration of S
D. decreasing
the surface area of the S
37.
Consider the following reaction: ½H2 +
½I2 → HI
ΔH = +28 kJ
The
activation energy for the formation of HI is 167 kJ. The activation energy for
the decomposition of HI is
A.
28 kJ
B.
139 kJ
C. 167 kJ
D. 195 kJ
38. Some
reactants are more reactive than others because of their activation energy Ea.
What graph shows the relationship between Ea and rate.
39. The
activated complex is a chemical species that is
`
A. stable
and has low PE.
B. stable
and has high PE.
C. unstable
and has low PE.
D. unstable and has high PE.
40. As an activated
complex changes into products,
A. potential energy changes into kinetic
energy.
B. kinetic
energy changes into potential energy.
C. kinetic
energy changes into activation energy.
D. potential
energy changes into activation energy.
Chemistry
12 1999 Subjective
1. On the potential energy diagram above,
clearly label the activation energy, heat of the reaction (∆H), and the
energy of the activated complex. (3
marks)
2. Is the
above reaction endothermic or
exothermic in the forward direction? (1 mark)
3. On the
graph below, draw the potential energy diagram for an exothermic reaction and
label the activation energy. (2
marks)
4. Nitric
oxide (NO) is involved in the decomposition of ozone by the following
mechanism:
Step 1: O3 + sunlight → O2
+ O
Step 2: O3 +
NO → NO2 + O2
Step 3: NO2 +
O → NO
+ O2
a) Write
the net equation for the decomposition reaction
2O3 + sunlight →
3O2
b) Identify
a catalyst
NO
c) Identify
a reaction intermediate
NO2 and O
d) What is
the function of sunlight in this reaction? (4
marks)
Provides the activation energy
5. Consider
the following reaction: 2NO + 2H2 →
2H2O + N2
a) Explain
why the reaction is likely to involve more than one step.
Reactions that have more than three reactant particles likely have
mechanisms.
b) A
proposed mechanism for the above reaction is: Step 1: NO +
H2 → N
+ H2O
Step
2: ?
Step 3: N2O +
H2 → N2 + H2O
Write the
equation for step 2.
NO + N →
N2O
6. Define
the term activation energy.
The
minimum energy required for a successful collision
7. The
combustion of coal, C, produces carbon dioxide and water according to the
following equation: C(s) + O2(g)
→ CO2(g) +
394 kJ
a) What is ∆H
for this reaction? (1 mark)
∆H = -394 kJ
b) Using
the collision theory, explain why a lump of coal does not react with oxygen at
room temperature and pressure. (1 mark)
The Ea is too high for the room temperature collisions to be successful.
c) Many
coalmine disasters have resulted when a spark ignites coal dust in the air.
Explain using the collision theory. (2 marks)
The spark provides the Ea, the reaction is exothermic and has a high
surface area and an explosion results.
8. State
two reasons why some collisions may not result in a chemical reaction.
(2
marks)
Not sufficient energy
Poor collision geometry
9. A
student wishes to monitor the rate of the following reaction:
CaCO3(s) +
2HCl(aq) →
CaCl2(aq)
+ CO2(g) +
H2O(l)
Identify
two different properties that could be used to monitor the rate of the
reaction. Describe and explain the changes that would occur. Any two of the following.
Property 1 Mass of CaCO3
Change and
explanation Decreases as reactants are converted into products
Property 2 Concentration of HCl
Change and
explanation Decreases as reactants are converted into products
Property 3 Concentration of CaCl2
Change and explanation Increases
as reactants are converted into products
Property 4 Volume of CO2 gas
Change and
explanation Increases as reactants are converted into products
Property 5 Mass of open system
Change and
explanation Decreases as gas escapes
Property 6 Pressure of a closed system
Change and
explanation Increases as gas is produced
10. An experiment is done to determine the
rate of the following reaction:
2Al(s) + 6HCl(aq) →
3H2(g) + 2AlCl3(aq)
1.00 g of Al is placed in a beaker
and allowed
to react for 12.00 minutes
with 2.00 M
HCl. If the rate of consumption
of HCl is 0.250 g/min,
calculate the amount
of Al remaining.
12.00 min x 0.250 g HCl x 1
mol x 2 mol Al x 27.0 g = 0.740 g
1 min 36.5 g 6 mol HCl
1 mole
1.00 g
- 0.740 g
= 0.26
g Note
the loss of one sig fig.