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Chem. 1B Final Practice
Name__________________________________________
Student Number _________________________________
All work must be shown on the exam for partial credit. Points will be taken off for
incorrect or no units and for the incorrect number of significant figures. Calculators are
allowed. On short answer problems you must show your work in order to receive credit
for the problem. If your cell phone goes off during the exam you will have your exam
removed from you.
Fundamentals (of 60 possible)
Problem 1 (of 16 possible)
Problem 2 (of 7 possible)
Problem 3 (of 17 possible)
Problem 4 (of 11 possible)
Problem 5 (of 12 possible)
Problem 6 (of 17 possible)
Multiple Choice (of 60 possible)
Extra Credit (of 5 possible)
Final Total (of 200 possible)
2
Fundamental Questions Each of these fundamental chemistry questions is worth 5 points. You must show work
to get credit. Little to no partial credit will be rewarded. Make sure to report answers in
the correct number of significant figures and with the proper units.
1) 5 pts Draw a heating curve (Temperature vs. Heat Supplied) of H2O. Make sure
to include the value of the temperatures at boiling and freezing, clearly label
where H2O is a solid, a liquid, and a gas and indicate where ΔHvap and ΔHfus
are located.
2)
5 pts
In class we had a balloon filled with H2(g) and O2(g). The balloon did not
appear to undergo a chemical reaction until it was touched by a lit candle.
At this point the balloon turned into a fireball. Students in the front row
could feel heat from the fireball. The reaction was determined to be
O2(g) +2H2(g) 2H2O(g). Determine the signs of the following:
w<0 w>0 w=0 volume decreases
q<0 q>0 q=0 q= ΔH at constant P
ΔH<0 ΔH>0 ΔH=0 exothermic
ΔS<0 ΔS>0 ΔS=0
ΔG<0 ΔG>0 ΔG=0 spontaneous
3) 5 pts The following data was collected for the reaction
A + B C + D Ea=161molkJ
k=1.94×10-4
smolL at 30.0°C
What is k at 40.0°C?
smolL
molKJ
molJ
smolL
a
k
k
TTR
E
k
k
00149.0
2.313
1
2.303
1
3145.8
161000
1094.1ln
11ln
2
4
2
211
2
3
4) 5 pts What is wavelength associated with an electron traveling at 3.0×107
sm ?
mkgmv
h
sm
11
731
34
104.2100.31010939.9
10626.6
5) 5 pts Determine the number of orbitals that can have the following designation
3f
When n=3 l cannot equal 3 therefore no orbitals can
have this designation
n = 2
l = 0 ml = 0
l = 1 ml = -1,0,1
4 orbital
Determine the number of electrons that can have the following designation
3dz2
n=3 l=2 ml = 1 value
ms = ± ½
2 electrons
6d
n=6 l=2
ml = -2,-1,0,1,2 ms = ± ½
10 electrons
6) 5 pts Identify if the following reactions are redox reactions or not. If they are
redox reactions, specify what is oxidized and what is reduced.
Cu(OH)2(s) + 2HNO3(aq) Cu(NO3)2(aq) + 2H2O(l)
Not a redox reaction
Fe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g)
Redox Reaction
Fe +30 gained electrons
Fe is reduced
C +2 +4 lost electrons
C is oxidized
4
7) 5 pts Determine the rate law from the following mechanism.
H2S ⇌ H+ + HS
- fast equilibrium
Cl2 + HS- H
+ + 2Cl
- + S slow
Indicate if the reaction contains intermediates or catalysts and which
substances they are.
There are no catalysts and HS- is an intermediate
Rate= k2[Cl2][HS-]
Eliminate the intermediate
k1[H2S]=k-1[H+][HS
-]
H
SHClRate
H
SHHS
k
kk
k
k
22
2
1
12
1
1
8) 5 pts Circle the option that best fits each of the following descriptions:
Smallest atomic radius Na Si S Al
Largest ionic radius Na+ O
2- Mg
2+ F
-
Least polar bond C-N C-O O-H
Greatest electronegativity Al C Na N
Smallest first ionization energy K Na Mg
9) 5 pts Determine if energy is absorbed or emitted when an electron transitions
from the n=7 to the n=2 level of C5+
and the wavelength of the photon
associated with the transition?
