Electrochemistry

Electrochemistry

Question

Given below are the half-cell reactions
Mn2+ + 2e- → Mn; Eo = - 1.18 eV
2(Mn3+ + e- →Mn2+); Eo = +1.51 eV
The Eo for 3Mn2+ → Mn + 2Mn3+ will be

  • -2.69 V; the reaction will not occur

  • -2.69 V; the reaction will occure

  • -0.33 V; the reaction will not occur

  • -0.33 V; the reaction will occur

Answer

A.

-2.69 V; the reaction will not occur

Standard element potential of reaction [ Eo] can be calculated as
Eocell = ER-EP
where ER = SRP of reactant
EP = SRP of product
If Eocell = +ve, then the reaction is spontaneous otherwise non-spontaneous.
Mn to the power of 3 plus end exponent space rightwards arrow with straight E subscript 1 superscript straight o space equals space 1.51 space straight V on top space Mn to the power of 2 plus end exponent
Mn to the power of 2 plus end exponent space rightwards arrow with straight E subscript 2 superscript straight o space equals space minus space 1.18 space straight V on top space Mn
therefore, For Mn2+ disproportionation
Eo = - 1.51 V - 1.18 V = - 2.69 V < 0

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