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Chapter 16: Thermodynamics: Entropy, Free Energy, and Equilibrium
Problem Solving Center
Self Quiz 2
Self Quiz 2
This activity contains 20 questions.
The initial conditions for the forward reaction N
2
O
4
---> 2NO
2
(
g
) is matched correctly with its classification as a spontaneous or nonspontaneous reaction in (K
p
= 0.11)
P
N
2
O
4
= 0.010 atm, P
NO
2
= 1.0 atm : spontaneous.
P
N
2
O
4
= 0.10 atm, P
NO
2
= 10.0 atm : spontaneous.
P
N
2
O
4
= 1.0 atm, P
NO
2
= 1.0 atm : spontaneous.
P
N
2
O
4
= 1.0 atm, P
NO
2
= 0.010 atm : nonspontaneous.
P
N
2
O
4
= 10.0 atm, P
NO
2
= 0.10 atm : spontaneous.
The process which most likely results in a
decrease
in entropy is
S
8
(
s
) + 8O
2
(
g
) ---> 8SO
2
(
g
).
Mg(OH)
2
(
s
) ---> MgO(
s
) + H
2
O(
g
).
Br
2
(
l
) ---> Br
2
(
aq
).
H
2
CO
3
(
aq
) ---> H
2
O(
l
) + CO
2
(
g
).
2SO
2
(
g
) + O
2
(
g
) ---> 2SO
3
(
g
).
The phase change that is
incorrectly
matched with its entropy change is
liquid ---> gas : change in entropy > zero.
liquid ---> solid : change in entropy > zero.
solid ---> gas : change in entropy > zero.
gas ---> liquid : change in entropy < zero.
solid ---> liquid : change in entropy > zero.
The arrangement of 4 molecules in connected flasks labeled #1 and #2 has the highest entropy in
4 molecules in any 1 flask.
2 molecules in each of 2 flasks.
3 molecules in flask #1 and 1 molecule in flask #2.
4 molecules in flask #1.
3 molecules in a flask and 1 molecule in another flask.
The change that (at constant pressure) is most likely to produce the largest change in entropy is
(melting point of ethanol = -117 °C; boiling point of ethanol = 78 °C)
cooling 10.0 g of ethanol from 92 °C to 72 °C.
heating 10.0 g of ethanol from 85 °C to 105 °C.
cooling 10.0 g of ethanol from 65 °C to 45 °C.
heating 10.0 g of ethanol from -186 °C to -166 °C.
cooling 10.0 g of ethanol from -110 °C to -120 °C.
The standard entropy change for the reaction Fe
2
O
3
(
s
) + 3H
2
(
g
) ---> 2Fe(
s
) + 3H
2
O(
g
) is (S° of Fe
2
O
3
(
s
) = 87.4 J/(mol·K) ; S° of H
2
(
g
) = 130.6 J/(mol·K); S° of Fe(
s
) = 27.3 J/(mol·K); S° of H
2
O(
g
) = 188.7 J/(mol·K))
141.5 J/K.
2.0 J/K.
-141.5 J/K.
478.7 J/K.
-2.0 J/K.
If the standard entropy change for the reaction 2Ag
+
(
aq
) + SO
4
2-
(
aq
) ---> Ag
2
SO
4
(
s
) is 34.6 J/K, then the standard molar entropy for Ag
2
SO
4
(
s
) is (S° for Ag
+
= 72.7 J/(mol·K) and S° for SO
4
2-
= 20 J/(mol·K))
-200.0 J/(mol·K).
200.0 J/(mol·K).
127.3 J/(mol·K).
130.8 J/(mol·K).
-127.3 J/(mol·K).
The reaction that is
incorrectly
matched with the sign of the standard entropy of reaction for that reaction is
C
2
H
5
OH(
g
) ---> C
2
H
5
OH(
l
) : -122 J/K.
CaC
2
(
s
) + H
2
O(
l
) ---> C
2
H
2
(
g
) + CaO(
s
) : 100.6 J/K.
C
2
H
2
(
g
) + HCl(
g
) ---> CH
2
CHCl(
g
) : -123.7 J/K.
AgI(
s
) ---> Ag
+
(
aq
) + I
-
(
aq
) : 69 J/K.
2Na(
s
) + Cl
2
(
g
) ---> 2NaCl(
s
) : 181.2 J/K.
A
nonspontaneous
reaction at 298 K will result when the
enthalpy of reaction = 15.3 kJ, entropy of reaction = 87 J/K.
enthalpy of reaction = 23 kJ, entropy of reaction = 55 J/K.
enthalpy of reaction = -114.5 kJ, entropy of reaction = -298 J/K.
enthalpy of reaction = -12.5 kJ, entropy of reaction = -13 J/K.
enthalpy of reaction = -4.5 kJ, entropy of reaction = 17 J/K.
At what temperature (°C) is the reaction CO(
g
) + 2H
2
(
g
) ---> CH
3
OH(
g
) at equilibrium? (enthalpy of formation for CO(
g
) = -110.5 kJ/mol; enthalpy of formation for CH
3
OH(
g
) = -201.2 kJ/mol; S° for CO(
g
) = 197.6 J/(mol·K); S° for H
2
(
g
) = 130.6 J/(mol·K) ; S° for CH
3
OH(
g
) = 238.0 J/(mol·K))
411 °C
-232 °C
1006 °C
733 °C
138 °C
Which statement concerning changes in free energy and total entropy changes is
not
true?
