21
63) Which of the following is not true?
A) A spontaneous reaction need not occur immediately.
B) A spontaneous reaction must be exothermic and must have an increase in entropy.
C) The reverse of a nonspontaneous reaction is always spontaneous.
D) A spontaneous reaction is one that can proceed on its own.
64) Determine the sign of ΔS° for each of the following:
I. The mixing of two gases at a given temperature and pressure
II. C(s) + 2 H2O(g) → CO2(g) + 2 H2(g)
A) ΔS° is negative for I and negative for II.
B) ΔS° is negative for I and positive for II.
C) ΔS° is positive for I and negative for II.
D) ΔS° is positive for I and positive for II.
65) Which combination always results in a reaction being spontaneous?
A) ΔH is negative and ΔS is negative.
B) ΔH is negative and ΔS is positive.
C) ΔH is positive and ΔS is negative.
D) ΔH is positive and ΔS is positive.
66) The reaction 4 Ag(s) + O2(g) → 2 Ag2O(s) favors Ag2O at low temperature, but it favors Ag and O2 at
high temperatures. How can this be explained in terms of ΔH and ΔS?
A) ΔH is negative and ΔS is negative.
B) ΔH is negative and ΔS is positive.
C) ΔH is positive and ΔS is negative.
D) ΔH is positive and ΔS is positive.
67) What is the thermodynamic criterion for equilibrium for a reaction at constant temperature and
pressure (PV work only)?
A) ΔS = 0
B) ΔG = 0
C) ΔS > 0
D) ΔG < 0
68) If an endothermic reaction is spontaneous at constant temperature and pressure,
A) ΔG is negative and ΔS may be positive or negative.
B) ΔG is negative and ΔS is positive.
C) ΔG is positive and ΔS is negative.
D) ΔG is positive and ΔS may be positive or negative.
69) If a reaction with a negative value of ΔS is nonspontaneous at constant temperature and pressure,
A) ΔG is negative and ΔH may be positive or negative.
B) ΔG is negative and ΔH is positive.
C) ΔG is positive and ΔH may be positive or negative.
D) ΔG is positive and ΔH is positive.
70) Consider the conversion of white tin to gray tin:
Sn(white) → Sn(gray) ΔH° = -2.09 kJ ΔS° = -7.41 J/K
Based on these data,
A) white tin is stable below 9°C and gray tin is stable above 9°C.
B) gray tin is stable below 9°C and white tin is stable above 9°C.
C) white tin is stable below 15°C and gray tin is stable above 15°C.
D) gray tin is stable below 15°C and white tin is stable above 15°C.
71) When heated, mercury(II) oxide decomposes into elemental mercury and oxygen:
2 HgO(s) → 2 Hg(l) + O2(g) ΔH° = 181.6 kJ ΔS° = 216.4 J/K
Estimate the temperature at which HgO should begin to decompose if the partial pressure of O2(g) is
constant at 1.00 atm.
A) -34.8°C
B) 34.8°C
C) 566°C
D) 840°C
72) Methanol can be produced from carbon monoxide and hydrogen with suitable catalysts:
CO(g) + 2 H2(g) → CH3OH(l) at 25°C ΔH° = –128.1 kJ and ΔS° = –332 J/K
Find ΔG° at 25°C.
A) -157.2 kJ
B) -29.1 kJ
C) 98.9 kJ
D) 157.2 kJ
73) For the conversion of water to ice at 25°C and 1 atm,
A) ΔG is negative and ΔH is negative.
B) ΔG is negative and ΔH is positive.
C) ΔG is positive and ΔH is negative.
D) ΔG is positive and ΔH is positive.
74) Calculate ΔG° for the reaction below and tell whether it is spontaneous or nonspontaneous under
standard conditions at 25°C.
2 S (s) + 3 O2 (g) + 2 H2O (l) → 2 H2SO4 (l) ΔH° = -1056 kJ/mol
ΔS° = –505 J/mol
A) ΔG° = -1207 kJ and the process is spontaneous.
