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CHEM 4:011 – PRINCIPLES OF CHEMISTRY I
EXAM #2
(30 QUESTIONS, 1½ HOURS)
13October2005
FORM A
1. Calculate
Δ
H for the reaction, N
2
O(g)
+
NO
2
(g)
→
3NO(g), using Hess’s law
and the following data:
N
2
(g)
+
O
2
(g)
→
2NO(g)
Δ
H = +180.7 kJ
2NO(g)
+
O
2
(g)
→
2NO
2
(g)
Δ
H = 113.1 kJ
2N
2
O(g)
→
2N
2
(g)
+
O
2
(g)
Δ
H = 163.2 kJ
(A) +246.0 kJ
(B) 95.6 kJ
(C) +155.6 kJ
(D) +130.6 kJ
(E) 276.3 kJ
2.
Phosgene decomposes according to the reaction,
COCl
2
(g )
'
CO(g)
+
Cl
2
(g)
where K
p
= 0.0431 at a certain temperature.
A pressure of 0.75 atm of COCl
2
is introduced into a container and allowed to come to equilibrium.
What is the
partial pressure of CO(g) at equilibrium?
(A) 0.043 atm
(B) 0.16 atm
(C) 0.21 atm
(D) 0.32 atm
(E) 0.75 atm
3.
One million molecules of each of the following gases are simultaneously
injected into the atmosphere at the back of a room.
For which gas will the
greatest
amount of time lapse before 100 of its molecules will have struck the
wall at the front of the room?
(A) Cl
2
(B) CH
4
(C) NO
2
(D) CO
2
(E) NH
3
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Of the following, which one is impossible for an ideal gas?
(A) V
1
/
T
1
=
V
2
/
T
2
(B) V
1
T
1
=
V
2
T
2
(C) V
1
/
V
2
=
T
1
/
T
2
(D) V
2
=
T
2
V
1
/
T
1
(E) V
1
/
V
2
=
P
2
/
P
1
5.
Cold packs, whose temperatures are lowered when ammonium nitrate
dissolves in water, are carried by athletic trainers when transporting ice is not
possible. Which of the following is true of this reaction?
(A)
Δ
H < 0, process is exothermic
(B)
Δ
H > 0, process is exothermic
(C)
Δ
H < 0, process is endothermic
(D)
Δ
H > 0, process is endothermic
(E)
Δ
H = 0, since cold packs are sealed
6.
If a cubic centimeter of gas at 25ºC contains exactly one million molecules,
what is the pressure of this gas in torr?
( R = 0.08206 L·atm/mol·K )
(A) 2.59 × 10
12
torr
(B) 1.86 × 10
13
torr
(C) 4.06 × 10
14
torr
(D) 3.09 × 10
11
torr
(E) 3.09 × 10
14
torr
7. Consider the following equilibrium:
2 SO
2
(g)
+
O
2
(g)
'
2 SO
3
(g)
The chemical equilibrium cannot be established when ______ is/are placed in
a 1.0 L container:
(A) 0.25 mol SO
2
(g) and 0.25 mol of O
2
(g)
(B) 0.25 mol SO
2
(g) and 0.25 mol of SO
3
(g)
(C) 0.50 mol O
2
(g) and 0.50 mol of SO
3
(g)
(D) 0.75 mol SO
2
(g)
(E) 1.0 mol SO
3
(g)
8.
At times liquids other than mercury are used in manometers.
Dinoctyl
phthalate was used in a closedend manometer and the observed
Δ
h was
5.68 cm.
Assuming the vapor pressure of this phthalate is negligible, and the
densities of mercury and dinoctyl phthalate are 13.55 and 0.984 g/mL,
respectively, what was the pressure of the gas being measured?
(A) 78.2 torr
(B) 782 torr
(C) 56.8 torr
(D) 0.412 torr
(E) 4.12 torr
9.
Which one of the following will result in a shift in the equilibrium position to the
right?
C(s)
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 Spring '08
 Larsen
 Reaction

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