62) 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
63) 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.
64) 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)
65) When equilibrium is reached at constant temperature and pressure,
A) Q = 1.
B) ΔG° = 0.
C) S is maximized.
D) G is minimized.
66) 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
67) 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 ΔG° for this process.
A) 832 kJ
B) 799 kJ
C) 281 kJ
D) 247 kJ
68) 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
69) If ΔG° is negative for a reaction,
A) K < 0.
B) K = 0.
C) K is between 0 and 1.
D) K > 1.
70) If ΔG° is positive for a reaction,
A) K < 0.
B) K = 0.
C) K is between 0 and 1.
D) K > 1.
71) 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.
72) 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.
73) Which of the following must be true in order for this reaction to always proceed spontaneously?
A) K = Q
B) K > Q
C) K < Q
D) None of these, spontaneity is dependent on reaction conditions.
74) 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 = –
75) 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 = –
76) 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 = –
26
77) 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 = –
78) 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 = –
79) 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 = –
80) 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.
81) 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 = –
82) 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.
Consider the reaction 2A(g) ⇌ A2(g). The following pictures represent two possible initial states and the
equilibrium state of the system.
83) For initial state 1 what is the relationship between the reaction quotient, Qp, and the equilibrium
constant, Kp?
A) Qp < Kp
B) Qp = Kp = 1
C) Qp = Kp ≠ 1
D) Qp > Kp
84) For initial state 2 what is the relationship between the reaction quotient, Qp, and the equilibrium
constant, Kp?
A) Qp < Kp
B) Qp = Kp = 1
C) Qp = Kp ≠ 1
D) Qp > Kp
85) What are the signs (+ or –) of ΔH, ΔS, and ΔG when the system spontaneously goes from initial state 1
to the equilibrium state?
A) ΔH = +, ΔS = +, ΔG = +
B) ΔH = +, ΔS = +, ΔG = –
C) ΔH = –, ΔS = –, ΔG = +
D) ΔH = –, ΔS = –, ΔG = –
86) What are the signs (+ or –) of ΔH, ΔS, and ΔG when the system spontaneously goes from initial state 2
to the equilibrium state?
A) ΔH = +, ΔS = +, ΔG = +
B) ΔH = +, ΔS = +, ΔG = –
C) ΔH = –, ΔS = –, ΔG = +
D) ΔH = –, ΔS = –, ΔG = –
Consider the following gas-phase reaction of A2 (shaded spheres) and B2 (unshaded spheres):
A2(g) + B2(g) ⇌ 2 AB(g) ΔG ° = +25 kJ
87) Which of the above reaction mixtures has the least spontaneous forward reaction?
A) (1)
B) (2)
C) (3)
D) (4)
88) Which of the above reaction mixtures has the most spontaneous forward reaction?
A) (1)
B) (2)
C) (3)
D) (4)
89) Which of the above reaction mixtures is ΔG of reaction = ΔG °?
A) (1)
B) (2)
C) (3)
D) (4)
90) According to the diagram above, the forward reaction is
A) nonspontaneous at d and e, and spontaneous at f.
B) nonspontaneous at d, at equilibrium at e, and spontaneous at f.
C) spontaneous at d, at equilibrium at e, and nonspontaneous at f.
D) spontaneous at d, e, and f.
91) According to the diagram above,
A) ΔG° is positive and the equilibrium composition is rich in products.
B) ΔG° is positive and the equilibrium composition is rich in reactants.
C) ΔG° is negative and the equilibrium composition is rich in products.
D) ΔG° is negative and the equilibrium composition is rich is reactants.
92) According to the diagram above,
A) ΔG° is positive and is equal to a – b.
B) ΔG° is positive and is equal to b – c.
C) ΔG° is negative and is equal to b – c.
D) ΔG° is negative and is equal to a – c.
93) The following pictures represent three equilibrium mixtures for the interconversion of A, B, and C
molecules (unshaded spheres) into X, Y, and Z molecules (shaded spheres), respectively. What is the sign
of ΔG ° for each of the three reactions?
A) ΔG °(1) = –; ΔG °(2) = +; ΔG °(3) = 0
B) ΔG °(1) = –; ΔG °(2) = 0; ΔG °(3) = +
C) ΔG °(1) = 0; ΔG °(2) = –; ΔG °(3) = +
D) ΔG °(1) = +; ΔG °(2) = 0; ΔG °(3) = –
17.2 Algorithmic Questions
1) The chemical system shown below is at equilibrium. Which change in conditions will not result in a
spontaneous forward reaction?
N2(g) + 3 H2(g) ⇌ 2 NH3(g) Kp = 4 × 105
A) adding a catalyst
B) adding more N2
C) decreasing the NH3
D) increasing the pressure
2) Which of the following processes is spontaneous?
A) a mixture of two liquids separating into pure compounds
B) reaction of sodium with oxygen
C) precipitation of solute from a unsaturated solution
D) water flowing uphill
3) For which of the following will the entropy of the system increase?
A) condensation of steam
B) reaction of zinc with oxygen to form zinc oxide
C) reaction of nitrogen and hydrogen to form ammonia
D) sublimation of dry ice