Exam 4 due day of final exam Tues Dec 16th

CHM152 Bring Back Exam 4 100 Pts Fall 20014 Name:________________
Due at time of final exam Dec. 16th . Show all work to receive credit.
1. Given the following table of thermodynamic data,
substance
PCl3(g)
PCl3(l)
ΔHfo
-288.07 kJ/mol
-319.6
So
311.7 J/mol-K
217
determine the normal boiling point (in oC) of PCl3.
2. ΔSo will be positive for the reaction __________.
a) 2H2(g) + O2(g)  2H2O(g)
b) 2NO2(g)  N2O4(g)
c) Hè(aq) + F¨(aq)  HF(aq)
d) BaF2(s)  Ba2+(aq) + 2F¨(aq)
e) 2Hg(l) + O2(g)  2HgO(s)
Explain your answer.
3. The process of __________ causes a decrease in the entropy of the system.
a) boiling water to form steam
b) dissolution of solid KCl in water
c) mixing of two gases into one container
d) freezing water to form ice
e) melting ice to form water
Explain your answer.
4. Which one of the following reactions would have a positive value for ΔSo?
a) Ba(OH)2(s) + CO2(g)  BaCO3(s) + H2O(l)
b) N2(g) + 3H2(g)  2NH3(g)
c) 2SO3(g)  2SO2(g) + O2(g)
d) AgNO3(aq) + HCl(aq)  AgCl(s) + HNO3(aq)
e) freezing water to form ice
Explain your answer.
5. Look up the Ksp of Mg(OH)2 and then determine the pH of a 1.0 x 10-3 M Mg(OH)2 solution.
Show work to justify your answer.
6. Which molecule below should have the highest gas-phase absolute entropy at 25oC?
a) H2
b) C2H6 c) C2H2 d) CH4 e) C2H2
Explain your answer.
7. The solubility product for CrF3 is Ksp = 6.6 x 10–11. What is the molar solubility of CrF3?
Show work to justify your answer.
8. Consider the following table of thermodynamic data. All values are tabulated for 25oC.
Substance
_______
C2H2(g)
C2H4(g)
C2H6(g)
H2(g)
H2O(g)
C2H5OH(l)
ΔGof (kJ/mol)
______
209
68
-33
0
-229
-175
So (J/mol•K)
______
201
219
230
131
189
161
What is the value of ΔHo (in kJ) for the reaction described below? Assume the reaction is performed at
25oC.
C2H2(g) + 2H2(g)  C2H6(g)
9.
A precipitate forms when 250 mL of 0.33 M Na2CrO4 are added to 250 mL of 0.12 M AgNO3.
Ksp(Ag2CrO4) = 1.1 x 10–12 . What is the concentration of the Ag+ ion remaining in solution?
Show work to justify your answer.
-
10. Consider the reaction: Ag+(aq) + Cl (aq)  AgCl(s)
Given the following table of thermodynamic data,
substance
Ag+(aq)
Cl-(aq)
AgCl(s)
ΔHfo
105.90 kJ/mol
-167.2
-127.0
So
73.93 J/mol-K
56.5
96.11
determine the temperature (in oC) above which the reaction is nonspontaneous.
11. Calculate the equilibrium constant of the reaction below at 25oC.
2SO2(g) + O2(g) → 2SO3(g)
Substance
________
SO2(g)
O2(g)
SO
ΔHof(kJ/mol)
_______
-297
0
(g)
-395
So (J/mol•K)
_________
249
205
256
12. The equilibrium constant for a reaction is 0.48 at 25oC. What is the value of ΔGo (kJ) at this
temperature? (R = 8.314 J/K•mol)
13. The molar solubility of tin(II) iodide is 1.28 x 10–2 mol/L. What is Ksp for this compound?
Show work to justify your answer.
14. The Ksp
for PbCl2 is 2.4 x 10–4, will a precipitate of PbCl2 form when 0.10 L of 3.0 x 10–2 M
Pb(NO3)2 is added to 400 mL of 9.0 x 10–2 M NaCl? Show work to justify your answer.
15. Balance the following redox reaction in acidic solution.
H2S + MnO4– → Mn2+ + SO42– (acidic solution)
16. Balance the following redox reaction in basic solution.
H2O + MnO4– + I– → MnO2 + IO3– (basic solution)
-
17. The half-reaction occurring at the anode in the voltaic reaction 3MnO (aq) + 24H+(aq) + 5Fe(s) 
3Mn2+(aq) + 5Fe3+(aq) + 12H2O(l) is
-
a) MnO (aq) + 8H+(aq) + 5e-  Mn2+(aq) + 4H2O(l)
-
b) 2MnO (aq) + 12H+(aq) + 6e-  2Mn2+(aq) + 3H2O(l)
c) Fe(s)  Fe3+(aq) + 3ed) Fe(s)  Fe2+(aq) + 2ee) Fe2+(aq)  Fe3+(aq) + e-
18. What is the purpose of the salt bridge in an electrochemical cell?
19. For the reaction, Fe3+ + e-  Fe2+, E o = 0.77V. What is the value of the standard reduction potential
for the reaction, 49Fe3+ + 49e-  49Fe2+?
