67) Which is the lowest at 25°C?
A) ΔG°f for H2O (s)
B) ΔG°f for H2O (l)
C) ΔG°f for H2O (g)
D) 1/2ΔG°f for O2 (g) plus ΔG°f for H2O (g)
68) Which of the following is zero at 25°C?
A) ΔG°f for N2(g)
B) ΔG°f for H2O (l)
C) S° for N2 (g)
D) S° for H2O (l)
69) A positive value of ΔG°f for a solid compound at 25°C means the
A) compound cannot exist at 25°C and 1 atm.
B) compound must be a liquid or a gas at 25°C and 1 atm.
C) process of forming the compound from the elements is exothermic.
D) process of forming the compound from the stable elements at 25°C and 1 atm is
nonspontaneous.
70) At 25°C, ΔG°f is -620 kJ/mol for SiCl4(g) and -592 kJ/mol for MgCl2(s). Calculate ΔG° for
the reaction, and determine if the reaction is spontaneous at
25°C if the pressure of SiCl4(g) is 1 atm.
A) ΔG° = 28 kJ; the process is spontaneous.
B) ΔG° = 28 kJ; the process is nonspontaneous.
C) ΔG° = -564 kJ; the process is spontaneous.
D) ΔG° = -564 kJ; the process is nonspontaneous.
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71) Which of the following are unstable with respect to their constituent elements at 25°C?
A) C8H18(l), CH3OH(l)
B) C8H18(l), C2H2(g)
C) C2H2(g)
D) CH3OH(l)
72) In general, as a reaction goes to equilibrium
A) ΔG decreases.
B) ΔG°f decreases.
C) ΔG goes to zero.
D) ΔG° decreases.
73) At 25°C, ΔG° = -198 kJ for the reaction, NO(g) + O3(g) ⇌ NO2(g) + O2(g).
Calculate ΔG under the following conditions:
A) -159 kJ
B) -167 kJ
C) -198 kJ
D) -236 kJ
74) For a reaction at constant temperature, as Q increases
A) ΔG and ΔG° increase.
B) ΔG and ΔG° decrease.
C) ΔG increases, but ΔG° remains constant.
D) ΔG decreases, but ΔG° remains constant.
75) At high temperatures boron carbide vaporizes according to the equation
B4C(s) ⇌ 4 B(g) + C(s)
Which equation describes the relationship between ΔG° and ΔG for this reaction?
A) ΔG = ΔG° + R T ln (pB ∙ [C]/[B4C])
B) ΔG = ΔG° + R T ln pB
C) ΔG = ΔG° + 4 R T ln pB
D) ΔG = ΔG° – 4 R T ln pB
76) At 2600 K, ΔG° = 775 kJ for the vaporization of boron carbide:
B4C(s) ⇌ 4 B(g) + C(s)
Find ΔG and determine if the process is spontaneous if the reaction vessel contains 4.00 mol
B4C(s), 0.400 mol of C(s), and B(g) at a partial pressure of 1.0 × 10-5 atm. At this temperature,
R T = 21.6 kJ.
A) ΔG = -270 kJ; spontaneous.
B) ΔG = -270 kJ; nonspontaneous.
C) ΔG = -220 kJ; spontaneous.
D) ΔG = -220 kJ; nonspontaneous.
77) ΔG = ΔG° for a reaction
A) if Q = K.
B) if Q = 1.
C) at STP.
D) at the start of the reaction.
78) What is the relationship between ΔG and the ΔG°F for the reaction below?
MgF2(s) → Mg2+(aq) + 2 F–(aq)
A) ΔG = {ΔG°f [Mg2+ (aq)] + 2 ΔG°f [F– (aq)] – ΔG°f [MgF2 (s)]} + RT ln ([Mg2+]
[F–]2/[MgF2])
B) ΔG = {ΔG°f [Mg2+ (aq)] + 2 ΔG°f [F– (aq)] – ΔG°f [MgF2 (s)]} + RT ln ([Mg2+] [F–])2)
C) ΔG = {ΔG°f [Mg2+ (aq)] + 2 ΔG°f [F– (aq)]} + RT ln ([Mg2+] [F–]2)
D) ΔG = {ΔG°f [Mg2+ (aq)] + 2 ΔG°f [F– (aq)] – ΔG°f [MgF2 (s)]} + RT ln Ksp
79) If Q increases
A) ΔG increases and the reaction becomes more spontaneous.
B) ΔG increases and the reaction becomes less spontaneous.
C) ΔG decreases and the reaction becomes more spontaneous.
D) ΔG decreases and the reaction becomes less spontaneous.
80) What is the relationship between ΔG, Qp, and Kp for a reaction involving gases?
A) ΔG = Qp/Kp
B) ΔG = Kp/Qp
C) ΔG = RTln(Qp/Kp)
D) ΔG = RTln(Kp/Qp)
81) When equilibrium is reached at constant temperature and pressure,
A) Q = 1.
B) ΔG° = 0.
C) S is maximized.
D) G is minimized.
82) Calculate Ksp for PbI2 at 25°C based on the following data:
A) 4 × 10-31
B) 8 × 10-18
C) 9 × 10-9
D) 5 × 10-5
83) At high temperatures, boron carbide vaporizes according to
B4C(s) ⇌ 4 B(g) + C(s)
At 2500 K, the equilibrium pressure of B(g) is 0.0342 mm Hg over a mixture of 0.300 mol
B4C(s) and 0.500 mol C(s). Calculate for this process.
