Question
Using the standard electrode potentials given in Table $3.1,$ predict if the reaction between the following is feasible:
$Br_2\ (aq)$ and $Fe^{2+}\ (aq).$

Answer

$\ \ \ \text{Br}_{2\text{(aq)}}+2\text{e}^-\ \ \xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ } 2\text{Br}^{-}_\text{(aq)} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ;\ \ \ \ \ \ \ \ \ \ \ \ \text{E}^\circ=+1.09\ \text{V}\\\text{Fe}^{2+}_\text{(aq)}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ } \text{Fe}^{3+}_{\text{(aq)}}+\text{e}^-\big]\times2\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ;\ \ \ \ \ \ \ \ \ \ \ \text{E}^\circ=-0.77\ \text{V}\\\overline{\text{Br}_\text{2(aq)}+2\text{Fe}^{2+}_\text{(aq)}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ }2\text{Br}^{-}_\text{(aq)}+2\text{Fe}^{3+}_\text{(aq)} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ;\ \ \ \ \ \ \ \ \ \ \ \ \text{E}^\circ=+0.32\ \text{V}}$
Since $E^\circ$ for the overall reaction is positive, the reaction between $Br^2\ (aq)$ and $Fe^{2+}\ (aq)s$ is feasible.

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