1062-2nd Chem Exam-1070516(A)
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) For a given reaction, S = +69.0 J/mol·K, and the reaction is spontaneous at temperatures above the crossover temperature, 439 K. The value of H = _______ kJ/mol, assuming that H and S do not vary with
temperature.
A) 30.3 B) 1.57 × 10-4 C) 6.36 × 10-3 D) -1.57 × 10-4 E) -30.3
Answer: A
2) A reversible process is one that ________.
A) is spontaneous in both directions B) must be carried out at low temperature
C) can be reversed with no net change in either system or surroundings D) happens spontaneously
E) must be carried out at high temperature Answer: C
3) A reaction that is not spontaneous at low temperature can become spontaneous at high temperature if H is ________ and S is ________.
A) +, + B) -, - C) +, - D) -, + E) +, 0
Answer: A
4) Consider a pure crystalline solid that is heated from absolute zero to a temperature above the boiling point of the liquid. Which of the following processes produces the greatest increase in the entropy of the substance?
A) heating the solid B) vaporizing the liquid C) melting the solid D) heating the liquid
E) heating the gas Answer: B
5) The standard Gibbs free energy of formation of ________ is zero.
(a) H2O (l) (b) Fe (s) (c) I2 (s) A) (a) only
B) (b) only C) (c) only D) (b) and (c)
E) (a), (b), and (c) Answer: D
6) Given the thermodynamic data in the table below, calculate the equilibrium constant (at 298 K) for the reaction:
2 SO2 (g) + O2 (g) 2 SO3 (g) Substance Hf° (kJ/mol) S° (J/mol · K)
SO2 (g) -297 249
O2 (g) 0 205
SO3 (g) -395 256
A) 1.06 B) 2.40 × 1024 C) 1.95 D) 3.82 × 1023
E) More data are needed.
Answer: B
7) The equilibrium constant for a reaction is 0.38 at 25 °C. What is the value of G° (kJ/mol) at this temperature?
A) 200 B) 4.2 C) -4.2 D) 2.4
E) More information is needed.
Answer: D
8) The second law of thermodynamics states that ________.
A) E = q + w
B) the entropy of a pure crystalline substance is zero at absolute zero C) S = qrev/T at constant temperature
D) for any spontaneous process, the entropy of the universe increases E) H°rxn = n H°f (products) - m H°f (reactants)
Answer: D 9) For the reaction
C2H6 (g) C2H4 (g) + H2 (g)
H° is +137 kJ/mol and S° is +120 J/K · mol. This reaction is ________.
A) spontaneous at all temperatures B) nonspontaneous at all temperatures C) spontaneous only at high temperature D) spontaneous only at low temperature Answer: C
10) The normal boiling point of methanol is 64.7 °C and the molar enthalpy of vaporization if 71.8 kJ/mol. The value of S when 1.75 mol of CH3OH (l) vaporizes at 64.7 °C is ________ J/K.
A) 372 B) 4.24 × 107 C) 1.94 D) 0.372 E) 1.94 × 103
Answer: A
Use the table below to answer the questions that follow.
Thermodynamic Quantities for Selected Substances at 298.15 K (25 °C) Substance H°f (kJ/mol) G°f (kJ/mol) S (J/K-mol)
Carbon
C (s, diamond) 1.88 2.84 2.43
C (s, graphite) 0 0 5.69
C2H2 (g) 226.7 209.2 200.8
C2H4 (g) 52.30 68.11 219.4
C2H6 (g) -84.68 -32.89 229.5
CO (g) -110.5 -137.2 197.9
CO2 (g) -393.5 -394.4 213.6
Hydrogen
H2( g) 0 0 130.58
Oxygen
O2 (g) 0 0 205.0
H2O (l) -285.83 -237.13 69.91
11) The value of S° for the catalytic hydrogenation of acetylene to ethene, C2H2 (g) + H2 (g) C2H4 (g)
is ________ J/K· mol.
A) +112.0 B) -18.6 C) -112.0 D) +550.8 E) +18.6
Answer: C
12) With thermodynamics, one cannot determine ________.
A) the extent of a reaction
B) the temperature at which a reaction will be spontaneous C) the speed of a reaction
D) the direction of a spontaneous reaction E) the value of the equilibrium constant Answer: C
13) Of the following, the entropy of gaseous ________ is the largest at 25 °C and 1 atm.
