PRACTICE EXAM 2-C
CHEMISTRY E-1ax
Problems from this exam will be discussed in sections
prior to the exam.
LAST NAME: ________________________________________
FIRST NAME: ________________________________________
You should give yourself 2 hours to complete this exam
NOTES:
1. This exam has 6 pages with 6 problems, plus the cover sheet, useful information,
periodic table, and scrap paper.
2. Note the point values of each exam question, and consider where you can best spend
your time.
3. Answer all questions on the exam sheets. Put your final answers in the boxes
provided. If you must use the back, then please indicate that clearly!
4. Do not use red pen!
5. For full credit, show all calculations; this also helps us award partial credit.
6. All numerical answers must include correct units for full credit.
1. ____________
2. ____________
3. ____________
4. ____________
5. ____________
6. ____________
TOTAL: ___________ / 100
1
1.
Answer the questions below. Parts (a), (b), and (c) are all separate, independent questions.
a)
A 1.00-liter vessel is filled with 0.200 moles of oxygen gas at 25°C. Determine the
pressure inside the vessel. (4 pts)
P=
b)
A rigid vessel is filled with 2.00 atmospheres of nitrogen gas and 5.00 atmospheres of
helium gas. Determine the total pressure in this vessel and determine the mole fraction of
nitrogen gas in this mixture. (4 pts)
XN2 (g) =
Ptotal =
c)
A steel reaction vessel at 50°C is filled with 1.20 atm of N2O4 gas. At this temperature,
some of the N2O4 will react according to the following balanced reaction:
N2O4 (g)
! 2 NO2 (g)
After some of the N2O4 has reacted, the total pressure in the vessel at 50°C is measured to
be 1.58 atm. Determine the partial pressure of N2O4 in the final gas mixture. (8 pts)
P (N2O4) =
1
( ______ / 16 pts)
2
2.
a)
Given the following data:
P4 (s) + 6 Cl2 (g) ! 4 PCl3 (g)
∆H° = –1150 kJ/mol
PCl5 (g) ! PCl3 (g) + Cl2 (g)
∆H° =
120 kJ/mol
Determine the change in enthalpy (∆H°) for the following reaction:
P4 (s) + 10 Cl2 (g) ! 4 PCl5 (g)
∆H° = ???
(6 pts)
∆H° =
b)
Use any data from the Useful Information page to determine ∆H° for the following reaction:
4 NH3 (g) + 5 O2 (g) ! 4 NO (g) + 6 H2O (g)
∆H° = ???
(6 pts)
∆H° =
c)
Consider the following balanced neutralization reaction between citric acid, which we
can abbreviate as H3Cit, and sodium hydroxide, NaOH:
H3Cit (aq) + 3 NaOH (aq) ! Na3Cit (aq) + 3 H2O (l)
∆H° = –173 kJ/mol
Using the above information, determine the total quantity of heat released when 1.00
moles of citric acid is mixed with 0.200 moles of sodium hydroxide and the above
reaction proceeds to completion. (4 pts)
heat released =
d)
A reaction is performed in a coffee-cup calorimeter and the temperature of the solution
decreases. From this information you can conclude that the reaction is: (circle) (2 pts)
endothermic
2
exothermic
( ______ / 18 pts)
3
3.
After working through several versions of the “iced-tea problem”, you decide to attempt a
similar experiment with a different substance. You choose stearic acid, a fatty acid that is
used in the production of chocolate, candy, candles, plastics, and cosmetics. Some data
for stearic acid is given below.
Data for stearic acid:
Molar mass = 284.5 g/mol
Melting point = 70°C
Specific heat of solid = 1.76 J/g°C
Specific heat of liquid = 2.30 J/g°C
Enthalpy of melting:
stearic acid (s) ! stearic acid (l) !H° = 56.6 kJ/mol
You mix together:
100. grams of solid stearic acid at 50°C
250. grams of liquid stearic acid at 100°C
After the stearic acid has thoroughly mixed, the entire mixture has a temperature of 70°C.
Some of the solid has melted, but some solid stearic acid remains. Determine the mass of
solid stearic acid that remains in the mixture. (16 pts)
mass of solid =
3
( ______ / 16 pts)
4
4.
An excited-state hydrogen atom has its electron in the 4px orbital. This electron
undergoes a transition to the ground state, resulting in the emission of a photon of light.
This photon then strikes the surface of a piece of silver metal, causing an electron to be
ejected from the surface of the silver via the photoelectric effect. Determine the
maximum kinetic energy of this emitted electron. (The photoelectric binding energy of
silver is 456 kJ/mol.) (16 pts)
KEelectron =
4
( ______ / 16 pts)
5
5.
a)
Identify the n and l quantum numbers and all possible ml and ms quantum numbers for an
electron in a 6p orbital. (4 pts)
n=
l=
all possible ml:
b)
all possible ms:
For parts (i) and (ii) below, identify a type of orbital (for example: “2p”) that has the
indicated number of angular or radial nodes. For each one, there could be several correct
answers. Please write only one answer in each box. (2 pts)
i) Has exactly 3 angular nodes:
ii) Has exactly 3 radial nodes:
c)
In the box below, list the names of the five different orbitals in the 4d subshell.
(For example, the three different orbitals in the 2p subshell are: 2px, 2py, and 2pz. We
are looking for a similar list of the orbitals in the 4d subshell.) (2 pts)
d)
In the space below, draw a sketch of a 4px orbital that clearly shows the shape and
orientation of the orbital and indicates the location of all nodes. Label nodes as “angular”
or “radial”, and be sure to label any axes that you draw. (4 pts)
e)
For each of the following atoms, write the ground-state electron configurations using
noble-gas abbreviations, and indicate the number of unpaired electrons in each atom.
