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Can bromide ion reduce ferric ion ?

Just a query. In my opinion it can since bromide ion can undergo oxidation. Is my answer correct?

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You can predict this with the help of electrochemical series.

Electrochemical Series

On going up the series reducing power increases, for you case it can be seen that Fe is a better reducing agent than bromide ion as Fe is above Br2 so bromide can't reduce ferric ion.

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According to you the reaction will be:

2Br- + 2Fe(III) ---> Br2 + 2Fe(II) by balancing. Spontaneity can be checked out by using standard EMF of the cell formed

Hence standard emf E(cell)=E(Reduction) for {Fe(III)/Fe(II)} + E(oxidation) for {Br-/Br2}

Now using standard values we get E(Reduction) for {Fe(III)/Fe(II)}=+0.77 and E(oxidation) for {Br-/Br2}=-1.07 hence the E(cell) we get is =.77-1.07=-.3(negative)

We have (Delta)G=-n*F*E(cell) where (Delta)G is change in Gibb's Free Energy change n is no. of electrons(here n=2),F is Faraday's constant and E is Emf of cell(Standard)

If (Delta)G is negative then reaction is spontaneous and if (Delta)G is positive then non spontaneous. Clearly here E(cell) is negative hence (Delta)G is positive hence reaction is non-spontaneous and will not occur[NOTE THAT HERE CONCENTRATIONS OF IONS AND PRESSURE OF GAS IS TAKEN UNITY IN ITS SI UNITS.WE CAN MAKE IT SPONTANEOUS BY VARYING THE CONCENTRATION OF ION OR PARTIAL PRESSURE OF GAS]

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  • $\begingroup$ Can't there be a more obvious way to tell this ? $\endgroup$ – user2369284 Dec 26 '13 at 18:33
  • $\begingroup$ I guess no.U can't tell directly if the reaction is spontaneous or not.U have to take catch of thermodynamics. $\endgroup$ – Devgeet Patel Dec 26 '13 at 18:35

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