20. The two electrodes Cr(s)/Cr3+(aq) and Fe(s)/Fe2+(aq) are combined to afford a spontaneous
electrochemical reaction. The standard reduction potentials in V for Cr3+(aq) and Fe2+(aq) are -0.74 and
-0.44, respectively. Calculate Eo for the cell (in V).
21. Which one of the following types of elements is most likely to be good oxidizing agents?
a) alkali metals
b) lanthanides
c) alkaline earth elements
d) transition elements
e) halogens
Explain your answer.
22. Bromine can oxidize each of the metals below except
Substance
Br2
Ag
Pt
Cu
Pd
Li
Eo (v)
1.09
0.80
1.20
0.34
0.83
-3.05
a) Ag b) Pt c) Cu d) Pd
Explain your answer.
e) Li
23. Given the following information
Half-reaction
Sn4+(aq) + 2e-  Sn2+(aq)
Fe2+(aq) + 2e-  Fe(s)
Fe3+(aq) + e-  Fe2+(s)
Cr3+(aq) + 3e-  Cr(s)
Eored
+0.154 V
-0.440
+0.771
-0.74
determine the standard potential (in V) of a cell based on the reaction:
Sn2+(aq) + 2 Fe3+(aq)  2 Fe2+(aq) + Sn4+(aq)
24. What is meant by cathodic protection?
25. Given the following information
Half-reaction
Sn2+(aq) + 2e-  Sn4+(aq)
Fe2+(aq) + 2e-  Fe(s)
Fe3+(aq) + e-  Fe2+(s)
Cr3+(aq) + 3e-  Cr(s)
Eored
+0.154 V
-0.440
+0.771
-0.74
which of the following reactions will occur spontaneously as written?
a) Sn4+(aq) + Fe3+(aq)  Sn2+(aq) + Fe2+(aq)
b) 3Fe(s) + 2Cr3+(aq)  2Cr(s) + 3Fe2+(aq)
c) Sn4+(aq) + Fe2+(aq)  Sn2+(aq) + Fe(s)
d) 3Sn4+(aq) + 2Cr(s)  2Cr3+(aq) + 3Sn2+(aq)
e) Fe(s) + 2Fe3+(aq)  3Fe2+(aq)
Justify your answer.
26. Explain the difference between the reaction quotient, Q, and the equilibrium constant, K.
27. Calculate the equilibrium constant for the following reaction given that Eo for Cr2O72-/Cr3+ is 1.36 V
and for S2O32-/S4O62- is 0.17 V.
Cr2O72- + 6S2O32- + 14H+  2Cr3+ + 3S4O62-- + 7H2O
28. The standard reduction potentials in V for Zn2+ and Cu2+ are -0.76 and +0.34, respectively. What is
the potential of the cell (in V) represented below?
Zn(s) | Zn2+(1.00M) || Cu2+(0.100M) | Cu (s)
29. Given the following information
Half-reaction
Eored
Cu2+(aq) + 2e-  Cu(s)
Ni2+(aq) + 2e-  Ni(s)
+0.337 V
-0.28 V
determine the potential (in V) of an electrochemical cell in which the concentration of nickel(II) ion is
0.155 M and the concentration of copper(II) ion is 0.352 M. (T = 298 K)
30. Given the following information
Half-reaction
2 H+(aq) + 2e-  H2(g)
Sn2+(aq) + 2e-  Sn(s)
Eredø
+0.00 V
-0.136 V
Consider an electrochemical cell based on the reaction:
2 H+(aq) + Sn(s)  Sn2+(aq) + H2(g)
Determine which of the following actions would increase the measured cell potential.
a) increasing the pressure of hydrogen gas in the hydrogen cell
b) increasing the tin(II) ion concentration
c) lowering the pH in the cathode compartment
d) increasing the pH in the cathode compartment
e) any of these things will increase the measure cell potential
Explain your answer.
31. What mass of chromium could be deposited by electrolysis of an aqueous solution of Cr2(SO4)3
for 60.0 minutes using a constant current of 10.0 amperes? (One Faraday = 96,500 coulombs.)
32.
Fe2+ + 2e- Fe
Zn2+ + 2e-  Zn
Al3+ + 3e-  Al
Mg2+ + 2e-  Mg
Cu2+ + 2e  Cu
Eo = -0.44 V
Eo = -0.76 V
Eo = -1.67 V
Eo = -2.38 V
Eo = +0.34 V
From a consideration of these data, determine which of the following species will oxidize Fe to F2+.
a. Zn2+
b. Al3+
c. Mg2+
d. Cu2+
e. none of these
33. The standard reduction potentials in V for Ag+ to Ag and Fe3+ to Fe2+ are +0.80 and +0.77,
respectively. Calculate ΔGo (in kJ) for the following reaction. (F = 96,500 J/V•mol)
Ag+(aq) + Fe2+(aq) Ñ Ag(s) + Fe3+(aq)

Download Report