NEET Chemistry States of Matter / पदार्थ की अवस्थाएँ - गैस एवं द्रव NEET PYQ-States Of Matter

  • question_answer
                 
    For real gases van der Waals' equation is. Written as \[\left( p+\frac{a{{n}^{2}}}{{{V}^{2}}} \right)(V-nb)=n\,RT\] written where, a and b are van der Waals' constants.                                                [AIPMT (M) 2012]
    Two sets of gases are \[I.{{O}_{2}},C{{O}_{2}},{{H}_{2}}\] and He \[II.C{{H}_{4}},{{O}_{2}}\] and \[{{H}_{2}}\]
    The gases given in set-I in increasing order of 'b'  and gases given in set-II in decreasing order of 'a', are arranged below. Select the correct order from the following,              

    A)  \[\text{(I)}\,He\,<\,{{H}_{2}}<\,C{{O}_{2}}<\,{{O}_{2}}\]\[\text{(II})\,C{{H}_{4}}\,>\,{{H}_{2}}>\,{{O}_{2}}\]

    B)  \[\text{(I)}\,\,{{O}_{2}}<\,He\,\,<\,{{H}_{2}}<\,C{{O}_{2}}\]\[\text{(II})\,\,{{H}_{2}}>\,{{O}_{2}}\,\,>\,C{{H}_{4}}\]

    C)  \[\text{(I)}\,\,{{H}_{2}}<\,He\,\,<\,{{O}_{2}}<\,C{{O}_{2}}\]\[\text{(II)}\,C{{H}_{4}}>\,{{O}_{2}}>\,{{H}_{2}}\]

    D)  \[\text{(I)}\,{{H}_{2}}<\,{{O}_{2}}<\,He\,<\,C{{O}_{2}}\]\[\text{(II})\,\,{{O}_{2}}>\,C{{H}_{2}}\,>\,{{H}_{2}}\]

    Correct Answer: C

    Solution :

    From experimental values of and b, sequence of van der Waals’ constant,  is
               
    Gas \[{{H}_{2}}\] \[He\] \[{{O}_{2}}\] \[C{{O}_{2}}\]
    Value of b \[0.0273\] \[0.0318\] \[0.0273\] \[0.0427\]
                Here correct order is
                \[{{H}_{2}}<He<{{O}_{2}}<C{{O}_{2}}\]
                and sequence of van der Waals’ constant  is
               
    Gas \[C{{H}_{4}}\] \[{{O}_{2}}\] \[{{H}_{2}}\]
    Value of b \[2.25\] \[1.36\] \[0.244\]
                            Hence, correct order is
                \[(II)\,\,C{{H}_{4}}>{{O}_{2}}>{{H}_{2}}\]


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