Chemistry 112

Exam 5

 

 

                                                                                    Name:_______________________

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ε  = ε° –  (0.0591/n)log(Q)   Volt ~ J/C,  Amp ~ C/sec,  F = 96485 C/mole e–

R = 8.314 J/K mole

 

1.      Explain why:

(A)   Some exothermic reactions do not occur spontaneously.

 

 

 

 

 

 

(B)   Some reactions with at negative DG proceed slowly or not at all.

 

 

 

 

 

 

 

2.        Calculate K for the reaction at 298K:  H2S(g)  +  CO2(g)  «  H2O(g)  +  COS(g)  DGf° for COS is – 166. kJ/mole.

 

 

 

 

 

 

 

 

 

 

3.      Calculate the Gibbs Free Energy for the reaction:  3H2(g) + N2(g) ® 2NH3(g) at 400K: with P(H2) = 200 atm, P(N2) = 100 atm, P(NH3) = 10 atm.

 

 

 

 

 

 

 

4.  Will NH3(s) melt at 200.K?  DH°fusion = 5.65 kJ/mole and S°fusion =  28.9J/K mole.

 

 

 

 

 

 

 

 

 

 

 

 

 

5.  The reaction: 2 NO2(g)  ®  N2O4 (g) is exothermic and spontaneous.

 

(A)     What is the sign for the DG for this reaction?

 

 

(B)     What is the sign of the DH for this reaction?

 

 

(C)     What is the sign of the DS for this reaction?

 

 

(D)    Is this reaction more favorable at high or low temperature?

 

 

6.   Sketch the cell diagram for the Galvanic cell based on the following overall reaction:    Ni  +  Fe3+  «  Ni2+   +  Fe2+

 

 

 

 

 

 

 

 

Write the line diagram

 

 

 

 

 

 

7.  (A)   Which is the best oxidizing agent out of the following:  OCl-,  Cd2+,  K+,  O2, H2O2?

 

(B)  Which is the best reducing agent out of the following:  Cl-,  Cd,  Na,  H2O, Mn2+?

 

(C)  Can 1.0 M HCl dissolve Fe(s)?

 

 

 

8.   How long will it take to electroplate out 2.62 g of Ru from a solution of RuCl2 using a current of 2.50 Amps?

 

 

 

 

 

 

 

 

 

 

9.  A Galvanic cell consists of Ag+/Ag and Cu/Cu2+ solution.  What is the voltage if the [Ag+] = .010M and [Cu2+] = 2.0M?

 

 

 

 

 

 

 

 

 

 

 

 

10.  Calculate e° and DG° for the galvanic cell based on the two half reactions:

 

H2O2 +  2 H+  + 2e-  ®  2 H2O

Br2  +  2e-  ®  2Br –