Energy is emitted
|Energy of the transition| = energy of photon
Energy of transition
JJE
n
Z
n
ZJE
if
17
2
2
2
218
2
2
2
218
1080.17
6
2
610178.2
10178.2
Energy of photon
m
J
Js
E
hc
hcE
sm
8
17
834
1010.11080.1
1000.310626.6
5
10) 5 pts A piece of iron of mass 20.0 g at 100.°C is placed in a vessel of negligible
heat capacity but containing 50.7 g of water at 22.0°C. Calculate the final
temperature of the water. Assume that there is no energy lost to the
surroundings.
CT
CTOgHCTgFe
TmCq
f
fCgJ
fCgJ
p
watermetal
25
0.2218.47.50.10045.00.20 2
11)
5 pts
What is ΔS for 2.00 mol of CO2 undergoing the following reaction at
constant pressure CO2(s,150 K) CO2(g, 195 K)?
Given the following data: Tsub = 195 K, ΔHsub =25.2molkJ ,
molK
JP sCO
C 11.47)(2
, and molK
JP gCO
C 8.34)(2
ΔS to take CO2 to sublimation point
KJ
molKJ
K
Kmol
T
TnCS 8.24
150
195ln11.4700.2ln
1
2
ΔS of sublimation (constant temperature)
KJ
KkJmol
kJsubrev
K
mol
T
Hn
T
qS 258258.0
.195
2.2500.2
KJ
KJ
KJS 2832588.24
12) 5 pts What wavelength of light is needed to excite an e- from the ground state of
a particle in a box that is 5.00×10-7
m long to the n=5 state?
Calculate the energy need for an e- to go from n=1 n=5
Jmkg
Jsnn
mL
hE if
2422
2731
23422
2
2
1078.5151000.51010939.98
10626.6
8
Calculate the wavelength of the photon
m
J
Js
E
hc Sm
0344.01078.5
10998.210626.624
834
6
Short Answer Questions
Each of the following short answer questions are worth the noted points. Partial credit
will be given. Make sure to show work, report answers to the correct number of
significant figures and use the proper units.
1a) 5 pts Consider the galvanic cell based on the following half-reactions:
Au3+
+ 3e- Au E° = 1.50 V
Tl+ + e
- Tl E° = -0.34 V
Determine the overall cell reaction and calculate E°cell.
For galvanic cell E° must be positive
Au3+
+3e- Au E° = 1.50 V
3(Tl Tl+ + e
-) E° = 0.34 V
Au3+
(aq) + 3Tl(s) Au(s) + 3Tl+(aq) E° = 1.50 V+0.34 V=1.84V
1b) 5 pts Calculate ΔG° and K for the cell reaction at 25°C.
molkJ
molJ
molC VnFEG 5321032.584.1964853 5
931026.2
ln964853
2983145.884.1
ln
K
KK
V
KnF
RTE
molC
molKJ
1c) 6 pts Calculate Ecell at 25°C when [Au
3+] =1.0×10
-2 M and [Tl
+] = 1.0×10
-4 M.
V
KVE
Au
Tl
nF
RTEK
nF
RTEE
molC
molKJ
04.2100.1
100.1ln
964853
2983145.884.1
lnln
2
34
3
3
7
2) 7 pts It takes 208.4 kJ of energy to remove one mol of electrons from the atoms
on the surface of rubidium metal. If rubidium metal is irradiated with
254-nm light, what is the maximum kinetic energy the released electrons
can have?
Calculate energy of 254 nm light
mnm
mnm 7
91054.2
10
1254
Hzm
c
c
sm
15
7
8
1018.11054.2
10998.2
JHzJshE 191534 1082.71018.110626.6
This is the energy that 1 electron would have.
Calculate the energy needed to remove 1 e-.
1922
231047.31047.3
10022.6
14.208
1
kJ
e
mol
NE
molkJ
A
Subtract the energy needed to remove the e-from the energy
provided by photon. This will give the max energy for KE.
JJJKE 191919 1035.41047.31082.7
8
3a) 6 pts For each of the following
1) Write out the Lewis dot structure including all relevant resonance
structures. Make sure all structures have minimized formal charges.
2) Assign formal charges to every atom.
XeOF4
1)
2) All Formal Charges are 0
3b) 6 pts NO3-
1)
2) Formal Charges
Structure 1 (0,1,-1,-1)
Structure 2 (-1,1,0-1)
Structure 3 (-1,1,-1,0)
3c) 5 pts The following Lewis structure was drawn for a Period 3 element. Identify
the element
Since the formal charges on each of the O atoms are 0 and the
formal charge on each of the Cl atoms is 0. Therefore the formal
charge on “?” must be 0 in order for the overall charge to be 0.
This means that “?” must have 6 valence electron which makes it
an S atom.