A) Cl2 B) O3 C) F2 D) I2 E) Br2
Answer: D
14) A solution containing which one of the following pairs of substances will be a buffer solution?
A) KBr, HBr B) NaI, HI C) CsF, HF D) RbCl, HCl
E) none of the above
15) A solution is prepared by dissolving 0.23 mol of hydrofluoric acid and 0.27 mol of sodium fluoride in water sufficient to yield 1.00 L of solution. The addition of 0.05 mol of HCl to this buffer solution causes the pH to drop slightly. The pH does not decrease drastically because the HCl reacts with the __________ present in the buffer solution. The Ka of hydrofluoric acid is 1.36 × 10-3.
A) fluoride ion B) H3O+
C) hydrofluoric acid D) H2O
E) This is a buffer solution: the pH does not change upon addition of acid or base.
Answer: A
16) Which of the following could be added to a solution of sodium acetate to produce a buffer?
A) acetic acid or hydrochloric acid B) sodium chloride or potassium acetate C) potassium acetate only
D) acetic acid only E) hydrochloric acid only Answer: A
17) Of the following solutions, which has the greatest buffering capacity?
A) They are all buffer solutions and would all have the same capacity.
B) 0.821 M HF and 0.217 M NaF C) 0.100 M HF and 0.217 M NaF D) 0.821 M HF and 0.909 M NaF E) 0.121 M HF and 0.667 M NaF Answer: D
18) In which of the following aqueous solutions would you expect PbCl2to have the lowest solubility?
A) 0.015 M PbNO3 B) 0.015 M NaCl C) 0.020 M KCl D) pure water
E) 0.020 M BaCl2 Answer: E
19) A result of the common-ion effect is __________.
A) that ions such as K+ and Na+ are common ions, so that their values in equilibrium constant expressions are always 1.00
B) that common ions, such as Na+ (aq), don't affect equilibrium constants
C) that some ions, such as Na+ (aq), frequently appear in solutions but do not participate in solubility equilibria
D) that the selective precipitation of a metal ion, such as Ag+, is promoted by the addition of an appropriate counterion (X-) that produces a compound (AgX) with a very low solubility
E) that common ions precipitate all counter-ions Answer: D
20) What is the solubility (in M) of PbCl2 in a 0.15 M solution of HCl? The Ksp of PbCl2 is 1.6 × 10-5.
A) 7.1 × 10-4 B) 1.1 × 10-4 C) 2.0 × 10-3 D) 1.8 × 10-4 E) 1.6 × 10-5 Answer: A
21) Calculate the pH of a solution prepared by dissolving 0.150 mol of benzoic acid and 0.300 mol of sodium benzoate in water sufficient to yield 1.00 L of solution. The Ka of benzoic acid is 6.30 × 10-5.
A) 4.195 B) 2.516 C) 4.502 D) 10.158 E) 3.892
Answer: C
22) A 25.0 mL sample of an HCl solution is titrated with a 0.139 M NaOH solution. The equivalence point is reached with 25.3 mL of base. The concentration of HCl is __________ M.
A) 0.0352 B) 11.7 C) 0.00352 D) 0.139 E) 0.141
Answer: E
23) A 25.0 mL sample of 0.723 M HClO4 is titrated with a 0.27 M KOH solution. The H3O+ concentration after the addition of 80.0 mL of KOH is __________ M.
A) 4 × 10-2 B) 0.7 C) 1 × 10-7 D) 0.4 E) 3 × 10-13
Answer: E
24) A 25.0 mL sample of a solution of an unknown compound is titrated with a 0.115 M NaOH solution. The titration curve above was obtained. The unknown compound is __________.
A) a weak base B) a strong acid C) a strong base D) a weak acid
E) neither an acid nor a base Answer: D
25) The solubility of manganese (II) hydroxide (Mn(OH)2) is 2.2 × 10-5 M. What is the Ksp of Mn(OH)2?
A) 2.1 × 10-14 B) 1.1 × 10-14 C) 2.2 × 10-5 D) 4.8 × 10-10 E) 4.3 × 10-14 Answer: E
26) Calculate the maximum concentration (in M) of silver ions (Ag+) in a solution that contains 0.025 M of CO32-.
The Ksp of Ag2CO3 is 8.1 × 10-12.
