Exam Name MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 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 C2H4 (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 1) The combustion of acetylene in the presence of excess oxygen yields carbon dioxide and water: 1) 2C2H2 (g) + 5O2 (g) 4CO2 (g) + 2H2O (l) The value of So for this reaction is J/K. A) -432.4 B) -122.3 C) +122.3 D) +432.4 E) +689.3 2) The combustion of ethane in the presence of excess oxygen yields carbon dioxide and water: 2) 2C2H6 (g) + 7O2 (g) 4CO2 (g) + 6H2O (l) The value of So for this reaction is J/K. A) -151.0 B) +718.0 C) -620.9 D) -718.0 E) +151.0 1
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) Calcium Ca (s) 0 0 41.4 CaCl2 (s) -795.8-748.1 104.6 Ca2 + (aq) 226.7 209.2 200.8 Chlorine Cl2 (g) 0 0 222.96 Cl- (aq) -167.2-131.2 56.5 Oxygen O2 (g) 0 0 205.0 H2O (l) -285.83-237.13 69.91 Phosphorus P2 (g) 144.3 103.7 218.1 PCl3 (g) -288.1-269.6 311.7 POCl3 (g) -542.2-502.5 325 Sulfur S (s, rhombic) 0 0 31.88 SO2(g) -269.9-300.4 248.5 SO3(g) -395.2-370.4 256.2 3) The value of G at 25 oc for the decomposition of gaseous sulfur trioxide to solid elemental sulfur and gaseous oxygen, 3) 2SO3 (g) 2S (s, rhombic) + 3O2 (g) is kj/mol. A) +185.2 B) -370.4 C) +740.8 D) -740.8 E) +370.4 4) The value of G at 25 C for the formation of POCl3 from its constituent elements, 4) P2 (g) + O2 (g) + 3Cl2 (g) 2POCl3 (g) is kj/mol. A) +1,109 B) -1,005 C) -606.2 D) +606.2 E) -1,109 2
5) Given the thermodynamic data in the table below, calculate the equilibrium constant for the reaction: 5) 2 SO2 (g) + O2 (g) 2 SO3 (g) Substance Hf (kj/mol) (J/mol K) SO2 (g) -297 249 O2 (g) 0 205 SO3 (g) -395 256 A) 1.95 B) 2.32 1024 C) 3.82 1023 D) 1.06 E) More data are needed. 6) The equilibrium constant for a reaction is 0.48 at 25 C. What is the value of G (kj/mol) at this temperature? 6) A) 1.8 B) 1.5 102 C) 4.2 D) -4.2 E) More information is needed. 7) The equilibrium constant for the following reaction is 5.0 108 at 25 C. 7) N2 (g) + 3H2 (g) 2NH3 (g) The value of G for this reaction is kj/mol. A) 22 B) -22 C) -4.2 D) -25 E) -50 3
8) Consider the reaction: 8) Ag+ (aq) + Cl- (aq) AgCl (s) Given the following table of thermodynamic data at 298 ok: Substance Hf (kj/mol) S (J/K mol) Ag+ (aq) 105.90 73.93 Cl- (aq) -167.2 56.5 AgCl(s) -127.0 96.11 The value of K for the reaction at 25 C is. A) 1.8 104 B) 1.9 10-10 C) 3.7 1010 D) 5.4 109 E) 810 9) The first law of thermodynamics can be given as. A) the entropy of a pure crystalline substance at absolute zero is zero B) H rxn = n H f (products) - m H f (reactants) 9) C) E = q + w D) S = q rev /T at constant temperature E) for any spontaneous process, the entropy of the universe increases 10) A reaction that is spontaneous as written. A) will proceed without outside intervention B) has an equilibrium position that lies far to the left C) is also spontaneous in the reverse direction D) is very rapid E) is very slow 10) 11) Which one of the following is always positive when a spontaneous process occurs? 11) A) Suniverse B) Huniverse C) Ssurroundings D) Hsurroundings E) Ssystem 4
12) The second law of thermodynamics states that. A) the entropy of a pure crystalline substance is zero at absolute zero B) E = q + w C) for any spontaneous process, the entropy of the universe increases D) S = qrev/t at constant temperature 12) E) H rxn = n H f (products) - m H f (reactants) 13) S is positive for the reaction. A) BaF2 (s) Ba2+ (aq) + 2F- (aq) 13) B) CO2 (g) CO2 (s) C) 2NO2 (g) N2O4 (g) D) 2H2 (g) + O2 (g) 2H2O (g) E) 2Hg (l) + O2 (g) 2HgO (s) 14) Which one of the following processes produces a decrease in the entropy of the system? A) dissolution of solid KCl in water B) melting ice to form water C) freezing water to form ice D) boiling water to form steam E) mixing of two gases into one container 14) 15) Which reaction produces a decrease in the entropy of the system? A) H2O (l) H2O (g) 15) B) CaCO3 (s) CaO (s) + CO2 (g) C) 2C (s) + O2 (g) 2CO (g) D) 2H2 (g) + O2 (g) 2H2O (l) E) CO2 (s) CO2 (g) 5
16) The standard Gibbs free energy of formation of is zero. 16) (a) H2O (l) (b) O (g) (c) H2 (g) A) (a) only B) (b) only C) (c) only D) (b) and (c) E) (a), (b), and (c) 17) For the reaction 17) C2H6 (g) C2H4 (g) + H2 (g) H is +137 kj/mol and S is +120 J/K mol. This reaction is. A) spontaneous only at low temperature B) spontaneous only at high temperature C) nonspontaneous at all temperatures D) spontaneous at all temperatures 18) For a reaction to be spontaneous under standard conditions at all temperatures, the signs of H and S must be and, respectively. 18) A) +, + B) +, - C) -, + D) -, - E) +, 0 19) For the reaction 19) C(s) + H2O(g) CO(g) + H2(g) H = 131.3 kj/mol and S = 133.6 J/K mol at 298 K. At temperatures greater than C this reaction is spontaneous under standard conditions. A) 325 B) 273 C) 710 D) 983 E) 552 6
20) Consider the reaction: 20) Ag+ (aq) + Cl- (aq) AgCl (s) Given the following table of thermodynamic data, Substance Hf (kj/mol) S (J/mol K) Ag+ (aq) 105.90 73.93 Cl- (aq) -167.2 56.5 AgCl (s) -127.0 96.11 determine the temperature (in C) above which the reaction is nonspontaneous under standard conditions. A) 150.5 B) 1641 C) 432.8 D) 133.0 E) 1235 21) Consider the reaction: 21) NH3 (g) + HCl (g) NH4Cl (s) Given the following table of thermodynamic data, Substance Hf (kj/mol) S (J/mol K) NH3 (g) -46.19 192.5 HCl (g) -92.30 186.69 NH4Cl (s) -314.4 94.6 determine the temperature (in C) above which the reaction is nonspontaneous. A) This reaction is spontaneous at all temperatures. B) 618.1 C) 432.8 D) 1235 E) 345.1 22) With thermodynamics, one cannot determine. A) the direction of a spontaneous reaction B) the temperature at which a reaction will be spontaneous C) the extent of a reaction D) the speed of a reaction E) the value of the equilibrium constant 22) 7
23) Which one of the following statements is true about the equilibrium constant for a reaction if G for the reaction is negative? 23) A) K = 0 B) K = 1 C) K < 1 D) K > 1 E) More information is needed. 8