NEET Sample Paper NEET Sample Test Paper-84

  • question_answer
    Decomposition of \[{{H}_{2}}{{O}_{2}}\] follows a first order reaction. In fifty minutes the concentration of \[{{H}_{2}}{{O}_{2}}\] decreases from 0.5 to 0.125 M in one such decomposition. When the concentration of \[{{H}_{2}}{{O}_{2}}\]reaches 0.05 M, the rate of formation of \[{{O}_{2}}\] will be:

    A) \[2.66\,L\,\,{{\min }^{-1}}\,\text{at}\,\,\text{STP}\]       

    B) \[1.34\times {{10}^{-2\,}}\,\text{mol}\,\,{{\min }^{-1}}\]

    C) \[6.96\times {{10}^{-2}}\,\text{mol}\,\,{{\min }^{-1}}\]

    D) \[6.93\times {{10}^{-4}}\,\text{mol}\,\,{{\min }^{-1}}\]

    Correct Answer: D

    Solution :

    [d] \[{{H}_{2}}{{O}_{2}}(aq)\to {{H}_{2}}O(aq)+\frac{1}{2}{{O}_{2}}(g)\] For a first order reaction             \[k=\frac{2.303}{t}\log \frac{a}{(a-x)}\] Given a\[=0.5,(a-x)=0.125,t=50\,\,\min \] \[\therefore \,\,\,\,\,\,k=\frac{2.303}{50}\log \frac{0.5}{0.125}\] \[=2.78\times {{10}^{-2}}{{\min }^{-1}}\] \[r=k[{{H}_{2}}{{O}_{2}}]=2.78\times {{10}^{-2}}\times 0.05\]                         \[=1.386\times {{10}^{-3}}mol\,\,{{\min }^{-1}}\] Now \[-\frac{d[{{H}_{2}}{{O}_{2}}]}{dt}=\frac{d[{{H}_{2}}O]}{dt}=\frac{2d[{{O}_{2}}]}{dt}\] \[\therefore \]\[\frac{2d[{{O}_{2}}]}{dt}=-\frac{d[{{H}_{2}}{{O}_{2}}]}{dt}\] \[\therefore \]\[\frac{d[{{O}_{2}}]}{dt}=\frac{1}{2}\times \frac{d[{{H}_{2}}{{O}_{2}}]}{dt}\] \[\therefore \]\[\frac{d[{{O}_{2}}]}{dt}=\frac{1}{2}\times \frac{d[{{H}_{2}}{{O}_{2}}]}{dt}\] \[=\frac{1.386\times {{10}^{-3}}}{2}=6.93\times {{10}^{-4}}\,\text{mol}\,\,{{\min }^{-1}}\]


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