NEET AIPMT SOLVED PAPER SCREENING 2007

  • question_answer
                    The following equilibrium constants are given:                                                                                                   \[{{N}_{2}}+3{{H}_{2}}\,\rightleftharpoons \,2N{{H}_{3}}\,;\,{{K}_{1}}\]                 \[{{N}_{2}}+{{O}_{2}}\,\,\rightleftharpoons \,2NO\,;\,{{K}_{2}}\]                              \[{{H}_{2}}+1/2\,{{O}_{2}}\,\rightleftharpoons \,{{H}_{2}}O\,;\,{{K}_{3}}\]                 The equilibrium constant for the oxidation of \[N{{H}_{3}}\] by oxygen to give NO is:

    A)                 \[{{K}_{2}}K_{3}^{3}/{{K}_{1}}\]               

    B)                 \[{{K}_{2}}\,K_{3}^{2}/{{K}_{1}}\]            

    C)                 \[K_{2}^{2}\,{{K}_{3}}/{{K}_{1}}\]            

    D)                 \[{{K}_{1}}\,{{K}_{2}}/{{K}_{3}}\]

    Correct Answer: A

    Solution :

                    The required equation for the oxidation of NH3 by oxygen to give NO is :                 \[4N{{H}_{3}}+5{{O}_{2}}\underset{{{800}^{o}}C}{\mathop{\xrightarrow{Pt\,(gauze)}}}\,4NO+6{{H}_{2}}O\]                 For this \[K=\frac{{{[NO]}^{4}}\,{{[{{H}_{2}}O]}^{6}}}{{{[N{{H}_{3}}]}^{4}}\,{{[{{O}_{2}}]}^{5}}}\]                 For the equation  \[(I)\,{{K}_{1}}=\frac{{{[N{{H}_{3}}]}^{2}}}{[{{N}_{2}}]\,{{[{{H}_{2}}]}^{3}}}\]                 For the equation \[(II)\,{{K}_{2}}=\frac{{{[NO]}^{2}}}{[{{N}_{2}}]\,[{{O}_{2}}]}\]                 For the equation \[(III)\,{{K}_{3}}=\frac{[{{H}_{2}}O]}{[{{H}_{2}}]\,{{[{{O}_{2}}]}^{1/2}}}\]                 For getting the K we must do   \[K_{1}^{2}=\frac{{{[N{{H}_{3}}]}^{4}}}{{{[{{N}_{2}}]}^{2}}\,{{[{{H}_{2}}]}^{6}}},\,K_{2}^{2}=\frac{{{[NO]}^{4}}}{{{[{{N}_{2}}]}^{2}}\,{{[{{O}_{2}}]}^{2}}}\]                 \[K_{3}^{6}=\frac{{{[{{H}_{2}}O]}^{6}}}{{{[{{H}_{2}}]}^{6}}\,{{[{{O}_{2}}]}^{\frac{6}{2}=3}}}\]                 \[K=\frac{K_{2}^{2}\times K_{3}^{6}}{{{[N{{H}_{3}}]}^{4}}{{[{{O}_{2}}]}^{5}}}\] substituting the value we get,                 \[K=\frac{{{[NO]}^{4}}{{[{{H}_{2}}O]}^{6}}}{{{[N{{H}_{3}}]}^{4}}\,{{[{{O}_{2}}]}^{5}}}\]so the value of K in terms of K1, K2 and K3 is                 \[K=\frac{{{K}_{2}}K_{3}^{3}}{{{K}_{1}}}\]


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