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Answer 1 · 2016-10-18T02:33:25

$MnO_2(s) +3Ag^(+) + 2H_2O(l) rarr MnO_4^(-) + 3Ag(s)darr + 4H^(+)$

Are charge and mass balanced?

$"Oxidation: " Mn(IV) rarr Mn(VII)$

$MnO_2(s) +2H_2O(l) rarr MnO_4^(-) + 4H^(+)+3e^-$ $(i)$ $;E^@=-1.68V$

$"Reduction: " Mn(IV) rarr Mn(VII)$

$Ag^(+) + e^(-) rarr Ag(s)$ $(ii)$ $;E^@=0.80V$

$"Overall: "1xx(i)+3xx(ii)$ ,

$MnO_2(s) +3Ag^(+) + 2H_2O(l) rarr MnO_4^(-) + 3Ag(s)darr + 4H^(+)$
$;E^@=-0.78V$

I looked up the electrode potentials, and the reaction is NOT feasible. Reduction of $Ag^(2+)$ would drive the reaction:

$Ag^(2+) + 2e^(-) rarr Ag(s)$ $(iii)$ $;E^@=1.99V$