(A) (a) Calculate the standard Gibbs energy (Δ_r G^°) of the following reaction at 25 °C: 3 + 2 Au ( s )+ Ca^2+(1 M ) → Au^3+(1 M )+ Ca ( s );…

Calculate the standard Gibbs energy $\displaystyle \left(\Delta_{\mathrm{r}} \mathrm{G}^{\circ}\right)$ of the following reaction at $\displaystyle 25$ °C : $\displaystyle 3$ + $\displaystyle 2$ \[\begin{aligned} & \mathrm{Au}(\mathrm{~s})+\mathrm{Ca}^{2+}(1 \mathrm{M}) \rightarrow \mathrm{Au}^{3+}(1 \mathrm{M})+\mathrm{Ca}(\mathrm{~s}) \\ & \mathrm{E}_{\mathrm{Au}^{3+} / \mathrm{Au}}^{\circ}=+1.5 \mathrm{~V}, \mathrm{E}_{\mathrm{Ca}^{2+} / \mathrm{Ca}}^{\circ}=-2.87 \mathrm{~V} \end{aligned} \] Predict whether the reaction will be spontaneous or not at $\displaystyle 25$ °C. \[\left[1 \mathrm{~F}=96500 \mathrm{C} \mathrm{~mol}^{-1}\right] \]

Tarnished silver contains $\displaystyle \mathrm{Ag}_{2} \mathrm{~S}$. Can this tarnish be removed by placing tarnished silverware in an aluminium pan containing an inert electrolytic solution such as NaCl ? The standard electrode potential for half reaction : \[\begin{aligned} & \mathrm{Ag}_{2} \mathrm{~S}(\mathrm{~s})+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{Ag}(\mathrm{~s})+\mathrm{S}^{2-} \text { is }-0.71 \mathrm{~V} \text { and for } \\ & \mathrm{Al}^{3+}+3 \mathrm{e}^{-} \longrightarrow 2 \mathrm{Al}(\mathrm{~s}) \text { is }-1.66 \mathrm{~V} \end{aligned} \]

OR 33. (B) (a) Define the following : $\displaystyle 2+3$

Cell potential

Fuel cell

Calculate emf of the following cell at $\displaystyle 25$ °C : \[\mathrm{Zn}(\mathrm{~s})\left|\mathrm{Zn}_{(0.1 \mathrm{M})}^{2+}\right|\left|\mathrm{Cd}_{(0.01 \mathrm{M})}^{2+}\right| \mathrm{Cd}(\mathrm{~s}) \] Given : $\displaystyle \mathrm{E}_{\mathrm{Cd}^{2+} / \mathrm{Cd}}^{\circ}=-0.40 \mathrm{~V}$ \[\begin{aligned} & \mathrm{E}_{\mathrm{Zn}^{2+} / \mathrm{Zn}}^{\circ}=-0.76 \mathrm{~V} \\ & {[\log 10=1]} \end{aligned} \]