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Chemistry · 2025 · 3 marks
CBSE 2025 · Region 1 · Set 2 · Q23
Calculate Δ_r G^° and log K_C of the reaction: Fe^2+( aq )+ Ag^+( aq ) → Fe^3+( aq )+ Ag ( s ) Given E_Ag^+ / Ag^°=0.80 V, E_Fe^3+ / Fe^2+^°=0.77 V […
Calculate $\displaystyle \Delta_{\mathrm{r}} \mathrm{G}^{\circ}$ and $\displaystyle \log \mathrm{K}_{\mathrm{C}}$ of the reaction : $\displaystyle \mathrm{Fe}^{2+}(\mathrm{aq})+\mathrm{Ag}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Fe}^{3+}(\mathrm{aq})+\mathrm{Ag}(\mathrm{s})$ Given $\displaystyle \mathrm{E}_{\mathrm{Ag}^{+} / \mathrm{Ag}}^{\circ}=0.80 \mathrm{~V}, \mathrm{E}_{\mathrm{Fe}^{3+} / \mathrm{Fe}^{2+}}^{\circ}=0.77 \mathrm{~V}$ \[\left[\mathrm{R}=8.314 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}, \mathrm{~F}=96500 \mathrm{C} \mathrm{~mol}^{-1}\right] \]
Marking-scheme solution
Eocell= Eocathode−Eoanode
=EoAg+/Ag−EoFe3+/Fe2+
= $\displaystyle 0.03$ V
△G0 =-nF Eocell
= -$\displaystyle 1$ x $\displaystyle 96500$ X $\displaystyle 0.03$
= -$\displaystyle 2895$ J/mol
= -$\displaystyle 2.895$ KJ/ mol
△G0 =-2.303RT log Kc
log Kc = -△G0 / 2.303RT
= $\displaystyle 2895$ / $\displaystyle 2.303$ x $\displaystyle 8.314$ X $\displaystyle 298$
log Kc =$\displaystyle 2895$ / $\displaystyle 5700$
= $\displaystyle 0.508$
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CBSE Class 12 Chemistry past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.