Download Exam 3 Answer Key

CHEMISTRY 110
1.
S(s) + O2(g) → SO2(g)
S(s) + 2 O(g) → SO2(g)
S2+(s) + 2 O2-(g) → SO2(g)
S(s) + ½ O2(g) → SO(g)
2 S(s) + ½ O2(g) → S2O(g)
None of the above are correct.
Using the heats of formation (Hfº) data provided in the table below, calculate the change in enthalpy (H) for the
following reaction of the combustion of nitromethane, a common racing fuel.
4 CH3NO2(l)
A.
B.
C.
D.
E.
F.
3.
- 434 kJ
- 1070 kJ
- 1114 kJ
- 1292 kJ
- 1556 kJ
None of the above are correct.
+
3 O2(g)

2 N2(g) + 6 H2O(g)
Substance (state)
CH3NO2(l)
CO(g)
CO2(g)
H2O(l)
H2O(g)
+
4 CO2(g)
Hfº (kJ/mol)
- 434
- 111
- 394
- 286
- 242
A Twinkie is sent to the lab for determination of calorie content. It is burned in bomb calorimeter with a heat capacity
of 5.431 kJ/°C. The initial and final temperatures were 23.0°C and 138.0°C respectively. Calculate the heat (in food
calories or Calories) in one Twinkie?
A.
B.
C.
D.
E.
F.
4.
April 19, 2013
Which of the following reactions is correct for the standard enthalpy of formation (Hf°) for sulfur dioxide?
A.
B.
C.
D.
E.
F.
2.
EXAM III (100 PTS)
5.431
21.18
149.3
624.6
749.5
4184
As demonstrated in class, strontium salts burn with a brillant red flame. The wavelength of the light given off is 655
nm. Calculate the frequency (sec-1) of the red light.
A.
B.
C.
D.
E.
F.
1.95 x 102
6.55 x 102
4.58 x 105
4.58 x 1014
2.18 x 10-15
None of the above are correct.
5.
Which of the following orbital shapes can be described by n = 4, l = 0.
A.
B.
C.
D.
E. These quantum numbers do not decribe any orbital shape described above.
6.
How many electrons in an atom can have the following set of quantum numbers?
n = 3, ms = +1/2
A.
B.
C.
D.
E.
F.
7.
1
3
5
9
18
None of the above are correct.
Which of the following statements are true?
A. In Bohr’s atomic theory, when an electron moves from one energy level to another energy level more distant from
the nucleus, energy is emitted.
B. The principal quantum number determines the size and the shape of the orbitals.
C. Mendeleev assembled the periodic table according to the element’s electron configuration.
D. An s-orbital can accommodate more than two electrons when the atom is large.
E. The Pauli Exclusion Principle states that no two electrons in an atom can have the same four quantum
numbers.
F. None of the above statements are true.
8.
Which of the following sets of quantum numbers are not possible?
A.
B.
C.
D.
E.
n = 2, l = 1, ml = 0, ms= + ½
n = 2, l = 0, ml = -1, ms= - ½
n = 3, l = 2, ml = +1, ms= + ½
n = 3, l = 2, ml = +2, ms= - ½
n = 3, l = 1, ml = 0, ms= + ½
Problems (60 pts)
9.
(12 pts) Calculate the H for the following reaction:
P4O10 (s)
+
6 PCl5 (g)

10 Cl3PO (g)
when the following heats of reaction at 25ºC are known.
P4 (s)
 4 PCl3 (g)
+ 6 Cl2 (g)
P4 (s) + 5 O2 (g) 
PCl3(g) + ½ O2 (g )
10. (8 pts)



H = - 2967.3 kJ
P4O10 (s)
 PCl5 (g)
PCl3(g) + Cl2 (g )

H = - 1225.6 kJ

H =
 Cl3PO (g)

