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EXAM_3_solution_Form_A.pdf

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Department
Chemistry
Course
CHM 2046
Professor
Christou
Semester
Spring

Description
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 submission. 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 ]) + –10 o 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? 2 (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) o 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? – –
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