NEET Chemistry Thermodynamics / रासायनिक उष्मागतिकी NEET PYQ-Thermodynamics

  • question_answer
    Which of the following statements is correct for the spontaneous absorption of a gas?               [AIPMT 2014]

    A)  \[\Delta S\] is negative and therefore, \[\Delta H\] should be highly positive

    B)  \[\Delta S\] is negative and therefore, \[\Delta H\] should be highly negative

    C)  \[\Delta S\] is positive and therefore, \[\Delta H\] should be negative

    D)  \[\Delta S\] is positive and therefore, \[\Delta H\] should also be highly positive.

    Correct Answer: B

    Solution :

    \[\Delta S\][change in entropy] and \[\Delta H\] [change in enthalpy] are related by the equation
    \[\Delta G=\Delta H-T\Delta S\]
    [here, \[\Delta G\] = change in Gibbs free energy]
    For adsorption of a gas, \[\Delta S\] is negative because randomness decreases. Thus, in order to make \[\Delta G\] negative [for spontaneous reaction], \[\Delta H\] must be highly negative. Hence, for the adsorption of a gas, if ]\[\Delta S\] is negative, therefore, \[\Delta H\] should be highly negative.


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