question_answer

The rusting of iron takes place as follows \[2{{H}^{+}}+2{{e}^{-}}+1/2{{O}_{2}}\to {{H}_{2}}O(l);\] \[{{E}^{o}}=+1.23\,V\] \[F{{e}^{2+}}+2{{e}^{-}}\to Fe(s);\,\,{{E}^{o}}=-\,0.44\,V\] Calculate \[\Delta G{}^\circ \] for the net process.

A) \[-\,152\] kJ \[mo{{l}^{-1}}\]

B) \[-\,161\]kJ \[mo{{l}^{-1}}\]

C) \[-\,322\]kJ \[mo{{l}^{-1}}\]

D) \[-\,76\]kJ \[mo{{l}^{-1}}\]

Correct Answer: C

Solution :

[c] \[\Delta {{G}^{o}}=-nF{{E}^{o}}\] Applying. \[\Delta {{G}_{1}}^{o}+\Delta {{G}_{2}}^{o}=\Delta {{G}_{3}}^{o}\] \[\Delta {{G}_{3}}^{o}=(-\,2F\times 0.44)+(-\,2F\times 1.23)\] \[\Delta {{G}_{3}}^{o}=-(2\times 96500\times 0.44+2\times 96500\times 1.23)\]\[\Delta {{G}_{3}}^{o}=-322310J\] \[\therefore \Delta {{G}_{3}}^{o}=-322KJ\]