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  4. Consider the half-cell reduction reaction :- Mn2++2e-→ Mn, E0=-1.18 V Mn2+→ Mn3++e-, E0=-1.51 V The E° for the reaction 3 Mn2+→ Mn0+2Mn3+ and possibility of the forward reaction are respectively :

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Q. Consider the half-cell reduction reaction :-
$Mn^{2+}+2e^{-}\to Mn, E^{0}=-1.18 V$
$Mn^{2+}\to Mn^{3+}+e^{-}, E^{0}=-1.51 V$
The $E^\circ$ for the reaction $3 Mn^{2+}\to Mn^{0}+2Mn^{3+}$ and possibility of the forward reaction are respectively :

NEETNEET 2013Electrochemistry

Solution:

Standard electrode potential of reaction will not change due to multiply the half-cell reactions with some numbers,
To get the main eq we have to reverse 2 nd equation and add them
So $E _{3}= E _{2}+ E _{1}$
$E _{3}=-1.18+(-1.51)$
$E _{3}=-2.69\, V$
The reaction is not possible as the $\Delta G$ will come +ve for this case and that indicates reaction is non-spontaneous.