university of kwazulu-natal, school of chemistry, durban centre

School of Chemistry
and Physics
Westville Campus,
Durban
BARCODE
CHEMICAL REACTIVITY - CHEM120
TEST 2
Date: Tuesday, 8 October 2013
Total marks: 25
Time: 17h45 – 18h30
IMPORTANT: Complete this part immediately.
Name:
Student No:
Tutorial Day:
Tutorial Venue:
Tutor’s Name:
INSTRUCTIONS:
1.
2.
Answer ALL questions.
For Section A which contains the multiple choice questions, write your
answers on the multiple choice answer sheet and follow the instructions
given in the question.
3.
4.
5.
Calculators may be used but all working must be shown.
The pages of this test must not be unpinned.
Your answers for Section B must be written on the question paper in the spaces
provided. The left-hand pages may be used for extra space or for rough work.
Marks will be deducted for the incorrect use of significant figures and the
omission of units.
You must write legibly in black or blue ink. Pencils and Tipp-Ex are not allowed.
This test consists of 9 pages. Please check that you have them all.
A data sheets and a periodic table are provided.
6.
7.
8.
9.
Question
No.
Mark
Section
A
1
2
3
4
5
10
4
3
2
2
4
Total
Mark
Final Percentage:
25
/25
%
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120: Chemical Reactivity
TEST 2: Tuesday, 8 October 2013
SECTION A - Multiple Choice Questions




For each of the following questions, select the correct answer from the list provided.
There is only one correct answer for each question.
Indicate your answer on the multiple choice answer sheet provided.
Make a dark heavy mark with HB pencil that fills the block of the appropriate letter
completely.
1. Which of the following changes is not exothermic?
(1)
A. Combustion of butane.
B. Freezing water.
C. Condensing steam.
D. Melting copper.
2. The specific heat capacity of water is 4.18 J K–1 g–1. What is the enthalpy change when
10.00 g of water is heated from 285.0 K to 300.0 K?
(1)
A. 2.79 J
B. 627 kJ
C. 6.27 kJ
D. 627 J
3. The heats of formation (ΔfHo ) at 298 K for SO2(g) and SO3(g) are 296.8 and –395.7 k J
mol–1 respectively. What is the enthalpy (ΔrHo) at 298 K per mole of SO2 for the
reaction: 2SO2(g) + O2(g) → 2SO3(g)
(2)
A + 98.9 kJ mol–1
B
–692.5 kJ mol–1
C  197.8 kJ mol–1
D
–98.9 kJ mol–1
2
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120: Chemical Reactivity
TEST 2: Tuesday, 8 October 2013
4. Which statement is incorrect about entropy?
(1)
A. A pure, perfect crystal has zero entropy at 0 K.
B. For a phase change, ΔS = 0.
C. The entropy of a system + surroundings increases during a spontaneous,
irreversible process.
D. The value of So for a compound or element depends on temperature.
5.
Which one of the following is a valid expression for the rate of the reaction below?
4NH3 + 7O2 → 4NO2 + 6H2O
(1)
A.
B.
C.
D.
6. Which transformation could take place at the anode of an electrochemical cell?
A. NO → NO3B. CO2 → Cr2O42C. VO2+ → VO2+
D. H2AsO4 → H3AsO3
3
(2)
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120: Chemical Reactivity
TEST 2: Tuesday, 8 October 2013
7.Which one of the following graphs shows the correct relationship between concentration
and time for a reaction that is second order in [A]?
(1)
A.
B.
C.
D.
8. The standard cell potential (E°cell) for the voltaic cell based on the reaction below is
__________ V.
(1)
Sn2+ (aq) + 2Fe3+ (aq) → 2Fe2+ (aq) + Sn4+ (aq)
A. +0.46
B. +0.617
C. +1.39
D. -0.46
End of Section A
4
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120: Chemical Reactivity
TEST 2: Tuesday, 8 October 2013
SECTION B
QUESTION 1
(4)
A mass of 100.0 g of water was placed in a constant-pressure calorimeter. The temperature of
the water was recorded as 295.0 K. A copper block of mass 20.0 g was heated to 353.0 K and
then dropped into the water in the calorimeter. What was the final temperature of the water if
the specific heat capacities of water and copper are 4.18 and 0.385 J K–1 g–1, respectively?
Solution
5
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120: Chemical Reactivity
TEST 2: Tuesday, 8 October 2013
QUESTION 2
(3)
Calculate the ΔH for the reaction
½ H2 (g) + ½ Cl2 (g)  HCl (g)
Given that:
ΔH = 47.5 kJ
⁄
ΔH = 105 kJ
⁄
ΔH = -402.5 kJ
Solution
ΔH = 47.5 kJ………..i
⁄
ΔH = 105 kJ………....ii
⁄
ΔH = -402.5 kJ………iii
To get ½ H2 (g) + ½ Cl2 (g)  HCl (g)
Reverse eqn ii, add eqns i and iii
⁄
ΔH = -105 kJ………....ii
⁄
⁄
[H = - 105 +47.5 + -402.5 = - 460 kJ]1/2
H = -230 kJ
6
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120: Chemical Reactivity
TEST 2: Tuesday, 8 October 2013
QUESTION 3
(3)
The reaction of iodide ions with hypochlorite ions, OCl- (the active ingrediant in a chlorine
bleach such as Jik), follows the equation
OCl- + I- → OI- + Cl- .
