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

  • question_answer
    The standard heat of combustion of Al is \[-\,837.8\,kJ\,mo{{l}^{-1}}\] at \[{{25}^{o}}C\]. If Al reacts with \[{{O}_{2}}\] at \[{{25}^{o}}C,\] which of the following releases 250 kcal of heat?

    A) The reaction of 0.624 mole of Al

    B) The formation of 0.624 mole of \[A{{l}_{2}}{{O}_{3}}\]

    C) The reaction of 0.312 mole of Al

    D) The formation of 0.150 mole of \[A{{l}_{2}}{{O}_{3}}\]

    Correct Answer: B

    Solution :

    [b] \[2\,Al+\frac{3}{2}{{O}_{2}}\xrightarrow{{}}A{{l}_{2}}{{O}_{3}};\]
    \[\Delta {{H}^{o}}=-\,837.8\,kJ\,mo{{l}^{-1}}\]
    2 mol                1.5 mol             1 mol
    1 mol                0.75 mol            0.5 mol
    \[837.8\,kJ\,mo{{l}^{-1}}\equiv \]Combustion of 1 mole Al or formation of 0.5 mole \[A{{l}_{2}}{{O}_{3}}\]
    \[250\,kcal=\frac{250\times 8.314}{2}\,kJ\]
    \[=1.24\,mol\,Al\]
    or         \[=0.62\,mol\] of \[A{{l}_{2}}{{O}_{3}}\]


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