JEE Main & Advanced Chemistry Thermodynamics / रासायनिक उष्मागतिकी Sample Paper Topic Test - Thermo Chemistry (Thermodynamics)

  • question_answer
    The heat of hydration of solution anhydrous \[CuS{{O}_{4}}\] and hydrated \[CuS{{O}_{4}}\cdot 5{{H}_{2}}O\] are - 66.5 and 11.7 kJ \[mo{{l}^{-1}}\]respectively. Calculate the heat of hydration of \[CuS{{O}_{4}}\] to \[CuS{{O}_{4}}\cdot 5{{H}_{2}}O\]

    A) - 78.2 kJ

    B) - 81.2 kJ

    C) - 68.2 kJ

    D) - 60.1 kJ

    Correct Answer: A

    Solution :

    [a] The required equation is :
    \[CuS{{O}_{4}}\left( S \right)+5{{H}_{2}}O\left( l \right)\to \]\[CuS{{O}_{4}}.5{{H}_{2}}O\left( s \right)\Delta H=?\]
    given that
    \[CuS{{O}_{4}}.5{{H}_{2}}O\left( S \right)+aq.\to CuS{{O}_{4}}.\left( aq \right);\Delta {{H}_{2}}=+11.7kJ\]
    The process of hydration may be expressed as
    \[\underset{\Delta H}{\mathop{CuS{{O}_{4}}}}\,\left( s \right)\xrightarrow{\Delta {{H}_{1}}}\underset{\Delta {{H}_{2}}}{\mathop{CuS{{O}_{4}}\left( aq \right)}}\,\]\[CuS{{O}_{4}}.5{{H}_{2}}O\]
    According to Hess's law
    \[\Delta {{H}_{1}}=\Delta H+\Delta {{H}_{2}}\]
    \[\Delta {{H}_{1}}=\Delta H-\Delta {{H}_{2}}\]
    \[=-\,66.5-11.7\text{ }=-78.2\text{ }kJ\]

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