Which reaction is not feasible?

Which reaction is not feasible?
  1. $2 \mathrm{KI}+\mathrm{Br}_2 \rightarrow 2 \mathrm{KBr}+\mathrm{I}_2$
  2. $2 \mathrm{KBr}+\mathrm{I}_2 \rightarrow 2 \mathrm{KI}+\mathrm{Br}_2$
  3. $2 \mathrm{KBr}+\mathrm{Cl}_2 \rightarrow 2 \mathrm{KCl}+\mathrm{Br}_2$
  4. $2 \mathrm{H}_2 \mathrm{O}+2 \mathrm{~F}_2 \rightarrow 4 \mathrm{HF}+\mathrm{O}_2$

Solution

$2 \mathrm{KBr}+\mathrm{I}_2 \rightarrow 2 \mathrm{KI}+\mathrm{Br}_2$ reaction is not possible because $\mathrm{Br}^{-}$ion is not oxidised in $\mathrm{Br}_2$ with $\mathrm{I}_2$ due to higher electrode (oxidation) potential of $\mathrm{I}_2$ than bromine. Energetically favorable means no energy input needed for reaction to take place.

Asked in: NEET 2002

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