Uttarakhand PMT Uttarakhand PMT Solved Paper-2005

  • question_answer
    The standard e.m.f. for the cell reaction, \[2C{{u}^{2+}}_{(aq)}\xrightarrow[{}]{{}}C{{u}_{(s)}}+C{{u}^{2+}}(aq)\] is +0.36V at 298 K. The equilibrium constant of the reaction is:

    A)  \[5\times {{10}^{6}}\]           

    B)  \[1.4\times {{10}^{12}}\]

    C)  \[7.4\times {{10}^{12}}\]        

    D)  \[1.2\times {{10}^{6}}\]

    Correct Answer: D

    Solution :

     Cell reaction\[2Cu_{(aq)}^{+}\xrightarrow[{}]{{}}C{{u}_{(s)}}+Cu_{(aq)}^{2+}\] According to Nernst equation \[E=E{}^\circ -\frac{2.030RT}{nF}\log \left[ \frac{M}{{{M}^{n+}}} \right]\] \[E=\]Electrode potential of the metal \[E{}^\circ =\]Standard electrode potential \[R=\]gas constant (8.314 joules per mol per degree absolute) \[T=\]Temperature on Kelvin scale \[n=\]Number of electrons involved in the half cell reaction \[F=\]One Faraday (96500 coulombs) at 298 K, 2.303 RT/F = 0.059 \[\therefore \] \[E=E{}^\circ -\frac{0.059}{n}\log \left[ \frac{M}{{{M}^{n+}}} \right]\] \[=E{}^\circ -\frac{0.059}{n}\log \left[ \frac{Products}{Reactants} \right]\] \[E=0\]at equilibrium \[0=E{}^\circ -\frac{0.059}{n}\log {{K}_{eq}}\] Or \[\log {{K}_{eq}}=\frac{nE{}^\circ }{0.059}\] Or \[\log {{K}_{eq}}=\frac{1\times 0.36}{0.059}=6.09\] \[{{K}_{eq}}=1.2\times {{10}^{6}}\]


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