B) ΔG° = -1207 kJ and the process is nonspontaneous.
C) ΔG° = -906 kJ and the process is spontaneous.
D) ΔG° = -906 kJ and the process is nonspontaneous.
75) The enthalpy of fusion of naphthalene, C10H8, is 19.1 kJ/mol at 78.2°C, its melting point. Calculate the
entropy of fusion at the melting point.
A) ΔS°fus = 244 J/(K ∙ mol)
B) ΔS°fus = 54.4 J/(K ∙ mol)
C) ΔS°fus = 1.49 J/(K ∙ mol)
D) ΔS°fus = –1.49 J/(K ∙ mol)
76) Imagine a reaction that results in a change in both volume and temperature, as shown in the diagram
below. What is the sign of the work being done and the sign of the enthalpy change involved in this
reaction?
A) w = + and ΔH = +
B) w = + and ΔH = –
C) w = – and ΔH = +
D) w = – and ΔH = –
77) Imagine a reaction that results in a change in both volume and temperature, as shown in the diagram
below. What is the sign of the work being done, and what is the sign of the enthalpy change involved in
this reaction?
A) w = + and ΔH = +
B) w = + and ΔH = –
C) w = – and ΔH = +
D) w = – and ΔH = –
78) Imagine a reaction that results in a change in both volume and temperature, as shown in the diagram
below. What is the sign of the work being done and the sign of the enthalpy change involved in this
reaction?
A) w = + and ΔH = +
B) w = + and ΔH = –
C) w = – and ΔH = +
D) w = – and ΔH = –
79) Imagine a reaction that results in a change in both volume and temperature, as shown in the diagram
below. What is the sign of the work being done, and what is the sign of the enthalpy change involved in
this reaction?
A) w = + and ΔH = +
B) w = + and ΔH = –
C) w = – and ΔH = +
D) w = – and ΔH = –
27
80) Step (1) in the reaction is represented by
A) arrow A.
B) arrow B.
C) arrow C.
D) line E.
81) Step (2) in the reaction is represented by
A) arrow A.
B) arrow B.
C) arrow C.
D) line E.
82) The net reaction is represented by
A) arrow A.
B) arrow B.
C) arrow C.
D) line F.
83) The reactants, R + 2 S, are represented by
28
A) arrow B.
B) line D.
C) line E.
D) line F.
84) The product, Z, is represented by
A) arrow A.
B) line D.
C) line E.
D) line F.
85) The intermediate, T, + S is represented by
A) arrow C.
B) line D.
C) line E.
D) line F.
86) What are the signs of ΔH, ΔS, and ΔG for the following spontaneous change?
A) ΔH = +, ΔS = +, ΔG = –
B) ΔH = +, ΔS = –, ΔG = –
C) ΔH = –, ΔS = +, ΔG = –
D) ΔH = –, ΔS = –, ΔG = –
87) What are the signs of ΔH, ΔS, and ΔG for the following spontaneous change?
A) ΔH = +, ΔS = +, ΔG = –
B) ΔH = +, ΔS = –, ΔG = –
C) ΔH = –, ΔS = +, ΔG = –
D) ΔH = –, ΔS = –, ΔG = –
88) What are the signs of ΔH, ΔS, and ΔG for the following spontaneous change?
A) ΔH = +, ΔS = +, ΔG = –
B) ΔH = +, ΔS = –, ΔG = –
C) ΔH = –, ΔS = +, ΔG = –
D) ΔH = –, ΔS = –, ΔG = –
89) What are the signs of ΔH and ΔS for the reaction represented in the above drawing?
A) ΔH = +, ΔS = +
B) ΔH = +, ΔS = –
C) ΔH = –, ΔS = +
D) ΔH = –, ΔS = –
90) The reaction represented in the above drawing is likely to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and non spontaneous at high temperatures.
D) spontaneous at all temperatures.
91) What are the signs of ΔH and ΔS for the reaction represented in the above drawing?