(The atomic number of each element is also indicated.) (6 pts)
e– configuration
# unpaired e–
Mn (Z = 25):
Pb (Z = 82):
Cm (Z = 96):
5
( ______ / 18 pts)
6
6.
A reaction vessel is fitted with a movable piston that allows the volume of the vessel to
expand and contract and maintains a constant external pressure of 1.00 atm. The vessel is
filled with nitrogen gas and a small amount of liquid water at a temperature of 50°C. The
volume of gas contained in the vessel at 50°C and 1.00 atm total pressure is 1.00 liters.
a)
The temperature of the vessel is increased to 80°C, and the volume of the gas expands
against the movable piston. At 80°C and 1.00 atm total pressure, there is still a small
amount of liquid water present in the vessel. Determine w, work, for this system in units
of Joules. (10 pts)
w=
b)
What can you conclude about the sign of q for the gas/water mixture as the temperature of
the system is increased from 50°C to 80°C? (2 pts)
(circle)
c)
q=0
q>0
water vapor
neither, they are the same
Which gas has the greater average kinetic energy per mole at 80°C? (circle) (2 pts)
nitrogen gas
6
q<0
Which gas has the greater root mean square speed (uRMS) at 80°C? (circle) (2 pts)
nitrogen gas
d)
Joules
water vapor
neither, they are the same
( ______ / 16 pts)
Scrap Paper
Nothing on this page will be graded unless you clearly indicate
on a specific problem that additional work is located here.
Useful Information
This page will NOT be collected after the exam.
We will NOT grade anything written on this page.
Avogadro’s Number = 6.02 ! 1023
R = 0.0821 L·atm/mol·K = 8.31 J/mol·K
kg·m2
1 Joule (J) = 1 s2
Boltzmann’s constant = 1.381 ! 10–23 J/K
Planck’s Constant h = 6.63 ! 10–34 J·s
Speed of light = 3.00 ! 108 m/s
Mass of electron = 9.11 ! 10–31 kg
Rydberg Constant RH = 2.18 ! 10–18 J
1 Å = 10–10 m
1 atm = 760 torr = 760 mmHg
1 mL = 1 cm3
1 L·atm = 101.3 J
Properties of Water
Freezing Point = 0.°C = 273. K
Boiling Point = 100.°C = 373. K
Vapor Pressure at 25°C = 23.8 torr
Vapor Pressure at 50°C = 92.5 torr
Vapor Pressure at 80°C = 355.1 torr
Standard Enthalpies of Formation at 25°C
Substance
!H°f
NH3 (g)
–46.3 kJ/mol
NO (g)
H2O (g)
90.4 kJ/mol
–241.8 kJ/mol
27
Co
28
Ni
29
Cu
30
Zn
Fr
Cs
227.03
Ac
138.91
89
La
Y
88.91
57
(261)
Rf
178.49
104
Hf
Zr
91.22
72
47.88
40
Actinide series
Lanthanide series
Ra
Ba
Sr
44.96
39
231.04
Pa
232.04
Th
140.91
91
140.12
90
59
Pr
58
Ce
(263)
183.85
[106]
W
Mo
95.94
74
52.00
42
(262)
Ha
180.95
105
Ta
Nb
92.91
73
50.94
41
238.03
U
144.24
92
60
Nd
(262)
186.21
[107]
Re
Tc
(98)
75
54.94
43
237.05
Np
(145)
93
61
Pm
(265)
190.20
[108]
Os
Ru
101.07
76
55.85
44
(244)
Pu
150.36
94
62
Sm
(266)
192.22
[109]
Ir
Rh
102.91
77
58.93
45
(243)
Am
151.96
95
63
Eu
195.08
Pt
Pd
106.42
78
58.69
46
(247)
Cm
157.25
96
64
Gd
196.97
Au
Ag
107.87
79
63.55
47
(247)
Bk
158.93
97
65
Tb
200.59
Hg
Cd
112.41
80
65.39
48
(251)
Cf
162.50
98
66
Dy
204.38
Tl
In
114.82
81
69.72
49
Ga
(252)
Es
164.93
99
67
Ho
207.20
Pb
Sn
118.71
82
72.61
50
Ge
(257)
Fm
167.26
100
68
Er
208.98
Bi
Sb
121.76
83
74.92
51
As
(258)
Md
168.93
101
69
Tm
(209)
Po
Te
127.60
84
78.96
52
Se
(259)
No
173.04
102
70
Yb
(210)
At
I
126.91
85
79.90
53
Br
35.45
35
Cl
226.03
26
Fe
S
32.07
34
19.00
17
(223)
25
Mn
P
30.97
33
16.00
16
137.33
88
24
Cr
Si
28.09
32
14.01
15
132.91
87
V
23
Al
26.98
31
12.01
14
87.62
56
Rb
Ca
Mg
10.81
13
(260)
Lr
174.97
103
71
Lu
(222)
Rn
Xe
131.29
86
83.80
54
Kr
Ar
39.95
36
20.18
18
Ne
85.47
55
Ti
22
F
40.08
38
21
Sc
O
39.10
37
K
Na
Li
24.31
20
N
9
22.99
19
C
8
9.012
12
B
7
6.941
11
Be
6
4.003
10
5
4
1.008
3
2
He
H
1
PERIODIC TABLE OF THE ELEMENTS