51. The standard cell potential ( ) for the reaction below is +0.63 V. At 25 °C, the cell potential for this reaction is ________ V when [Zn²⁺ ] = 3.0 M and [Pb²⁺ ] =2.0✖10^-4M.

Pb²⁺(aq) + Zn (s) → Zn²⁺(aq) + Pb (s)
(A)0.51
(B)0.86
(C) 0.40
(D)0.75

47. Which of the following reactions is a redox reaction?(a) K2CrO4 + BaCl2 → BaCrO4 + 2KCl(b) Pb22+ + 2Br- → PbBr(c) Cu + S → CuS (A)(a) only (B)(b) only (C) (c) only(D)(a) and (c)

48. The purpose of the salt bridge in an electrochemical cell is to ________. (A)maintain electrical neutrality in the half-cells via migration of ions (B)provide a source of ions to react at the anode and cathode (C) provide oxygen to facilitate oxidation at the anode (D) provide a means for electrons to travel from the anode to the cathode

49. Consider an electrochemical cell based on the reaction:2H+ (aq) + Sn (s) → Sn2+ (aq) + H2 (g) Which of the following actions would not change the measured cell potential? (A)lowering the pH in the cathode compartment (B)addition of more tin metal to the anode compartment (C) increasing the tin (II) ion concentration in the anode compartment (D) increasing the pressure of hydrogen gas in the cathode compartment

50. What is the cathode in an alkaline battery? (A)MnO2 (B)KOH (C) Zn powder(D)Mn2O3

52. The first law of thermodynamics can be given as ________. (A)ΔE = q + w (B)(C) for any spontaneous process, the entropy of the universe increases (D) the entropy of a pure crystalline substance at absolute zero is zero

53. When a system is at equilibrium, ________. (A)the reverse process is spontaneous but the forward process is not (B)the forward and the reverse processes are both spontaneous (C) the forward process is spontaneous but the reverse process is not (D) the process is not spontaneous in either direction

54. The second law of thermodynamics states that ________. (A)ΔE = q + w (B)ΔH°rxn = Σ nΔH°f (products) - Σ mΔH°f (reactants) (C) for any spontaneous process, the entropy of the universe increases (D) the entropy of a pure crystalline substance is zero at absolute zero

55. ΔS is positive for the reaction ________. (A)2H2 (g) + O2 (g) → 2H2O (g) (B)2NO2 (g) → N2O4 (g) (C) CO2 (g) → CO2 (s)(D)BaF2 (s) → Ba2+ (aq) + 2F- (aq)

複選題56. With thermodynamics, one cannot determine ________. (A)the speed of a reaction (B)the direction of a spontaneous reaction (C) the extent of a reaction (D) the value of the equilibrium constant

57. Photoionization processes (e.g., N2 + hν → N2+ + e-) remove UV of ＜ 150 nm. Which photoreaction is the principal absorber of UV in the 150-200 nm range in the upper atmosphere? (A)N2 + hν → 2N (B)O2 + hν → 2º (C) O3 + hν → O2 + O(D)N2 + O2 + hν → 2NO