9
4a) 6 pts The bromination of acetone is acid-catalyzed:
CH3COCH3 + Br2 H CH3COCH2Br + H
+ + Br
-
[CH3COCH3]o (M) [Br2]o (M) [H
+]o (M)
Rate of Disappearance
of Br2( Lsmol )
0.30 0.050 0.050 5.7×10-5
0.30 0.10 0.050 5.7×10-5
0.30 0.050 0.10 1.2×10-4
0.40 0.050 0.20 3.1×10-4
0.40 0.050 0.050 7.6×10-5
What is the rate law? zyx HBrCOCHCHkrate ][][][ 233
Determine reaction order with respect to CH3COCH3
Use experiments 1 and 5
1
75.0log75.0log
75.040.0
30.075.0
050.0050.040.0106.7
050.0050.030.0107.55
5
x
x
M
M
MMMk
MMMk
x
x
x
zyx
Ls
mol
zyx
Ls
mol
zy HBrCOCHCHkrate ][]][[ 233
Determine reaction order with respect to Br2
Use experiments 1 and 2
When the [Br2] is double and the concentration of
[CH3COCH3] and [H+] remains the same the rate does not
change. Therefore, reaction is 0th
order with respect to [Br2]. zHCOCHCHkrate ]][[ 33
Determine reaction order with respect to H
+
Use experiments 4 and 5
1
00.4log08.4log
0.4050.0
20.008.4
050.040.0106.7
20.040.0101.35
4
z
z
M
M
MMk
MMk
z
z
z
z
Ls
mol
z
Ls
mol
]][[ 33
HCOCHCHkrate
4b) 5 pts If the rate law was determined to be
27.0
233 ][]][[ HBrCOCHCHkrate
And the following data was collected
[CH3COCH3]o (M) [Br2]o (M) [H+]o (M)
Rate of Disappearance
of Br2( Lsmol )
0.50 0.20 0.050 6.3×10-4
What is k? Remember to include units.
smol
L
Ls
mol
k
MMMk
HBrCOCHCHkrate
3.1
3.1
16.0
050.020.050.0103.6
][]][[
27.0.4
27.0
233
10
5a) 4 pts What is the electron configurations and number of unpaired e- of:
Po
Po = [Xe]6s24f
145d
106p
4 2 unpaired e
-
5b) 4 pts What is the electron configurations and number of unpaired e- of:
As2-
As2-
= [Ar]4s23d
104p
5 1 unpaired e
-
5c) 4 pts An ion having a 4+ charge and a mass of 8.286×10
-26 kg has two s electrons
with n=1, eight electrons with n = 2, and nine electrons with n = 3.
What is the atomic number of the ion?
This ion has a total of
2+8+9=19 e-
Because the charge on the ion is 4+, the ion must have 4 more
protons than electrons; therefore, the atomic number of the ion is
23, making it vanadium.
11
6a) 8 pts A technician carries out the reaction 2SO2(g) + O2(g) 2SO3(g) at 25°C
and 1.00 atm in a constant-pressure cylinder fitted with a piston. Initially,
0.0300 mol SO2 and 0.0300 mol O2 are present in the cylinder. The
technician then adds a catalyst to initiate the reaction. How much work
takes place, and is it done by the system or on the system. Assume that the
reaction goes to completion and the temperature of the system is constant.
VPw Determine the change in volume
Determine initial volume
Latm
Kmol
P
nRTV
nRTPV
molKLatm
47.100.1
29808206.00600.0
Determine final volume
Determine the limiting reagent
2
2
22 0150.0
2
10300.0 molO
molSO
molOmolSO
SO2 is the limiting reagent. All of the SO2 will be used up.
remainwillmolOmolOmolO 222 0150.00150.00300.0
formwillmolSOmolSO
molSOmolSO 3
2
3
2 0300.02
20300.0
Total moles of gas in the container after the reaction comes to completion
molmolmol 0450.00300.00150.0
Determine the volume
L
atm
Kmol
P
nRTV molK
Latm
10.100.1
29808206.00450.0
Calculate work
3
333
00037.0100
1
1
1037.047.110.1 m
cm
m
L
cmLLLV
Paatm
PaatmP 101325
1
10132500.1
JmPaVPw 3700037.0101325 3
Work is done on the system
6b) 5 pts What is the change in enthalpy for the reaction in J?
molkJ
molkJ
molkJ
molkJ
rxn
fffrxn
ffrxn
H
OHSOHSOHH
reacHprodHH
198)0()297(2)396(2
22 223
This is the amount of heat released when 1 mole of O2 reacts with 2 mol of SO2
Calculate ΔH for 0.015 mol O2
JkJmolO
kJmolO 4
2
2 100.30.31
198015.0
6c) 4 pts What is the change in internal energy for the reaction in J? Since the reaction takes place at constant pressure ΔH = q
JJJwqE 44 100.337100.3
12
Multiple Choice Questions Each of the following multiple choice questions are worth 5 points.
