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/mol at \[25{}^\circ C\]. Which of the following releases 250 kcal of heat?

    A) The reaction of 0.624 mol of Al

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

    C) The reaction of 0.312 mol of \[Al\]

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

    Correct Answer: B

    Solution :

    [b] \[Al+\frac{3}{4}{{O}_{2}}\xrightarrow{{}}\frac{1}{2}A{{l}_{2}}{{O}_{3}};\,\,\Delta H=-\text{ }837.8\text{ }kJ\]
    Realize energy \[=250\text{ }kcal=250\times 4.2=1050\text{ }kJ\]
    Since 837.8 kJ energy is realized in formation of 0.5 mol \[A{{l}_{2}}{{O}_{3}},\] therefore 1050 kJ energy realized \[\frac{0.5}{837.8}\times 1050=0.624\,mol\]


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