NEET Sample Paper NEET Sample Test Paper-90

  • question_answer
    \[S{{n}^{4+}}+2{{e}^{-}}\xrightarrow{{}}S{{n}^{2+}}\,\,E{}^\circ =0.13\,V\] \[B{{r}_{2}}+2{{e}^{-}}\xrightarrow{{}}2B{{r}^{-}}\,\,E{}^\circ =1.08\,V\] Calculate \[{{K}_{eq}}\] for the cell at \[20{}^\circ C\] formed by two electrodes

    A) \[{{10}^{41}}\]                      

    B)        \[{{10}^{32}}\]

    C) \[{{10}^{-32}}\]         

    D)         \[{{10}^{-42}}\]

    Correct Answer: B

    Solution :

    [b] \[S{{n}^{4+}}+2{{e}^{-}}\xrightarrow{{}}S{{n}^{2+}}E{}^\circ =0.13\,V\] \[B{{r}_{2}}+2{{e}^{-}}\xrightarrow{{}}2B{{r}^{-}}E{}^\circ =1.08\,V\] \[E{}^\circ \]values shows\[B{{r}_{2}}\] has higher reduction  potential. Hence \[{{E}_{cell}}={{E}_{R}}-{{E}_{L}}\] \[={{E}_{B{{r}_{2}}/B{{r}^{-}}}}-{{E}_{S{{n}^{+4}}/S{{n}^{+2}}}}\] \[=1.08-0.13=0.95\,V\] Now \[-\Delta G=nF{{E}_{cell}}\] \[n=2,\]\[F=96500\] \[-\Delta G=2\times 96500\times 0.95\,kJ/mol\] Also, \[\Delta G=-2.303\,RT\,\log \,\,{{K}_{eq}}\] \[\log \,\,{{K}_{eq}}=-\frac{\Delta G}{2.303\times R\times T}\] \[=\frac{-(-2\times 96500\times 0.95)}{2.303\times 8.314\times 293}=32.6820\] \[{{K}_{eq}}=\text{antilog}\,\text{32}\text{.682}\] \[=4.78\times {{10}^{32}}\approx {{10}^{32}}\]


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