Given below are the half-cell reaction:
Mn2++2e⊖→Mn; E⊖=−1.18V
2(Mn3++e⊖→Mn2+; E⊖=+1.51V
The E⊖ for 3Mn2+→Mn+2Mn3+ will be:
(IIT-JEE 2014)
(c) -2.69 V; the reaction will not occur
Mn2++2e⊖→Mn; E⊖=−1.18V
2Mn2++→2Mn3++2e⊖; E⊖=−1.51V
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3Mn2+→Mn+2Mn3+
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E⊖cell=E⊖red+E⊖oxid
= -1.18 + (-1.51) = -2.69 V
Negative EMF reflects non-spontaneous cell reaction.