JEE Main & Advanced Chemistry States of Matter / पदार्थ की अवस्थाएँ - गैस एवं द्रव Question Bank Mock Test - States of Matter

  • question_answer
    Total pressure of a mixture of \[{{H}_{2}}\] and \[{{O}_{2}}\] is 1.00 bar. The mixture is allowed to react to form water, which is completely removed to leave only pure \[{{H}_{2}}\] at a pressure of 0.35 bar. Assuming ideal gas behaviour and that all pressure measurements were made under the same temperature and volume conditions, the composition of the original mixture is

    A)
    \[{{X}_{{{H}_{2}}}}\] \[{{X}_{{{O}_{2}}}}\]
    0.50 0.50

    B)
    \[{{X}_{{{H}_{2}}}}\] \[{{X}_{{{O}_{2}}}}\]
    0.22 0.78
     

    C)
    \[{{X}_{{{H}_{2}}}}\] \[{{X}_{{{O}_{2}}}}\]
    0.78 0.22

    D)
    \[{{X}_{{{H}_{2}}}}\] \[{{X}_{{{O}_{2}}}}\]
    0.35 0.65

    Correct Answer: C

    Solution :

    [c] Initially \[{{H}_{2}}\]and \[{{O}_{2}}\]both are present \[pV=nRT\] \[{{n}_{{{H}_{2}}}}+{{n}_{{{o}_{2}}}}={{n}_{(total)}}=\frac{pV}{RT}=\frac{1\times V}{RT}=\frac{V}{RT}\] After reaction is complete, only \[{{H}_{2}}\](unreacted) is left Moles of unreacted \[{{H}_{2}}=\frac{pV}{RT}=\frac{0.35V}{RT}\] Thus, \[n{{'}_{{{H}_{2}}}}+n{{'}_{{{O}_{2}}}}+\]unreacted \[{{H}_{2}}=\frac{V}{RT}\] \[n{{'}_{{{H}_{2}}}}+n{{'}_{{{O}_{2}}}}=\frac{V}{RT}=\frac{0.35V}{RT}\Rightarrow n{{'}_{{{H}_{2}}}}+n{{'}_{{{O}_{2}}}}=\frac{0.65V}{RT}\] Also, \[2{{H}_{2}}(g)+{{O}_{2}}(g)\to 2{{H}_{2}}O(l)\] Moles of \[{{H}_{2}}=2\times \]moles of \[{{O}_{2}}\] \[{{n}_{{{H}_{2}}}}=2n{{}_{{{O}_{2}}}}\] \[\therefore 3{{n}_{{{O}_{2}}}}=\frac{0.65V}{RT};{{n}_{{{O}_{2}}}}=\frac{0.65V}{3RT}\] \[\therefore {{\chi }_{{{O}_{2}}}}=\frac{{{n}_{{{O}_{2}}}}}{{{n}_{total}}}=\frac{0.65V/3RT}{V/RT}=0.22\] \[{{\chi }_{{{H}_{2}}}}=1-0.22=0.78\]


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