Lecture 2, MWF 11:15 Day
Answers to the multiple-choice questions
are given after the questions.
The
multiple-choice portion of this exam has 21 questions on 5 pages totaling 85 points.
Be sure to include your name and 9 digit ID number on the answer sheet. Lecture
section 2 goes in column K. Blacken in all selections using a No. 2 pencil.
The
written portion of this exam has 2 questions totaling 15 points and is to be
done on the question sheet in the spaces provided. Be sure to fill in your name
and 9 digit ID number.
Turn in both the bubble
answer sheet and the hand written sheet. Keep the multiple-choice questions to check your
answers against the posted key.
Answers
to the questions will be posted on the web as soon as possible after the exam.
Information
for your use:
K = °C + 273 R
= 0.08206 Latm/mol·K = 8.314 J/mol·K
[A] = [A]o - kt
ln[A] = ln[A]o - kt ln{[A]/[A]o} =
-kt kt½ = ln2 = 0.693
1/[A] = 1/[A]o + kt
k = Ae-Ea/RT ln k = ln A - (Ea/R)(1/T) ln(k2/k1)
= -(Ea/R)(1/T2 – 1/T1)
Kp = Kc(RT) D n
pH = - log [H3O+] pOH = - log [OH-]
At 25 °C, Kw = [H3O+]
[OH-] = 1.0 x 10-14 pH
+ pOH = 14
1.
(3
points) In general, the rates of chemical reactions increase with temperature
because at higher temperature
(A) the
concentrations of the reactants are higher
(B)
exothermic reactions are favored
(C) the
fraction of molecules with enough energy to react is higher
(D) the
activation energy for the reaction is lower
(E) DH for the reaction is lower
2.
(6 points) For the gas phase reaction 2 NO + 2 H2 ® N2 + 2 H2O , the following initial
rates of disappearance of NO were obtained: From these data, the rate law for
the reaction is:
|
[NO]o, M |
[H2]o,
M |
Initial Rate, Ms-1 |
|
0.380 |
0.480 |
0.100 |
|
0.190 |
0.960 |
0.050 |
|
0.380 |
0.960 |
0.200 |
(A)
Rate
= k[NO] [H2] (C) Rate = k[NO] [H2]2 (E)
Rate = k[H2]2
(B)
Rate
= k[NO]2 [H2] (D) Rate = k[NO]2
3.
(4 points) The rate constant for the second order decomposition of H2O2
in the gas phase at 400 °C is 0.65 M-1s-1.
If the initial concentration of H2O2 is 0.10 M, how many
seconds are required for the concentration to drop to 0.050 M?
(A) 0.077 (B) 1.1 (C) 15 (D) 31 (E) 42
4.
(4 points) For the decomposition of hydrogen
iodide on a gold surface at 150 °C, 2HI ® H2 + I2, it is observed that a plot of [HI]
versus time in seconds gives a straight line with a slope of -1.7 x 10-4 Ms-1. The
rate law for this reaction is:
(A) Rate =
1.7 x 10-4 (C) Rate = 1.7 x 10-4[HI]2
(E) Rate = 5.9 x 103[HI]2
(B) Rate =
1.7 x 10-4[HI] (D) Rate = 5.9 x 103[HI]
5.
(4
points) The following data are for the first order decomposition of nitramide
in aqueous solution, NH2NO2(aq) ® N2O(aq) + H2O(l), at 25 °C. What is the rate constant
for the reaction at 25 °C in min-1?
|
[NH2NO2],
M |
0.44 |
0.33 |
0.22 |
0.11 |
|
time, min |
0 |
71 |
170 |
340 |
(A) 1.4 x 10-2 (B) 9.8 x 10-3 (C) 5.9 x 10-3 (D) 4.1 x 10-3 (E) 7.1 x 10-4
6.
(4
points) The rate constant for the gas phase decomposition of bromoethane, C2H5Br ® C2H4 + HBr, has been determined at several
temperatures. When ln k is plotted against the reciprocal of the Kelvin
temperature, the resulting linear plot has a slope of -2.63 x 104 and a y-intercept of
29.6. What is the activation energy in kJ for this reaction?
(A) 10.2 (B) 29.6 (C)
219 (D) 246 (E)
316
Questions 7 - 9 are
based on the following two-step mechanism proposed for the decomposition of
acetaldehyde in the presence of iodine.
CH3CHO + I2 ® CH3I + CO + HI slow
CH3I + HI ® CH4 + I2 fast
7.
(3 points) The overall reaction is
(A) CH3CHO
+ I2 ® CH3I
+ CO + HI (D) CH4 + CO ® CH3CHO
(B) CH3I
+ HI ® CH4 + I2 (E) CH3CHO ® CH4 + CO
(C) CH3CHO
+ I2 ® CH4 + I2 + CO
8.
