AMU Medical AMU Solved Paper-2000

  • question_answer
    Which one of the following is the correct decreasing order of boiling point?

    A)  \[{{H}_{2}}Te>{{H}_{2}}O>{{H}_{2}}Se>{{H}_{2}}S\]

    B)                  \[{{H}_{2}}O>{{H}_{2}}S>{{H}_{2}}Se>{{H}_{2}}Te\]

    C)  \[{{H}_{2}}Te>{{H}_{2}}Se>{{H}_{2}}S>{{H}_{2}}O\]

    D)  \[{{H}_{2}}O>{{H}_{2}}Te>{{H}_{2}}Se>{{H}_{2}}S\]

    Correct Answer: D

    Solution :

                     The correct order of boiling point of \[{{H}_{2}}O,\,\,{{H}_{2}}S,\,\,{{H}_{2}}Se\] and \[{{H}_{2}}Te\] is  \[\underset{373\,\,K}{\mathop{{{H}_{2}}O}}\,>\underset{269\,\,K}{\mathop{{{H}_{2}}Te}}\,>\underset{232\,\,K}{\mathop{{{H}_{2}}Se}}\,>\underset{213\,\,K}{\mathop{{{H}_{2}}S}}\,\] The high boiling point of water is due to the association of \[{{H}_{2}}O\] molecules through hydrogen bonding. However, H-bonding is not present in other hydrides. The intermolecular forces between the hydrides (except \[{{H}_{2}}O\]) are van der Waals forces. These forces increase with increase in molecular size and therefore, boiling points increase on moving from \[{{H}_{2}}S\] to \[{{H}_{2}}\]Te.


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