1.

E_(Mn)^(@)+7|""_(Mn)+2 = 1.5 V E_(Mn)^(@)+4|""_(Mn)+2 = 1.2 V, then E_(Mn)^(@)+7|""_(Mn)+4 is

Answer»

A) `0.3 V`
B) `0.1 V`
C) `1.7 V`
D) `2.1 V`

Solution :(c): `Mn^(7+)+5e^(-) to Mn^(2+) , E^(@)` = 1.5 V
`DeltaG_(1)^(@) = -NFE^(@) = -5 xx F xx 1.5 rArr -7.5` F...(i)
`Mn^(4+) + 2e^(-) to Mn^(2+), E^(@) = 1.2` V
`DeltaG_(2)^(@) = -nFE^(@) = -2xxFxx1.2 = -2.4` F...(ii)
On subtracting eqn (ii) from (i), we get,
`Mn^(7+) + 3E^(-) to Mn^(4+), E^(@) =` ?
`DeltaG_(3)^(@) = DeltaG_(1)^(@) - DeltaG_(2)^(@)`
`-3FE^(@) = -7.5 F-(-2.4 F) rArr -3FE^(@) = -5.1 F`
`:. E^(@)` = 1.7 V


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