KVPY Sample Paper KVPY Stream-SX Model Paper-10

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

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

    B) \[{{10}^{32}}\]

    C) \[{{10}^{-32}}\]                     

    D) \[{{10}^{-42}}\]

    Correct Answer: B

    Solution :

    \[{{\operatorname{Sn}}^{4}}+2{{e}^{-}}\xrightarrow{{}}S{{n}^{2+}}:E{}^\circ =0.13V\]\[{{\operatorname{Br}}_{2}}+2{{e}^{-}}\xrightarrow{{}}2B{{r}^{-}};E{}^\circ =1.08V\]
    \[\operatorname{E}{}^\circ \]Value shown \[{{\operatorname{Br}}_{2}}\]has higher reduction potential.
    Hence,
    \[{{\operatorname{E}}_{cell}}={{E}_{B{{r}_{2}}/B{{r}^{-}}}}-{{E}_{s{{n}^{+4}}/s{{n}^{+2}}}}\]
        \[=1.08-0.13=0.95V\]
    Now \[-\Delta \operatorname{G}=nF{{E}_{cell}}\]
    \[n=2,\operatorname{F}=96500\]
    \[-\Delta \operatorname{G}=2\times 96500\times 0.95kJ/mol.\]
    Also, \[\Delta \operatorname{G}=-2.303RT\,log\,{{K}_{\operatorname{eq}}}\]
    log \[{{\operatorname{K}}_{\operatorname{eq}}}=antilog32.682\approx {{10}^{32}}\]


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