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CBSE Class 12 Chemistry 2022 Term 2 Delhi Set 3

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Question : 5 of 12
Marks: +1, -0
(a) Calculate ΔrG\Delta_r G^{\circ} and logKc\log K_c for the following cell:
Ni(s)+2Ag+(aq)Ni2+(aq)+2Ag(s)\mathrm{Ni}(s)+2\mathrm{Ag}^{+}(aq)\rightarrow\mathrm{Ni}^{2+}(aq)+2\mathrm{Ag}(s)
Given that EcellE^{\circ}_{\text{cell}}=1.05V,1F=96,500Cmol1=1.05\,\text{V},\,1\,\text{F}=96,500\,\text{C}\,\text{mol}^{-1}
OR
(b) Calculate the e.m.f. of the following cell at 298K298\,\text{K} :
Fe(s)Fe2+(0.001M)H+(0.01M)H2(g)\mathrm{Fe}(s)\vert\mathrm{Fe}^{2+}(0.001\,\text{M})\parallel\mathrm{H}^{+}(0.01\,\text{M})\vert\mathrm{H}_2(g)
(1 bar) | Pt (s)
Given that EcellE^{\circ}_{\text{cell}} =0.44V=0.44\,\text{V}
[log2=0.3010,log3=0.4771,log10=1][\log2=0.3010,\log3=0.4771,\log10=1]
Solution:  
According to the equation,
Ni+2Ag+Ni2++2Ag\mathrm{Ni}+2\mathrm{Ag}^{+}\rightarrow\mathrm{Ni}^{2+}+2\mathrm{Ag}
ΔG=nFE\Delta G=-nFE^{\circ}
 where ΔG=Gibb ’ free energy \text{ where }\Delta G=\text{Gibb}'\text{ ' free energy }
ΔG=2×96500×1.05\Delta G=-2\times96500\times1.05
N= No. of electrons gain or lost =2N=\text{ No. of electrons gain or lost }=2
ΔG=202.650kJ\Delta G=-202.650\,\text{kJ}
F= Faraday’s constant =96500F=\text{ Faraday's constant }=96500
E= Standard emf =1.05VE^{\circ}=\text{ Standard emf }=1.05\,\text{V}
The relation between Gibb's free energy and Equilibrium constant is given by equation
Ecell=0.0591nlogKcE^{\circ}_{\text{cell}}=\frac{0.0591}{n}\log K_c
logKc=1.05×20.0591=35.53\log K_c=-\frac{1.05\times2}{0.0591}=35.53
Kc=3.39×1035K_c=3.39\times10^{35}
OR
According to the equation,
Fe(s)+2H+(aq)Fe2+(aq)+H2(g)\mathrm{Fe}(s)+2\mathrm{H}^{+}(aq)\rightarrow\mathrm{Fe}^{2+}(aq)+\mathrm{H}_2(g)
Ecell=EcathodeEanodeE^{\circ}_{\text{cell}}=E^{\circ}_{\text{cathode}}-E^{\circ}_{\text{anode}}
Ecell=0(0.44)VE^{\circ}_{\text{cell}}=0-(-0.44)\,\text{V}
Ecell=+0.44VE^{\circ}_{\text{cell}}=+0.44\,\text{V}
By applying Nernst Equation,
Ecell=Ecell0.05912log[Fe2+][H+]2E_{\text{cell}}=E^{\circ}_{\text{cell}}-\frac{0.0591}{2}\log\frac{[\mathrm{Fe}^{2+}]}{[\mathrm{H}^{+}]^2}
Ecell=0.440.05912log0.001(0.01)2E_{\text{cell}}=0.44-\frac{0.0591}{2}\log\frac{0.001}{(0.01)^2}
Ecell=0.440.05912log10E_{\text{cell}}=0.44-\frac{0.0591}{2}\log10
Ecell=0.440.0295×1E_{\text{cell}}=0.44-0.0295\times1
Ecell=+0.410VE_{\text{cell}}=+0.410\,\text{V}
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