A) 832 kJ
B) 799 kJ
C) 281 kJ
D) 247 kJ
84) Solid NaHCO3 is heated to 90°C. At equilibrium the total pressure of the gases produced is
0.545 atm. Calculate ΔG° at 90°C for the reaction
2 NaHCO3(s) ⇌ Na2CO3(s) + H2O(g) + CO2(g).
A) -7.85 kJ
B) -3.67 kJ
C) +3.67 kJ
D) +7.85 kJ
85) What is K if ΔG° = -18.0 kJ for a reaction at 25°?
A) 1.4 × 103
B) 1.2 × 102
C) 8.1 × 10-3
D) 7.3 × 10-4
86) If ΔG° is negative for a reaction,
A) K < 0.
B) K = 0.
C) K is between 0 and 1.
D) K > 1.
87) If ΔG° is positive for a reaction,
A) K < 0.
B) K = 0.
C) K is between 0 and 1.
D) K > 1.
88) For the following reaction find Kp at 25°C and indicate whether Kp should increase or
decrease as the temperature rises.
NH4HS(s) ⇌ H2S(g) + NH3(g) ΔH° = 83.47 kJ and ΔG° = 17.5 kJ at 25°C.
A) Kp = 8.6 × 10-4 and Kp should increase as the temperature rises.
B) Kp = 8.6 × 10-4 and Kp should decrease as the temperature rises.
C) Kp = 1.2 × 103 and Kp should increase as the temperature rises.
D) Kp = 1.2 × 103 and Kp should decrease as the temperature rises.
89) If ΔG is small and positive,
A) the forward reaction is spontaneous and the system is far from equilibrium.
B) the forward reaction is spontaneous and the system is near equilibrium.
C) the reverse reaction is spontaneous and the system is far from equilibrium.
D) the reverse reaction is spontaneous and the system is near equilibrium.
90) In figure (1) below argon atoms, represented by unshaded spheres, and neon atoms,
represented by shaded spheres, are in separate compartments. Figure (2) shows the equilibrium
state of the system after the stopcock separating the two compartments is opened. Assuming that
argon and neon behave as ideal gases, what are the signs (+, –, or 0) of ΔH, ΔS, and ΔG for this
process?
A) ΔH = +, ΔS = –, ΔG = +
B) ΔH = 0, ΔS = +, ΔG = –
C) ΔH = 0, ΔS = –, ΔG = +
D) ΔH = –, ΔS = +, ΔG = –
91) In figure (1) below oxygen molecules, represented by unshaded spheres, and chlorine
molecules, represented by shaded spheres, are in separate compartments. Figure (2) shows the
equilibrium state of the system after the stopcock separating the two compartments is opened.
Assuming the oxygen and the chlorine behave as ideal gases, what are the signs (+, -, or 0) of
ΔH, ΔS, and ΔG for this process?
A) ΔH = +, ΔS = –, ΔG = +
B) ΔH = 0, ΔS = +, ΔG = –
C) ΔH = 0, ΔS = –, ΔG = +
D) ΔH = –, ΔS = +, ΔG = –
92) The figure represents the spontaneous deposition of iodine in which iodine vapor, I2(g),
becomes crystalline iodine solid I2(s): I2(g): → I2(s). What are the signs (+ or –) of ΔH, ΔS, and
ΔG for this process?
A) ΔH = +, ΔS = +, ΔG = +
B) ΔH = +, ΔS = +, ΔG = –
C) ΔH = –, ΔS = –, ΔG = +
D) ΔH = –, ΔS = –, ΔG = –
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93) The figure represents the spontaneous evaporation of nitrogen in which liquid nitrogen,
N2(l), becomes gaseous nitrogen, N2(g): N2(l) → N2(g). What are the signs (+ or –) of ΔH, ΔS,
and ΔG for this process?
A) ΔH = +, ΔS = +, ΔG = +
B) ΔH = +, ΔS = +, ΔG = –
C) ΔH = –, ΔS = –, ΔG = +
D) ΔH = –, ΔS = –, ΔG = –
94) An ideal gas is expanded at constant temperature. What are the signs (+, –, or 0) of ΔH, ΔS,
and ΔG for this system?
A) ΔH = +, ΔS = –, ΔG = +
B) ΔH = 0, ΔS = +, ΔG = –
C) ΔH = 0, ΔS = –, ΔG = +
D) ΔH = –, ΔS = +, ΔG = –
95) The figure above represents the nonspontaneous reaction O2(g) → 2O(g). What are the signs
(+ or –) of ΔH, ΔS, and ΔG for this process?
A) ΔH = +, ΔS = +, ΔG = +
B) ΔH = +, ΔS = +, ΔG = –
C) ΔH = –, ΔS = –, ΔG = +
D) ΔH = –, ΔS = –, ΔG = –
96) The figure above represents the reaction O2(g) → 2O(g), which is nonspontaneous at 25°C.
How will the spontaneity of this reaction vary with temperature? This reaction is
A) nonspontaneous at all temperatures.
B) nonspontaneous at high temperatures and spontaneous at low temperatures.
C) spontaneous at high temperatures and nonspontaneous at low temperatures.
D) spontaneous at all temperatures.
The figure below represents the spontaneous reaction of H2 (shaded spheres) with O2 (unshaded
spheres) to produce gaseous H2O.
97) What are the signs (+, or –) of ΔH, ΔS, and ΔG for this process?
A) ΔH = +, ΔS = +, ΔG = +
B) ΔH = +, ΔS = +, ΔG = –
C) ΔH = –, ΔS = –, ΔG = +
D) ΔH = –, ΔS = –,ΔG = –
98) How will the spontaneity of this reaction vary with temperature? This reaction is
A) nonspontaneous at all temperatures.
B) nonspontaneous at high temperatures and spontaneous at low temperatures.
C) spontaneous at high temperatures and nonspontaneous at low temperatures.
D) spontaneous at all temperatures.