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CMC Medical CMC-Medical VELLORE Solved Paper-2009

  • question_answer
    Consider following reactions \[I:C(s)+\frac{1}{2}{{O}_{2}}(g)\xrightarrow{{}}CO(g);\,\,\Delta {{H}_{1}}=a\]  \[CO(g)+\frac{1}{2}{{O}_{2}}(g)\xrightarrow{{}}C{{O}_{2}}(g);\,\,\Delta {{H}_{2}}=b\]  \[C(s)+C{{O}_{2}}(g)\xrightarrow{{}}2C{{O}_{2}}(g);\,\,\Delta {{H}_{3}}=c\]Select correct statement

    A)  Heat of formation of \[C{{O}_{2}}\]is (a + b)

    B)  Heat of combustion of\[C\]is (a + b)

    C)  \[\Delta {{H}_{3}}=\Delta {{H}_{1}}-\Delta {{H}_{2}}\]

    D)  All the above are correct statements

    Correct Answer: D

    Solution :

                    I:  \[C(s)+\frac{1}{2}{{O}_{2}}(g)\xrightarrow{{}}CO(g);\]       \[\Delta {{H}_{1}}=a\] II: \[CO(g)+\frac{1}{2}{{O}_{2}}(g)\xrightarrow{{}}C{{O}_{2}}(g);\] \[\Delta {{H}_{2}}=b\] III: \[C(s)+C{{O}_{2}}(g)\xrightarrow{{}}2CO(g);\]   \[\Delta {{H}_{3}}=c\] On adding Eq. I and II, we get \[C(s)+{{O}_{2}}(g)\xrightarrow{{}}C{{O}_{2}}(g);\]\[\Delta H=\Delta {{H}_{1}}+\Delta {{H}_{2}}\]\[=a+b\] \[\therefore \] Heat of formation of \[C{{O}_{2}}=a+b\]and heat of combustion of\[C=a+b\] On subtracting Eq II from I, we get \[C(s)+C{{O}_{2}}(g)\xrightarrow{{}}2CO(g);\] \[\Delta {{H}_{3}}=\Delta {{H}_{1}}-\Delta {{H}_{2}}\]


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