1. An electrochemical reaction involves the transfer of two electrons and has an
ID: 974478 • Letter: 1
Question
1. An electrochemical reaction involves the transfer of two electrons and has an equilibrium constant at 298 K of 1.68 × 104. What is E° for this reaction?
SO42- + 4Cr2+ + 8H+ H2S + 4Cr3+ + 4H2O
SO42- + 8Cr2+ + 8H+ H2S + 8Cr3+ + 4H2O
SO42-+ 8Cr2+ H2S + 8Cr3+
d. SO42- + 8Cr2+ + 10H+ H2S + 8Cr3+ + 4H2O
3. Standard free energies of formation for use in problems that follow:
Based on values in the preceding table, what is the standard free energy change for the reaction
C6H12O6(s) 2CO2(g) + 2CH3CH2OH(l)?
a. -221.1 kJ/mol
b. -208.5 kJ/mol
c. 348.0 kJ/mol
d. 173.3 kJ/mol
a. 0.250 V b. 0.125 V c. 0.287 V d. 0.0 V 2. What is the balanced redox equation for the reaction of SO42- with Cr2+ to give H2S and Cr3+ in acidic solution? a.SO42- + 4Cr2+ + 8H+ H2S + 4Cr3+ + 4H2O
b.SO42- + 8Cr2+ + 8H+ H2S + 8Cr3+ + 4H2O
c.SO42-+ 8Cr2+ H2S + 8Cr3+
d. SO42- + 8Cr2+ + 10H+ H2S + 8Cr3+ + 4H2O
3. Standard free energies of formation for use in problems that follow:
Compound G°f Compound G°f CO(g) -137.2 H2O(g) -228.572 CO2(g) -394.359 H2O(l) -237.129 C2H2(g) 209.2 CaC2(s) -64.9 C2H4(g) 68.12 Ca(OH)2(s) -898.6 CH3CH2OH(g) -168.49 CaO -604.0 CH3CH2OH(l) -174.78 CaCO3 -1128 C6H12O6 -917.2
Based on values in the preceding table, what is the standard free energy change for the reaction
C6H12O6(s) 2CO2(g) + 2CH3CH2OH(l)?
a. -221.1 kJ/mol
b. -208.5 kJ/mol
c. 348.0 kJ/mol
d. 173.3 kJ/mol
Explanation / Answer
1.
Apply
-RT*lnK= -nF*E°cell
E°cell = RT/(nF)*lnK
E°cell = 8.314*298/(2*96500)*ln(1.68*10^4) = 0.124894
E°cell = 0.124894 V; choose B
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