G nh 3 titrated by a strong acid eg hno 3

e.g., NH
3
titrated by a strong acid, e.g., HNO
3
. Confirmation of this is the
equivalence point, approximately 5. The equivalence point of NH
3
and HNO
3
is
approximately 5.

Chem 162-2012 final exam + solutions 37
36 Chem 162-2012 Final Exam + Answers
Chapter 18 - Thermodynamics
Free energy calculations
Use the given data at 298 K to calculate ∆ G° for the reaction
2Cl
2
(g) + SO
2
(g) → SOCl
2
(g) + Cl
2
O(g)
Substance: Cl
2
( g ) SO
2
( g ) SOCl
2
( g ) Cl
2
O( g )
Δ H °
f
(kJ/mol):
0 –296.8 –212.5 80.3
S °(J/K • mol): 223.0 248.1 309.77 266.1
A) 129.3 kJ
B) 133.6 kJ
C) 196.0 kJ
D
) 199.8 kJ
E) 229.6 kJ
Δ H
o
= (-212500 + 80300) – ((2x0) -296800) = 1.646 x 105 J
Δ S
o
= (309.77 + 266.1) – ((2x223.0) + 248.1) = -118.23/K
Δ G
o
= Δ H
o
- T Δ S
o
Δ G
o
= (1.646 x 105) – (298 x -118.23) = 1.9983 x 105J = 199.83 kJ

Chem 162-2012 final exam + solutions 38
SECTION 4
Covers material not covered on the other exams
37 Chem 162-2012 Final Exam + Answers
Chapter 20 – Nuclear Chemistry
Radioactive decay kinetics
92
238
U undergoes alpha decay with a half-life of 4.5 x 10
9
years. What is the instantaneous
rate of decay for a 1.0 g sample of
92
238
U? 3.156 x 10
7
sec = 1 year.
A
. 1.2 x 10
4
nuclei
sec
B. 520
nuclei
sec
C. 4.32 x 10
6
nuclei
sec
D. 8.2 x 10
3
nuclei
sec
E. 2.4 x 10
9
nuclei
sec
Begin by finding λ
t
1/2
= 0.693/ λ
(4.5x109y x (3.156x107s/y)) = 0.693/ λ
λ = 4.88 x 10
-18
The answer options are in nuclei per second. Therefore, convert 1.0g into atoms (i.e.,
convert grams into nuclei).
1.0g x (1mol/238g) x (6.022x10
23
atom/mol) = 2.53 x 10
21
atoms
238
92
U
Instantaneous rate = λ [N]
Instantaneous rate = 4.88 x 10
-18
x (2.53x10
21
) = 1.23 x 10
4
atom/s

Chem 162-2012 final exam + solutions 39
38 Chem 162-2012 Final Exam + Answers
Chapter 20 – Nuclear Chemistry
Miscellaneous
The purpose of control rods in nuclear reactors is

Chem 162-2012 final exam + solutions 40
39 Chem 162-2012 Final Exam + Answers
Chapter 19 – Electrochemistry
Free energy, equilibria and cell potential calculations/Nernst equation
A concentration cell consists of two Al/Al
3+
electrodes. The electrolyte in compartment A is
0.050 M Al(NO
3
)
3
and in compartment B is 1.25 M Al(NO
3
)
3
. What is the voltage of the
cell at 25°C?
-

Chem 162-2012 final exam + solutions 41
40 Chem 162-2012 Final Exam + Answers
Chapter 20 – Nuclear Chemistry