It is a rapid reaction that gives the following rate data:
Initial Concentration / mol dm-3
[OCl-]
[I-]
1.7 x 10-3
1.7 x 10-3
3.4 x 10-3
1.7 x 10-3
1.7 x 10-3
3.4 x 10-3
Rate of formation of Cl- / mol dm-3 s-1
1.75 x 104
3.50 x 104
3.50 x 104
What is the rate law for the reaction?
SOLUTION:
Rate = k [OCl-]a [I-]b
(
)
(
)
2 = 2a
a=1
2 = 2b
a=1
Rate = k [OCl-]1 [I-]1
7
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120: Chemical Reactivity
TEST 2: Tuesday, 8 October 2013
QUESTION 4
(2)
A voltaic cell is constructed that uses the following reaction and operates at 298 K:
Zn(s) + Ni2+(aq) → Zn2+(aq) + Ni(s)
The emf of this cell under standard conditions is +0.48 V. What is the emf of this cell when [Ni2+]
= 3.00 M and [Zn2+] = 0.10 M?
SOLUTION:
Anode (oxidation): Zn(s) → Zn2+(aq) + 2 eCathode (reduction): Ni2+(aq) + 2 e- → Ni(s)
R = 8.314 J mol-1 K-1
T = 298 K
F = 96485 J V-1 mol-1
[Ni2+] = 3.00 M
[Zn2+] = 0.10 M
n=2
Eºcell = 0.48 V
lnQ = 0.48 V -
= 0.52 V
QUESTION 5
(a)
Draw the structural formula of (E)-1-amino-2-butene and indicate whether it is a
primary (1°), secondary (2°), tertiary (3°) or quaternary (4°) amine.
(2)
NH2
8
Primary (1°) amine
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120: Chemical Reactivity
TEST 2: Tuesday, 8 October 2013
(b)
Give the IUPAC name for each of the following compounds:
(i)
3-ethyl-2,4-dimethylheptane
(ii)
O
3-methylpentan-2-one
9
(2)
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Durban
CHEM120: Chemical Reactivity
TEST 2: Tuesday, 8 October 2013
STANDARD REDUCTION POTENTIALS IN VOLTS AT 25 °C
F2(g) + 2e¯ ⇌ 2F-(aq)
Co3+(aq) + e¯ ⇌ Co2+(aq)
MnO4-(aq) + 8H+(aq) + 5e¯ ⇌ 4H2O + Mn2+(aq)
ClO4-(aq) + 8H+(aq) + 8e¯ ⇌ 4H2O + Cl¯(aq)
Cl2(g) + 2e¯ ⇌ 2Cl¯(aq)
Cr2O72-(aq) + 14H+(aq) + 6e¯ ⇌ 7H2O + 2Cr3+(aq)
MnO2(s) + 4H+(aq) + 2e¯ ⇌ 2H2O + Mn2+(aq)
O2(g) + 4H+(aq) + 4e¯ ⇌ 2H2O(l)
Br2(l) + 2e¯ ⇌ 2Br¯(aq)
NO3¯(aq) + 4H+(aq) + 3e¯ ⇌ 2H2O +NO(g)
Hg2+(aq) + 2e¯ ⇌ Hg(l)
Ag+(aq) + e¯ ⇌ Ag(s)
Fe3+(aq) + e¯ ⇌ Fe2+(aq)
MnO4¯(aq) + 2H2O + 3e¯ ⇌ 4OH¯(aq) + MnO2(s)
I2(s) + 2e¯ ⇌ 2I¯(aq)
Cu2+(aq) + 2e¯ ⇌ Cu(s)
Sn4+(aq) + 2e¯ ⇌ Sn2+(aq)
2H+(aq) + 2e¯ ⇌ H2(g)
Pb2+(aq) + 2e¯ ⇌ Pb(s)
Sn2+(aq) + 2e¯ ⇌ Sn(s)
Ni2+(aq) + 2e¯ ⇌ Ni(s)
Cd2+(aq) + 2e¯ ⇌ Cd(s)
Fe2+(aq) + 2e¯ ⇌ Fe(s)
Zn2+(aq) + 2e¯ ⇌ Zn(s)
Mn2+(aq) + 2e¯ ⇌ Mn(s)
Al3+(aq) + 3e¯ ⇌ Al(s)
Mg2+(aq) + 2e¯ ⇌ Mg(s)
Na+(aq) + e¯ ⇌ Na(s)
Ca2+(aq) + 2e¯ ⇌ Ca(s)
Li+(aq) + e¯ ⇌ Li(s)
10
E°
+ 2.85
+ 1.82
+ 1.52
+ 1.39
+ 1.36
+ 1.33
+ 1.23
+ 1.23
+ 1.06
+ 0.96
+ 0.85
+ 0.80
+ 0.77
+ 0.59
+ 0.54
+ 0.34
+ 0.15
0.00
– 0.13
– 0.14
– 0.24
– 0.40
– 0.44
– 0.76
– 1.18
– 1.66
– 2.34
– 2.71
– 2.87
– 3.04
1
18
1
2
H
He
1.008
2
3
4
5
6
7
8
9
10
Li
Be
B
C
N
O
F
Ne
6.941
9.012
10.81
12.01
14.01
16.00
19.00
20.18
11
12
13
14
15