If the total entropy change is equal to zero, then the free-energy change is equal to zero.
If the total entropy change is greater than zero, then the free-energy change of a system is less than zero.
If the temperature of a reaction having a negative total entropy change increases, then the free-energy change becomes more negative.
If the temperature of a reaction having a positive total entropy change increases, then the free-energy change becomes more negative.
If the total entropy change is less than zero, then the free-energy change is greater than zero.
Which combination of free-energy change and spontaneity is correctly matched for the reaction at 298 K
SO
3
(
g
) + H
2
O(
l
) ---> H
2
SO
4
(
aq
) under standard-state conditions? (enthalpies of formation: 90.2 kJ/mole (SO
3
(
g
)), -285.8 kJ (H
2
O(
l
)), and -909.3 kJ (H
2
SO
4
(
aq
)); entropies: 256.6 J/K (SO
3
(
g
)), 69.9 J/K (H
2
O(
l
)), and 20.0 J/K (H
2
SO
4
(
aq
))
-622.4 kJ : The forward reaction is spontaneous.
-622.4 kJ : The reverse reaction is spontaneous.
-706.0 kJ : The forward reaction is spontaneous.
630.2 kJ : The reverse reaction is nonspontaneous.
-630.2 kJ : The forward reaction is spontaneous.
Which statement is true concerning the reaction H
2
(
g
) + I
2
(
g
) ---> 2HI(
g
) under standard-state conditions? (enthalpy of formation : 26.5 kJ/mol (HI); entropies : 130.6 J/K (H
2
), 260.6 J/K (I
2
), 206.5 J/K (HI))
The forward reaction is spontaneous under standard-state conditions.
The forward reaction is nonspontaneous at all temperatures.
The forward reaction is endothermic.
The entropy change for the forward reaction has a negative value.
The reverse reaction is nonspontaneous under standard-state conditions.
Which statement is
not
true concerning the reaction H
+
(
aq
) + OH
-
(
aq
) ---> H
2
O(
l
) under standard-state conditions (298 K)? (enthalpies of formation : -285.8 kJ/mol (H
2
O), -230.0 kJ/mol (OH
-
(
aq
)); entropies : 69.9 J/mol·K (H
2
O(
l
)), -10.8 J/mol·K (OH
-
(
aq
))
If the concentrations of the ions are 1 M, the free-energy change for the reaction is -79.4 kJ.
The change in the free energy of this reaction assumes the reaction goes to completion.
The entropy of the system increases as the forward reaction occurs.
The reverse reaction is nonspontaneous at all temperatures.
The forward reaction becomes nonspontaneous at lower temperatures.
Which statement concerning compounds having positive free energies of formation is true?
Substances having positive free energies of formation will spontaneously decompose to their constituent elements.
Substances having positive free energies of formation can never be prepared.
Substances having large positive free energies will decompose faster.
Using a catalyst will favor the formation of a compound with a positive free energy of formation.
A more positive free energy of formation corresponds to a lesser stability of the substance with respect to all reactions in which it participates.
The standard free-energy change for the reaction CH
4
(
g
) + 4Cl
2
(
g
) ---> CCl
4
(
l
) + 4HCl(
g
) is (free energies of formation : -50.8 kJ/mol (CH
4
), -65.3 kJ/mol (CCl
4
), -95.3 kJ/mol (HCl))
396 kJ.
-396 kJ.
-109.8 kJ.
109.8 kJ.
-497 kJ.
Under which conditions will the reverse reaction of
C
2
H
5
OH(
g
) ---> C
2
H
4
(
g
) + H
2
O(
g
) be spontaneous? (standard free-energy change for the reaction = 8.1 kJ)
10.0 atm C
2
H
5
OH, 0.50 atm C
2
H
4
, and 0.10 atm H
2
O at 273 K
4.0 atm C
2
H
5
OH, 0.20 atm C
2
H
4
, and 0.20 atm H
2
O at 773 K
10.0 atm C
2
H
5
OH, 1.0 atm C
2
H
4
, and 1.0 atm H
2
O at 298 K
0.10 atm C
2
H
5
OH, 0.010 atm C
2
H
4
, and 1.0 atm H
2
O at 773 K
1.0 atm C
2
H
5
OH, 0.10 atm C
2
H
4
, and 0.10 atm H
2
O at 298 K
Which statement does
not
give the correct relationship between the standard free-energy change and the equilibrium constant?
If the standard free-energy change is less than zero, then ln K is greater than zero.
If K is greater than 1, then the standard free-energy change is less than zero.
If the standard free-energy change is less than zero, then K must be less than 1.
If ln K is less than zero, then the standard free-energy change is greater than zero.
If K equals 1, then the standard free-energy change is zero.
The standard free-energy change (in kJ) at 25 °C for the reaction
2A(
g
) + B(
g
)
2C(
g
) is (K
p
= 2.2 x 10
-2
)
-9.5 kJ.
9.5 kJ.
0.093 kJ.
-0.79 kJ.
0.79 kJ.
The vapor pressure of methanol at 25 °C is (standard free energies of formation : methanol(
l
) (-166.4 kJ/mole), methanol(
g
) (-161.9 kJ/mole))
1.0 atm.
6.1 atm.
4.0 x 10
-10
atm.
0.60 atm.
0.16 atm.
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