A) ΔH = +, ΔS = +
B) ΔH = +, ΔS = –
C) ΔH = –, ΔS = +
D) ΔH = –, ΔS = –
92) The reaction represented in the above drawing is likely to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and non spontaneous at high temperatures.
D) spontaneous at all temperatures.
93) What are the signs of ΔH and ΔS for this reaction?
A) ΔH = +, ΔS = +
B) ΔH = +, ΔS = –
C) ΔH = –, ΔS = +
D) ΔH = –, ΔS = –
94) This reaction is likely to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and nonspontaneous at high temperatures.
D) spontaneous at all temperatures.
95) The following drawing is a representation of a reaction of the type A → B, where different shaded
spheres represent different molecular structures. For this reaction ΔH° = +45 kJ. This reaction is likely to
be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and nonspontaneous at high temperatures.
D) spontaneous at all temperatures.
96) The following drawing is a representation of a reaction of the type A → B, where different shaded
spheres represent different molecular structures. For this reaction ΔH° = -30 kJ. This reaction is likely to
be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and nonspontaneous at high temperatures.
D) spontaneous at all temperatures.
97) The following drawing is a representation of a reaction for which ΔH° = +62 kJ. This reaction is likely
to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and nonspontaneous at high temperatures.
D) spontaneous at all temperatures.
98) The following drawing is a representation of a reaction for which ΔH° = -22 kJ. This reaction is likely
to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and nonspontaneous at high temperatures.
D) spontaneous at all temperatures.
9.2 Algorithmic Questions
1) For a process at constant pressure, 24,800 calories of heat are released. This quantity of heat is
equivalent to
A) 9.64 × 10-6 J.
B) 5.92 × 103 J.
C) 2.48 × 104 J.
D) 1.04 × 105 J.
2) At 298 K the average kinetic energy is the same for H2, He, and N2. The gas with the highest average
velocity is
A) H2.
B) Kr.
C) Cl2.
D) All have the same average velocity.
3) The energy of motion is
A) electrical energy.
B) dam energy.
C) reserve energy.
D) kinetic energy.
4) For a system at constant pressure, 19,400 calories of heat are released. This quantity of heat is
equivalent to
A) 6.92 × 10-5 J.
B) 8.12 × 103 J.
C) 1.94 × 104 J.
D) 8.12 × 104 J.
5) A slice of cheese pizza has a caloric content of 550 Cal. If this energy could be used to power a 2500
Watt microwave oven, how many minutes could the microwave oven be operated? 1 W = 1 J/s
A) 917 min
B) 15.3 min
C) 3.00 min
D) 15 min
6) Which of the following is not a type of energy or energy transfer?
A) thermal energy
B) heat
C) height
D) work
7) Which of the following is not a state function?
A) depth
B) heat
C) internal energy
D) gas
8) The first law of thermodynamics
A) defines water energy.
B) defines energy.
C) is a statement of conservation of energy.
D) provides a criterion for the spontaneity of a reaction.
9) Calculate the work, w, gained or lost by the system when a gas expands from 15 L to 35 L against a
constant external pressure of 1.5 atm. 1 L ∙ atm = 101 J
A) -5.3 kJ
B) -3.0 kJ
C) +3.0 kJ
D) +5.3 kJ
10) For a particular process that is carried out at constant pressure, q = 140 kJ and w = -30 kJ. Therefore,
A) ΔE = 110 kJ and ΔH = 140 kJ.
B) ΔE = 140 kJ and ΔH = 110 kJ.
C) ΔE = 140 kJ and ΔH = 170 kJ.
D) ΔE = 170 kJ and ΔH = 140 kJ.
11) At constant pressure for which of the reactions shown below should ΔH° be greater than ΔE°?
I. 2 SO2(g) + O2(g) → 2 SO3(g)
II. C9H20(g) + 14 O2(g) → 9 CO2(g) + 10 H2O(l)
III. H2(g) + F2(g) → 2 HF(g)
IV. N2O4(g) → 2 NO2(g)
A) I
B) III
C) IV
D) II and IV