CHEM 2046 Fall 2011 Exam 3 Prof. Col. Charles R. Martin Form A
Instructions: Mark only one answer per question on the scantron. You have 1 h 55 min to complete
the test. Make sure you have entered your correct UFID and Form Code in the scantron before
1. Which of the following statements are correct?
(I) Homogeneous electron-transfer reactions occur across an interface.
(II) In homogeneous electron-transfer reactions the oxidizing and reducing agents are in the same phase.
(III) In homogeneous electron-transfer reactions the oxidizing and reducing agents are in separate phases.
(IV) Heterogeneous electron-transfer reactions occur across an interface.
(V) Heterogeneous electron-transfer reactions always involve solids.
(A) (I), (II) and (IV) (B) (III) and (IV) (C) (II) and (IV)
(D) (III), (IV) and (V) (E) (I), (II) and (V)
2. Arrange the following species in order of increasing reducing strength: H (g)2 Ag(s), Na(s), Fe(s).
(A) H 2g) > Ag(s) > Na(s) > Fe(s) (B) Na(s) > H 2g) > Ag(s) > Fe(s)
(C) H 2g) > Ag(s) > Fe(s) > Na(s) (D) Ag(s) > Fe(s) > Na(s) > H (g2
(E) Na(s) > Fe(s) > H (2) > Ag(s)
3. For the reaction 2H (2) + C H (2) 2 C H (g),2ΔG6 = –621.19 kJ/mol at 298 K. What is the ΔGat
this temperature when p(H ) 2 p(C H )2= 2(C H ) 2 160atm?
(A) –598.37 kJ/mol (B) –621.19 kJ/mol (C) –644.01 kJ/mol
(D) –609.78 kJ/mol (E) –611.28 kJ/mol
ΔG = ΔG°+ RTlnQ
4. Given E° (Ag /Ag) = 0.80 V, calculate the potential of a silver wire at 25° C in a solution of 0.05 M
AgNO . 3
(A) 0.88 V (B) 0.62 V (C) 0.98 V (D) 0.62 V (E) 0.72 V
E = E°– 0.0592 log (1/[Ag ]) +
5. For the reaction CaCO (s)3 CaO(s) + CO (g), K =22.5×10 p at 25°C. What is the ΔG for this
reaction at this particular temperature?
(A) 55 kJ/mol (B) –4.6 kJ/mol (C) –55 kJ/mol (D) 24 kJ/mol (E) 4.6 kJ/mol
ΔG°= – RTlnK p
6. Balance the following redox reaction in b–sic solution: –
OH + F 2F + F + 2 O 2
What are the coefficients for F 2nd H O?2
(A) 2, 2 (B) 2, 1 (C) 1, 1 (D) 1, 2 (E) 2, 4
2OH + 2F O2 + 2F + 2 O 2
3+ – 2+
7. Given Fe (aq) + e Fe (s) E°= 0.77 V
I2(s) + 2e 2I (aq) E°= 0.58 V
What is the equilibrium constant for the reaction 2Fe (aq) + 2I (aq) 2Fe (aq) + I (s) at 300 K?
(A) 2.4×10 6 (B) 1.6×10 3 (C) 5.0×10 14 (D) 4.1×10 –7 (E) 3.8×10 10
E°= E° –cat = 0.anoV – 0.58 V = 0.19 V
K = (RT/nF) ln E°(T = 300 K, hence cannot use 0.0592)
8. Calculate the half-cell potential for the half-reaction below at 25° C, when the partial pressure of H =2
0.3 atm and pH = 8.
2H 2(l) + 2e H (g)2+ 2OH (aq) E°= –0.83 V
(A) –1.20 V (B) –1.32 V– 2 (C) –1.02 V (D) –1.57 V (E) –0.46 V
E = E°– (0.0592/2) log (p [ H2 ] ) 9. The ΔG for reaction Hg 22+(aq) + Cl 2g) 2Hg (aq) + 2Cl (aq) is –84.92 kJ/mol. Given E°= 1.36 V
for the half-reaction Cl 2g) + 2e 2Cl (aq), what is the E°for the other half-reaction?
(A) 0.48 V (B) 1.80 V (C) 0.92 V (D) 2.24 V (E) 1.36 V
E°= – ΔG° /nF
E° ano° – Ecatccording to the full equation, Cl (g)/ Cl 2aq) should be the cathode)
10. Which of the following statements are correct about the cathode in a voltaic cell?
(I) Oxidation occurs at the cathode. (II) Reduction occurs at the cathode.
(III) Cations are attracted to the cathode. (IV) Anions are attracted to the cathode.
(V) The cathode has the more positive potential. (VI) The cathode has the more negative potential.
(A) (I), (III) and (V) (B) (I), (IV) and (V) (C) (II), (III) and (V)
(D) (II), (IV) and (VI) (E) (II), (III) and (VI)
11. The E for the following half-reaction is 0.59 V. In an experiment at 25° C the actual potential of the
electrode in a 0.005 M KMnO solut4on is found to be 0.78 V, what is the pH of the solution?