(3
points) The catalyst is:
(A) I2 (B)
CH3I (C)
CO (D) HI (E) there is none
9.
(4
points) The rate law consistent with this mechanism is:
(A) Rate = k[CH3CHO] (C) Rate = k[CH3I][I2]
(E) Rate = k[CH3CHO][I2]
(B) Rate = k[CH3CHO]2 (D) Rate = k[CH3I][
HI]
10.
(5 points) Solid ammonium iodide decomposes at 400 °C to form ammonia and hydrogen iodide as
gases: NH4I(s) « NH3(g)
+ HI(g). When 0.0200 mol of NH4I(s) is placed into an evacuated 1.00
L container at 400 °C, at equilibrium the
concentrations of both NH3 and HI are found to be 0.0084 M. What is
the value of Kc for this reaction at 400 °C?
(A) 8.4 x 10-1
(B) 1.7 x 10-2 (C) 6.1 x 10-3 (D)
3.5 x 10-3 (E) 7.1 x 10-5
Questions
11and 12 refer to the following reaction:
COCl2(g)
« CO(g) + Cl2(g) for which KC = 0.320 at 727 °C
11.
(4
points) When 0.050 mol of each of the three gases is introduced into an
evacuated 1.0 liter container at 727 °C,
(A)
a reaction will take place in which COCl2
is produced and CO is consumed.
(B)
a reaction will take place in which COCl2
is consumed and CO is produced.
(C)
a reaction will take place in which CO is
produced and Cl2 is consumed.
(D)
a reaction will take place in which CO is
consumed and Cl2 is produced.
(E)
No reaction will occur
12.
(4
points) What is the value of KP for this equilibrium reaction at 727
°C?.
(A) 0.00400 (B)
19.1 (C)
26.3 (D)
320 (E) 1930
Questions 13 through 16 are
based on the following gas phase equilibrium and related data:
2 NOBr(g) « 2
NO(g) + Br2(g) DH = 16.1 kJ and KC
= 0.0064 at 25°C.
13.
(4 points) If the volume of the above
equilibrium system is decreased at constant temperature, the amount of NO(g)
will ______ and the value of KC will _______ .
(A) increase, decrease (C) decrease, increase (E) increase, not change
(B) increase, increase (D) decrease, not change
14.
(4
points) If additional NO(g) is added to the above equilibrium system at
constant volume and temperature, the amount of NOBr will ______ and the value
of the equilibrium constant will _______ .
(A) increase, decrease (C) decrease, increase (E) increase, not change
(B) decrease, decrease (D) decrease, not change
15.
(4
points) If the temperature of the above equilibrium system were raised to 100°C, the value of the equilibrium constant
would
(A) increase (C)
not change (E)
decrease then increase
(B) decrease (D)
increase then decrease
16.
(4 points) What is the value of KC
at 25 °C for the reaction
NOBr(g) « NO(g) + ½ Br2 (g)
(A) 4.1 x 10-5 (B) 3.2 x 10-3 (C) 1.3 x 10-2 (D) 8.0 x 10-2 (E) 1.6 x 102
Questions 17 - 19 refer to
the following equilibrium taking place in aqueous solution:
HCN + H2O « H3O+
+ CN – KC = 4.9 x 10-10
17.
(4
points) When 0.10 mol of HCN is dissolved in 1 L of water, at equilibrium:
(A)
the
system will be predominantly H3O+ and CN –
(B)
the
system will be predominantly HCN and H2O
(C)
equal
amounts of H2O and H3O+ will be present
(D)
equal
amounts of HCN and CN – will be present
(E)
0.10
mol of CN – will be present
18.
(4
points) The strongest Bronsted-Lowry
base in the equilibrium system is:
(A) HCN (B) CN – (C)
H3O+ (D)
H2O (E) there is none
19.
(4
points) The conjugate ______ of H2O is ______ .
(A) acid, CN
– (C) acid, H3O+ (E) acid, HCN
(B) base, CN
– (D)
base, H3O+
20.
(4
points) Which one of the following aqueous solutions is acidic?
(A) pOH =
9.0 (C) pH = 8.0 (E)
none is acidic
(B) [OH-] = 1.0 x 10-5 (D) [H3O+] = 2.0 x 10-8
21.
(5
points) A concentrated aqueous ammonia solution has a pH of 12.17. What is the
[H3O+] in this solution ?
(A) 3.2 x 10-12 (B)
6.8 x 10-13 (C) 2.6 x 10-3 (D)
1.5 x 10-2 (E)
1.1 x 10-1
The following list gives the number of points for each answer, in the order ABCDE, for each question. The correct answer to each question is the one worth the most points.
1
00300
2
36030
3
00400
4
41100
5
00040
6
00400
7
00003
8
30000
9
00024
10
00305
11
04000
12
03400
13
00242
14
20024
15
40000
16
00040
17
04000
18
04020
19
00400
20
40000
21
05000