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AFMC AFMC Solved Paper-2010

  • question_answer
    The heat liberated when 1.89 g of benzoic acid is burnt in a bomb calorimeter at \[25{{\,}^{o}}C\]increases the temperature of 18.94 kg of water by\[~{{0.632}^{o}}C.\] If the specific heat of water at \[{{25}^{o}}C\] is 0.998 cal/g-deg, the value of the heat of combustion of benzoic acid is

    A)  881.1kcal            

    B)  771.4 kcal

    C)  981.1 kcal           

    D)  871.2 kcal

    Correct Answer: B

    Solution :

                     Heat capacity, \[{{C}_{V}}=18.94\times 0.998\times {{10}^{3}}\] \[=18.902\,\times {{10}^{3}}\,cal/\deg \] Moles of benzoic acid \[=\frac{1.89}{1.22}\] \[{{C}_{p}}={{C}_{v}}+R\] \[=18.904\times {{10}^{3}}+2\] \[=18.904\times {{10}^{3}}\,\text{cal}\] Heat of combustion \[=\frac{{{C}_{p}}\times \Delta t}{moles}\]                                 \[=\frac{18.904\times {{10}^{3}}\times 0.632\times 122}{1.89}\] \[=771.2\times {{10}^{3}}\,cal\] \[=771.2\,\text{kcal}\]


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