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1 Which of the following substances has the lowest standard molar entropy (S °) at 25°C?A) CH3 OH(l ) B) CO(g ) C) MgO(s ) D) H2 O(l ) E) CaCO3 (s ) 2 Select the correct statement of a law of thermodynamics.A) The enthalpy of the universe is constantly increasing. B) The entropy of the universe is constant. C) The entropy of an element in its standard state at 25°C is zero. D) Every spontaneous process is accompanied by an increase in total entropy. E) Every spontaneous process is accompanied by a decrease in the enthalpy of the system. 3 Calculate ΔS º for the following reaction: 4Cr(s ) + 3O2 (g ) → 2Cr2 O3 (s ) Data: Standard molar entropies, S º (J/mol. K): Cr(s ), 23.8; O2 (g ), 205.1; Cr2 O3 (s ), 81.2A) 548.1 J/K B) 147.7 J/K C) -147.7 J/K D) -548.1 J/K E) -66.5 J/K 4 Consider the reaction: 4NH3 (g ) + 3O2 (g ) → 2N2 (g ) + 6H2 O(g ) For this reaction, ΔS º is +128.2 J/K. Use this value and the following standard molar entropies to calculate the standard molar entropy of NH3 (g ).S º (J/mol•K): O2 , 205.0; N2 , 191.5; H2 O, 188.7A) 193 J/mol•K B) 95.8 J/mol•K C) 383.0 J/mol•K D) 0 J/mol•K E) 47.0 J/mol•K 5 When crystalline solid barium hydroxide octahydrate and crystalline solid ammonium nitrate are mixed in a beaker at room temperature, a spontaneous reaction occurs. The temperature of the beaker contents rapidly falls to below 0ºC. Use this information to decide whether the reaction is exothermic or endothermic and what the signs of ΔH and ΔS are.A) endothermic; ΔH > 0;ΔS > 0 B) exothermic; ΔH < 0;ΔS > 0 C) endothermic; ΔH < 0;ΔS < 0 D) endothermic; ΔH < 0;ΔS > 0 E) exothermic; ΔH > 0;ΔS < 0 6 Which of the following is true for a system at equilibrium?A) ΔS sys = ΔS surr B) ΔS sys = -ΔS surr C) ΔS sys = ΔS surr = 0 D) ΔS univ > 0 E) ΔS surr > ΔS sys 7 Consider the reaction C9 H20 (l ) + 14O2 (g ) → 9CO2 (g ) + 10H2 O(g ) for which ΔG ºf is -5848 kJ at 25ºC. Use this value and the following standard free energies of formation to calculate ΔG ºf for liquid nonane, C9 H20 . ΔG ºf data (kJ/mol): O2 (g ), 0.0; CO2 (g ), -394.4; H2 O(g ), -228.6A) -610 kJ/mol B) +610 kJ/mol C) 12 kJ/mol D) 635 kJ/mol E) -635 kJ/mol 8 Consider the following reactions and ΔG º values: CaCO3 (s ) → CaO(s ) + CO2 (g ) ΔG º = + 130 kJ 3CaO(s ) + 2H3 PO4 (aq ) → Ca3 (PO4 )2 (s ) + 3H2 O(l ) ΔG º = - 512 kJ Calculate ΔG º for the reaction: 3CaCO3 (s ) + 2H3 PO4 (aq ) → Ca3 (PO4 )2 (s ) + 3CO2 (g ) + 3H2 O(l )A) -382 kJ B) +382 kJ C) -122 kJ D) +122 kJ E) -902 kJ 9 A certain reaction has ΔH º = -14.2 kJ and ΔS º = +87.9 J/K. What is the value of ΔG º for this reaction? (Temperature is 25º
C)A) +40.4 kJ B) -16.4 kJ C) -26200 kJ D) -40.4 kJ E) -7820 kJ 10 Predict the signs of ΔH °, ΔS °, and ΔG ° for the vaporization of liquid water at 150°C.A) ΔH ° > 0, ΔS ° > 0, ΔG ° > 0 B) ΔH ° < 0, ΔS ° < 0, ΔG ° < 0 C) ΔH ° > 0, ΔS ° < 0, ΔG ° > 0 D) ΔH ° > 0, ΔS ° > 0, ΔG ° < 0 E) none of the above 11 Hydrogen sulfide decomposes according to the following reaction: 2H2 S(g ) → 2H2 (g ) + S2 (g ) For this reaction at 298 K, ΔS ° = 78.1 J/K, ΔH ° = 169.4 kJ, and ΔG ° = 146.1 kJ. Calculate the value of ΔG ° at a temperature of 700. K.A) 41 kJ B) 83 kJ C) 115 kJ D) 143 kJ E) none of the above 12 Sodium carbonate can be made by heating sodium hydrogen carbonate: 2NaHCO3 (s ) → Na2 CO3 (s ) + CO2 (g ) + H2 O(g ) For this reaction, ΔH ° = 128.9 kJ and ΔS ° = 321 J/K. At approximately what temperature will K = 1?A) 401.6 K B) 401.6ºC C) 33.1 K D) 33.1ºC E) none of the above 13 A reaction has a value of ΔH = -249.6 kJ at 85ºC. Above this temperature the reaction is spontaneous; below it, it is not spontaneous. Calculate ΔS at this temperature.A) 697.2 J/K B) 1434 J/K C) -1434 J/K D) -697.2 J/K E) -2.936 x 103 J/K 14 A reaction has an equilibrium constant K c = 7.0 at 35ºC. Calculate the value of ΔG ° for the reaction.A) -4.98 kJ B) -2.46 kJ C) -5.66 kJ D) -2.16 kJ E) none of the above 15 For a system at equilibrium, ΔG is _____.A) positive B) negative C) zero D) equal to ΔH E) equal to -TΔS