16
17
18
Na
Mg
22.99
24.31
13
Periodic Table
3
4
5
6
7
8
9
10
11
12
14
15
16
17
4.003
Al
Si
P
S
Cl
Ar
26.98
28.09
30.97
32.07
35.45
39.95
36
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
39.10
40.08
44.96
47.88
50.94
52.00
54.94
55.85
58.93
58.69
63.55
65.39
69.72
72.61
74.92
78.96
79.90
83.80
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
85.47
87.62
88.91
91.22
92.91
95.94
98.91
101.1
102.9
106.4
107.9
112.4
114.8
118.7
121.8
127.6
126.9
131.3
55
56
57*
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
Cs
Ba
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
132.9
137.3
138.9
178.5
180.9
183.8
186.2
190.2
192.2
195.1
197.0
200.6
204.4
207.2
209.0
(209)
(210)
(222)
87
88
89* *
104
105
106
107
108
109
Fr
Ra
Ac
Db
Jl
Rf
Bh
Hn
Mt
(223)
(226)
(227)
(261)
(262)
(263)
(262)
(?)
(?)
*
Lanthanide
Series
**
Actinide
Series
58
59
60
61
62
63
64
65
66
67
68
69
70
71
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
140.
1
140.
9
144.
2
(147)
150.
4
152.
0
157.
2
158.
9
162.
5
164.
9
167.
3
168.
9
173.
0
175.
0
90
91
92
93
94
95
96
97
98
99
100
101
102
103
Th
Pa
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lr
(232)
(231)
(238)
(237)
(239)
(243)
(247)
(247)
(252)
(252)
(257)
(256)
(259)
(260)
11
DATA SHEET
Physical Constants
Conversion Factors
-23
Boltzmann constant
Planck constant
Elementary charge
Speed of light in vacuum
k
h
e
c
Avogadro constant
Gas constant
L or NA
R = kL
Molar volume of an ideal gas
V
o
m
-1
Vm
Faraday constant
Atomic mass unit (amu)
Rest mass of electron
Rest mass of proton
Rest mass of neutron
Vacuum permittivity
Standard acceleration
of free fall
Rydberg constant
for the H atom
-1
= 1.381 x 10 J K
-34
= 6.626 x 10 J s
-19
= 1.602 x 10 C
8
-1
= 2.998 x 10 m s
10
-1
= 2.998 x 10 cm s
23
-1
= 6.022 x 10 mol
-1
-1
= 8.315 J K mol
-1
-1
= 8.315 L kPa K mol
-1
-1
= 0.08206 L atm K mol
-1
= 22.414 L mol
(at 1.000 atm and 273.2 K)
F = eL
u
me
mp
mn
ευ
= 24.789 L mol
(at 100.0 kPa and 298.2 K)
4
-1
= 9.6485 x 10 C mol
-27
= 1.661 x 10 kg
-31
= 9.109 x 10 kg
-27
= 1.673 x 10 kg
-27
= 1.675 x 10 kg
-12 -1
2
-1
= 8.854 x 10 J C m
g
= 9.807 m s
RH
= 109677 cm
-6
= 10 m = 1 μm
-10
= 1 x 10 m = 0.1 nm = 100 pm
-3
3
3
= 10 m = 1 dm
5
-2
5
= 1.013 x 10 N m = 1.013 x 10 Pa
= 760 mmHg = 760 Torr
5
= 1.000 x 10 Pa
= 0.2390 cal
3
2
-2
= 1 Pa m = 1 m kg s
= 4.184 J
-19
= 1.602 x 10 J
= 101.3 J
-1
=1Js
-1
-1
= 1 μg g = mg kg
-1
= 1 mg L (dilute aqueous solutions only)
= 1000 kg
1 micron (μ)
1 Ångström (Å)
1L
1 atm
1 bar
1J
1 cal
1 eV
1 L atm
1W
1 ppm
1 tonne
-2
-1
Prefixes to Units
P
T
G
M
k
d
c
m
μ
n
p
f
peta
tera
giga
mega
kilo
deci
centi
milli
micro
nano
pico
femto
10
15
10
12
10
9
10
6
10
3
10
12
-1
10
-2
10
-3
10
-6
10
-9
10
-12
10
-15

Download Report