A solution initially contains and

CHEMISTRY · Single correct · A Level · Chemistry · Electrode potentials · Electrode potentials

Problem

A solution initially contains

\mathrm{I_2(aq)}

and

\mathrm{Br^{-}(aq)}

. No observable reaction occurs. Which of the following best accounts for the absence of a reaction? (a)

\mathrm{Br^{-}}

is already at its lowest possible oxidation state, so it cannot be oxidized any further by

\mathrm{I_2}

. (b) The bond energy of

\mathrm{I_2}

is higher than that of

\mathrm{Br_2}

, making the reaction endothermic and therefore non-spontaneous. (c)

\mathrm{I_2}

is a weaker oxidizing agent than

\mathrm{Br_2}

because the standard reduction potential of the

\mathrm{I_2/I^{-}}

couple is lower than that of the

\mathrm{Br_2/Br^{-}}

couple; therefore, it cannot oxidize

\mathrm{Br^{-}}

. (d) The standard reduction potential of the

\mathrm{I_2/I^{-}}

couple is higher than that of the

\mathrm{Br_2/Br^{-}}

couple, so no electron transfer occurs between

\mathrm{I_2}

and

\mathrm{Br^{-}}