Please solve and kindly tell..When and why do we take into account the pressure of the reacting specied in the nernst equation....??! Like we have in this question . Also are there any.other modifications in the nernst equation...??

8 .     C o n s i d e r   t h e   f o l l o w i n g   c e l l   r e a c t i o n ,   2 F e s   +   O 2 g   +   4 H +   ( a q )     2 F e 2 +   ( a q )   +   2 H 2 O ( l ) , E °   =   1 . 67   V A t   F e 2 +   =   10 - 3   M ,   P O 2   =   0 . 1   a t m   a n d   p H   =   3 ,   t h e   c e l l   p o t e n t i a l   a t   25 °   C   i s a   1 . 47   V                                                                       b   1 . 77   V   c   1 . 87   V                                                                       d   1 . 57   V        

 

pH = - log[H+]
3 = - log[H+]
-antilog 3 = [H+]
Therefore, [H+] = 10-3 M

Oxidation half reaction:
Fe(s)  Fe2+ + 2e-     ] X 2
4H+ + O2 + 4e-  2H2O

Number of electrons involved, n = 4

Cell potential is given as,

Ecell = E°cell - 0.529n log[Fe2+]2[H+]4Ecell = 1.67 - 0.5294log [10-3]2[10-3]4Ecell = 1.67 - 0.13225 log 106Ecell = 1.67 - 0.13225×6Ecell = 1.67 - 0.7935 = 0.8765 V
 

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