A) 1.4 × 10-6 B) 8.1 × 10-12 C) 2.8 × 10-6 D) 1.8 × 10-5 E) 3.2 × 10-10 Answer: D
27) A solution of NaF is added dropwise to a solution that is 0.0144 M in Ba2+. When the concentration of F- exceeds __________ M, BaF2 will precipitate. Neglect volume changes. For BaF2, Ksp = 1.7 × 10-6.
A) 2.7 × 10-3 B) 5.9 × 10-5 C) 1.1 × 10-2 D) 1.2 × 10-4 E) 2.4 × 10-8 Answer: C
28) Which one of the following is a Br nsted-Lowry acid?
A) HNO2 B) (CH3)3NH+
C) HF
D) CH3COOH E) all of the above Answer: E
29) Which one of the following statements regarding Kw is false?
A) Kw changes with temperature.
B) Kw is known as the ion product of water.
C) The value of Kw shows that water is a weak acid.
D) pKw is 14.00 at 25°C
E) The value of Kw is always 1.0 × 10-14.
Answer: E
30) Classify the following compounds as weak acids (W) or strong acids (S):
hydrocyanic acid hydrofluoric acid phenol
A) W W W B) S W W C) W S W D) W S S E) S S S
Answer: A
31) HA is a weak acid. Which equilibrium corresponds to the equilibrium constant Kb for A-?
A) A- (aq) + H2O (l) HA (aq) + OH- (aq) B) HA (aq) + H2O (l) H2A+ (aq) + OH- (aq) C) A- (aq) + H3O+ (aq) HA (aq) + H2O (l) D) A- (aq) + OH- (aq) HOA2- (aq)
E) HA (aq) + OH- (aq) H2O (l) + H+ (aq) Answer: A
32) In which of the following aqueous solutions does the weak acid exhibit the lowest percentage ionization?
A) 0.01 M HC2H3O2 (Ka = 1.8 × 10-5) B) 0.01 M HF (Ka = 6.8 × 10-4) C) 0.01 M HClO (Ka = 3.0 × 10-8) D) 0.01 M HNO2 (Ka = 4.5 × 10-4)
E) These will all exhibit the same percentage ionization.
Answer: C
33) Using the data in the table, which of the conjugate bases below is the weakest base?
Acid Ka
HOAc 1.8 × 10-5 HC7H5O2 6.3 × 10-5 HNO2 4.5 × 10-4
HF 6.8 × 10-4
A) C7H5O2- B) F- C) NO2- D) OAc-
E) OAc- and C7H5O2- Answer: B
34) Which of the following aqueous solutions has the lowest [OH-]?
A) a 1 × 10-3 M solution of NH4Cl B) a 1 × 10-4 M solution of HNO3 C) pure water
D) a solution with a pOH of 12.0 E) a solution with a pH of 3.0 Answer: D
35) Of the following substances, an aqueous solution of __________ will form basic solutions.
NH4Cl Cu(NO3)2 K2CO3 NaF A) NaF only
B) K2CO3, NH4Cl C) NaF, K2CO3 D) NH4Cl, Cu(NO3)2
E) NH4Cl only Answer: C
36) What is the pH of an aqueous solution at 25.0 °C that contains 3.98 × 10-9 M hydroxide ion?
A) 9.00 B) 3.98 C) 8.40 D) 5.60 E) 7.00
Answer: D
37) The Ka for formic acid (HCO2H) is 1.8 × 10-4. What is the pH of a 0.10 M aqueous solution of sodium formate (NaHCO2)?
A) 3.39 B) 5.63 C) 4.26 D) 11.64 E) 8.37
Answer: E
38) The pH of a 0.55 M aqueous solution of hypobromous acid, HBrO, at 25.0 °C is 4.48. What is the value of Ka for HBrO?
A) 3.3 × 10-5 B) 2.0 × 10-9 C) 6.0 × 10-5 D) 1.1 × 10-9 E) 3.0 × 104 Answer: B
39) A 7.0 × 10-3 M aqueous solution of Ca(OH)2 at 25.0 °C has a pH of __________.
A) 11.85 B) 12.15 C) 7.1 × 10-13 D) 1.85 E) 1.4 × 10-2
Answer: B
40) The base-dissociation constant of ethylamine (C2H5NH2) is 6.4 × 10-4 at 25.0 °C. The [H+] in a 1.6 × 10-2 M solution of ethylamine is __________ M.
A) 3.2 × 10-3 B) 3.5 × 10-12 C) 11.46 D) 3.1 × 10-12 E) 2.9 × 10-3 Answer: D