Your answers need to be filled in on the Scantron provided. Note: Your Scantrons will not be returned to you, therefore, for
your records, you may want to mark your answers on this sheet.
On the Scantron you need to fill in your perm number, test version,
and name. Failure to do any of these things will result in the loss
of 1 point. Your perm number is placed and bubbled in under the
“ID number”. Do not skip boxes or put in a hyphen. In addition,
leave bubbles blank under any unused boxes. The version number
(A) is bubbled in under the “test form.”
1. As the number of bonds between two carbon atoms increases, which one of the
following decreases?
A) the bond energy
B) the bond length
C) the number of electrons between the carbon atoms
D) all of these
E) none of these
2. Of the following five ions or molecules, which is the strongest reducing agent?
A) Cl2
B) Fe2+
C) Cr2+
D) F-
E) H2
3. Ammonium metavanadate reacts with sulfur dioxide in acidic solution as follows
(hydrogen ions and H2O omitted):
xVO3
– + ySO2 xVO
2+ + ySO4
2–
The ratio x : y is
A) 2 : 1
B) 1 : 1
C) 1 : 3
D) 1 : 2
E) None of the Above
4. Cations are _________ than/as their parent atom.
A) the same size
B) larger
C) smaller
13
5. Which of the following statements is(are) true?
I. An excited atom can return to its ground state by absorbing electromagnetic radiation.
II. The energy of an atom is increased when electromagnetic radiation is emitted from it.
III. The energy of electromagnetic radiation increases as its frequency increases.
IV. An electron in the n = 4 state in the hydrogen atom can go to the n = 2 state by
emitting electromagnetic radiation at the appropriate frequency.
V. The frequency and wavelength of electromagnetic radiation are inversely
proportional to each other.
A) III, IV, V
B) I, II, IV
C) II, III, IV
D) III, V
E) I, II, III
6. Which of the following statements is false?
A) The spin quantum number of an electron must be either +1/2 or –1/2.
B) An orbital can accommodate at most two electrons.
C) In the usual order of filling, the 6s orbital is filled before the 4f orbital.
D) The electron density at a point is proportional to 2 at that point.
E) A 2p orbital is more penetrating than a 2s; that is, it has a higher electron density
near the nucleus and inside the charge cloud of a 1s orbital.
7. The following reaction has a G° value of 42.6 kJ/mol at 25°C.
HB(aq) + H2O(l) H3O+(aq) + B
–(aq)
Calculate Ka for the acid HB.
A) 3.41 10–8
B) 14.0
C) 42,600
D) –17.2
E) 1.63
8. Consider an atom traveling at 1% of the speed of light. The de Broglie wavelength is
found to be 3.31 10–3
pm. Which element is this?
A) P
B) He
C) Ca
D) F
E) Be
14
9. Using the following bond energies:
Bond Bond Energy (kJ/mol)
CC 839
C-H 413
O=O 495
C=O 799
O-H 467
estimate the heat of combustion for 1 mol of acetylene:
C2H2(g) + 5/2O2(g) 2CO2(g) + H2O(g)
A) –447 kJ
B) +365 kJ
C) –1228 kJ
D) 1228 kJ
E) +447 kJ
10. At constant pressure, the reaction
2NO2(g) N2O4(g)
is exothermic. The reaction (as written) is
A) never spontaneous.
B) always spontaneous.
C) spontaneous at low temperatures but not at high temperatures.
D) spontaneous at high temperatures but not at low temperatures.
11. At 25°C, the following heats of reaction are known:
2C2H2 + 5O2 4CO2 + 2H2O H = –2600.0 kJ
C + O2 CO2 H = –394 kJ
2H2 + O2 2H2O H = –572 kJ
At the same temperature, calculate H for the following reaction:
2C + H2 C2H2 H = ?
A) 2422 kJ
B) 226 kJ
C) -2422kJ
D) -226 kJ
E) none of these
12. The rate constant k is dependent on
A) the temperature.
B) the concentration of the reactant.
C) the order of the reaction.
D) the concentration of the product.
E) none of these