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1 8 4               Basic physical chemistry

            6. 1 4 .   (a)  Yes.  (b)  No.  Hint:  Determine  whether  or  not  any  of
                     the  oxidation  numbers  of any  of the  atoms  is  changed  by
                     the reaction.
                                                  2
                     2Pb(s) +  O  z(aq) +  2 H 2 0(l) � 2Pb + ( aq) +  4 0H - (aq)
            6  . 1 5  .
            6. 1 6 .   4P4(s) +  2 0H - ( aq) + 1 2 H 2 0(l)� 1 2H2P02- (aq) + 4PH3(aq) .
                             1
                     Hint: See  Exercises 6.2-6.4.
            6. 1 7 .    02(g) i s   the oxidant and C H 20 (s) the reductant.
                                                  6
                                            6
                                               1
                        2
                                  2
                             )
            6.  8 .    Mn + ( aq ,   Fe + ( aq),  Ag + (aq),  03(aq).  Hint: See Table  6.2
              1
                     and associated discussion in the text.
            6. 1 9 .   (a)  Yes,  it will. (b) A reductant. (c) Both.  (d)  No, it will not.
                     Hint: See Table  . 2   and associated discussion in  the text.
                                    6
            6 . 2 0.   (a)  It  will .  �en =  1 . 22  V  .   (b)  It  will  not.   � en = - 0.78 1  V  .
                     Hint: See Exercise 6.6.
            6.2 1 .    aGO  =  1 .05 x  105  J ;   it  is  not  a  spontaneous  reaction.  Hint:
                                  )
                     Use Eq .  (6. 2 0 .
                        =
            6.22.    Kc  4 .57 x  1 0 - 19• The equilibrium state for the reaction lies
                     far to the left.
            6 . 2 3 .   £cel l =   0 .   769   V  ;    aG =   -  1 .  48 x  105   J ;    the  forward  reaction  is
                               u
                      spontaneo s .   Hint: Use the Nernst equation (6. 2 5) to obtain
                                                                     t
                                               a
                     £    at 250K from  �e ll ·    Use  n   analogous expression  o   Eq.
                       cell
                     (6. 2 0) to obtain aG at 250K.
            6 . 2 4.   Maximum voltage = 1 2 . 2 46 V.
               5
            6.2 .    [H + ( aq)] = 1 . 3  x  1 0 - 3  M  .   Hint: Use Eq.  (6.26).
            6.26.    �ell =  - 0.046  V.  The  reaction  is  not  spontaneous  u n der
                      standard condition .
                                      s
                     Solution: HS03 (aq) + H 2 0(l) �
                              HS0 - ( aq) + 2H + (aq) + 2e -
                                   4
                      From Eq. (6.20)
                                         aV° = -  n F�en
                     Therefore,



                      where  n =  2   and  F  =  96,489  C  and,  from  Eq .  (2.34),  a(JO
                                                    l . 2  V  .   Since aCo  is  nega­
                      = - 227  kJ  mol - 1 .   Hence,  �ell =
                      tive  (and  �en positive),  the  reaction  is  spontaneous  under
                      standard conditions .
                      Fe 2 +  (aq)
            6.27.              782
                     FeH (aq)
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