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BCECE Engineering BCECE Engineering Solved Paper-2015

  • question_answer
    Consider the following reactions, \[\text{C(s)+}{{\text{O}}_{\text{2}}}\text{(g)}\to \text{C}{{\text{O}}_{\text{2}}}\text{(g),}\Delta \text{H}=-94\text{kcal}\] \[\text{2CO(g)}+{{\text{O}}_{\text{2}}}\to \text{2C}{{\text{O}}_{\text{2}}}\text{(g),}\Delta \text{H}=-135.2\text{kcal}\] Then, the heat of formation of \[~\text{CO }\left( \text{g} \right)\] is

    A) \[~\text{26}.\text{4 kcal}\]                         

    B) \[-\text{26}.\text{4 kcal}\]

    C) \[~\text{41}.\text{2 kcal}\]                         

    D) \[-\text{41}.\text{2 kcal}\]

    Correct Answer: B

    Solution :

    According to Hess's law, the total heat  changes occuring during a chemical reaction are independent of path. \[2CO(g)+{{O}_{2}}\to 2C{{O}_{2}}(g),\]                                 \[\Delta H=-135.2\text{kcal}\] \[C{{O}_{2}}(g)\to CO+\frac{1}{2}{{O}_{\,}}_{2}(g),\]                                 \[\Delta H=\frac{135.2}{2}\text{kcal}\]   ? (i) \[C+{{O}_{2}}(g)\to C{{O}_{2}}(g),\]                                 \[\Delta H=-94\text{kcal}\]                          ? (ii) Required equation                 \[C(s)+\frac{1}{2}{{O}_{2}}(g)\to CO(g),\Delta H=?\] Adding Eqs. (i) and (ii), we get                               \[\text{C(s)+}\frac{\text{1}}{\text{2}}{{\text{O}}_{\text{2}}}\text{(g)}\to \text{CO(g),    }\!\!\Delta\!\!\text{ H=-26}\text{.4kcal}\]


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