The spontaneous redox reaction/s among the following is/are (1) $2 \mathrm{Fe}^{3+}+\mathrm{Fe} ightarrow 3…
(1) $2 \mathrm{Fe}^{3+}+\mathrm{Fe} ightarrow 3 \mathrm{Fe}^{++}$
(2) $\mathrm{Hg}_{2}^{++} ightarrow \mathrm{Hg}^{++}+\mathrm{Hg}$
(3) $3 \mathrm{AgCl}+\mathrm{NO}+2 \mathrm{H}_{2} \mathrm{O} ightarrow 3 \mathrm{Ag}+3 \mathrm{Cl}^{-}+\mathrm{NO}_{3}^{-}+4 \mathrm{H}^{+}$
Given that
$\mathrm{E}_{\mathrm{Fe}^{+++} / \mathrm{Fe}^{++}}^{0}=0.77 \mathrm{~V}, \mathrm{E}_{\mathrm{Fe}^{++} / \mathrm{Fe}}^{0}=-0.44 \mathrm{~V}$
$\mathrm{E}_{\mathrm{Hg}_{2}^{++} / \mathrm{Hg}}^{0}=0.85 \mathrm{~V}, \quad \mathrm{E}_{\mathrm{Hg}^{++} / \mathrm{Hg}_{2}{ }^{++}}^{\mathrm{o}}=0.92 \mathrm{~V}$
$\mathrm{E}_{\mathrm{AgCl} / \mathrm{Ag}}^{\mathrm{o}}=0.22 \mathrm{~V}, \quad \mathrm{E}_{\mathrm{NO}_{3}^{-} / \mathrm{NO}}^{0}=0.96 \mathrm{~V}$
- $1$
- $1,2,3$
- $1,2$
- $1,3$
Solution
$\mathrm{E}_{\text {reaction }}^{0}=\mathrm{E}_{\mathrm{O} . \mathrm{A}}^{0}-\mathrm{E}_{\mathrm{R} . \mathrm{A}}^{0}$
$=0.77-(-0.44)$
$=+1.21 \mathrm{~V}$
$\mathrm{E}^{0}$ is positive so $\Delta \mathrm{G}$ is negative
$\therefore$ Spontaneous reaction
2) $\mathrm{Hg}_{2}^{++} ightarrow \mathrm{Hg}^{++}+\mathrm{Hg}$
$\mathrm{E}_{\text {redox Reaction }}^{0}=\mathrm{E}_{\mathrm{O.A}}^{0}-\mathrm{E}_{\mathrm{R} . \mathrm{A}}^{0}$
$=0.85-0.92$
$=-0.07$
$\mathrm{E}^{0}$ is negative so $\Delta \mathrm{G}$ is positive
$\therefore$ nonspontaneous reaction
3) $3 \mathrm{AgCl}+\mathrm{NO}+2 \mathrm{H}_{2} \mathrm{O} ightarrow 3 \mathrm{Ag}+3 \mathrm{Cl}^{-}+\mathrm{NO}_{3}^{-}+4 \mathrm{H}^{+}$
$\mathrm{E}_{\text {redox Reaction }}^{0}=\mathrm{E}_{\mathrm{O} . \mathrm{A}}^{0}-\mathrm{E}_{\mathrm{R} . \mathrm{A}}^{0}=0.22-0.96=-074 . \mathrm{V}$
$\mathrm{E}^{0}$ is negative so $\Delta \mathrm{G}$ is positive
$\therefore$ non-spontaneous reaction
Asked in: JEE-TOPICTESTS-CHEMISTRY