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NEET Chemistry Thermodynamics / रासायनिक उष्मागतिकी Question Bank Self Evaluation Test - Thermodynamics

  • question_answer
    Standard enthalpy of combustion of \[C{{H}_{3}}\] is \[-\,890\text{ }kJ\text{ }mo{{l}^{-1}}\] and standard enthalpy of vaporisation of water is\[40.5\text{ }kJ\text{ }mo{{l}^{-1}}\]. The enthalpy change of the reaction \[C{{H}_{4}}\left( g \right)+2{{O}_{2}}\left( g \right)\xrightarrow{{}}C{{O}_{2}}\left( g \right)+{{H}_{2}}O\left( g \right)\]

    A) \[-809.5\text{ }kJ\text{ }mo{{l}^{-1}}\]            

    B) \[-890\text{ }kJmo{{l}^{-1}}\]

    C) \[809\text{ }kJ\,mo{{l}^{-1}}\]            

    D) \[-971\text{ }kJ\,mo{{l}^{-1}}\]

    Correct Answer: A

    Solution :

    [a] \[C{{H}_{4}}\left( g \right)+2{{O}_{2}}\left( g \right)\xrightarrow{{}}C{{O}_{2}}\left( g \right)+2{{H}_{2}}O\left( l \right)\] \[\Delta H=-890\text{ }kJ\]               .... (i) \[2{{H}_{2}}O\left( l \right)\xrightarrow{{}}2{{H}_{2}}O\left( g \right);\] \[\Delta H=2\times 40.5=81\text{ }kJ\]           .... (ii) From (i) + (ii), we get \[C{{H}_{4}}(g)+2{{O}_{2}}(g)\xrightarrow{{}}C{{O}_{2}}\left( g \right)+2{{H}_{2}}O\left( g \right)\] \[\Delta H=-890+81=-809kJ\]


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