-84.2 kJ
H = - 285.7 kJ
H = - 610.1 kJ
Using a Born-Haber process and the information provided below, calculate the heat of sublimation (Hsub)
for solid magnesium. For full credit, either provide a Born-Haber Cycle diagram or a complete set of
chemical equations to explain the process of forming the ionic Mg-F bond.
Hdissociation F2(g)
+ 154 kJ/mol
Electron Affinity F(g)
- 328 kJ/mol
First Ionization Energy Mg(g)
+ 735 kJ/mol
Second Ionization Energy Mg(g)
+ 1445 kJ/mol
Hfo MgF2(s)
- 2088 kJ/mol
lattice energy (U)
- 3916 kJ/mol
Hsub = + 150. kJ
11. (10 pts) Using the energy formula below, where n is the principal quantum number and Z is the atomic number,
calculate the wavelength (in nanometers) when an electron falls from n = 3 to n = 1 in a Li2+ cation.
 2.18 x 10
En 
2
n
18
 = 11.4 nm
2
Z
Joules
12. (20 pts) From the following list, select the atom that most appropriately describes the statement. Atoms may be used
more than once or not at all.
Li, B, C, N, O, F, Kr, Na, K, Rb, Cs
A. largest atomic radius
Cs
B. nonmetal with the most unpaired electrons
N
C. lowest ionization energy
Cs
D. 4 valence electrons
C
-
E. most easily forms a 2 anion
F.
13. (8 pts)
14. (2 pts)
O
ns2np3 electron configuration
N
G. most positive electron affinity (H=most negative)
F
H. least reactive element
Kr
I.
least reactive alkali metal
Li
J.
metalloid (semi-metal)
B
Write the electron configuration for the following atoms/ions. DO NOT use the noble gas inner core
abbreviation. Show the arrangement (orbital box diagram) of all the electrons in the partially filled orbitals.
P
1s22s22p63s23p3 ___ ____ ____
Cr
1s22s22p63s23p64s1 _____ 3d5___ ____ ____ _____ ____
Se2-
1s22s22p63s23p64s23d104p6
Zn2+
1s22s22p63s23p64s03d10
Circle the atoms/ions below that would be predicted to have magnetic behavior.
P
Cr
Se2-
Zn2+
Important Constants
Solubility Rules (apply in order)
R = 0.08206 L-atm/mole-K
1 atmosphere = 760 torr = 760 mm Hg (exactly)
density of H2O = 1.00 g/mL

specific heat H2O = 4.184 J/gºC
1Cal = 1000 cal = 4.184 kJ
c = 3.00 x 108 m/s
h = 6.626 x 10-34 J-s
1.
2.
3.
4.
5.
6.
All Na+, K+, and NH4+ salts are soluble.
All NO3-, C2H3O2-, ClO3-, and C1O4- salts are soluble.
All Ag+, Pb2+ , and Hg22+ salts are insoluble.
All Cl- , Br- , and I- salts are soluble.
All CO32-, O2-, S2-, OH-, SO32-, CrO42-, Cr2O72-, and PO43salts insoluble, except CaS, SrS, BaS and Ba(OH)2.
All SO42- salts are soluble except Ca2+, Sr2+, and Ba2+.
Vapor Pressure of Water at Various Temperatures
T (oC)
0
5
10
12
14
16
17
18
19
20
P (torr)
4.58
6.54
9.21
10.52
11.99
13.63
14.53
15.48
16.48
17.54
T (oC)
21
22
23
24
25
26
27
28
29
30
P (torr)
18.65
19.83
21.07
22.38
23.76
25.21
26.74
28.35
30.04
31.82
T (oC)
35
40
45
50
55
60
65
70
80
90
P (torr)
42.2
55.3
71.9
92.5
118.0
149.4
187.5
233.7
355.1
525.8
T (oC)
92
94
96
98
100
102
104
106
108
110
P (torr)
567.0
610.9
657.6
707.3
760.0
815.9
875.1
937.9
1004.4
1074.6