A) + 26.4
B) 120.6
C) -67.6
D) 135.2
Correct Answer: C
Solution :
Given, \[{{\Delta }_{f}}HCO=-26.4\,\text{kcal/mol}\] \[{{\Delta }_{f}}HC{{O}_{2}}=-94.0\,\text{kcal/mol}\] \[CO+\frac{1}{2}{{O}_{2}}\xrightarrow{{}}C{{O}_{2}}\] \[2CO+{{O}_{2}}\xrightarrow{{}}2C{{O}_{2}}\] Heat of combustion, \[{{\Delta }_{r}}H\] \[\sum{{{\Delta }_{f}}H(product)-\sum{{{\Delta }_{f}}H}}(reactants)\] \[=2\times {{\Delta }_{f}}H(C{{O}_{2}})-[2\times {{\Delta }_{f}}H(CO)+{{\Delta }_{f}}H({{O}_{2}})]\] \[=2\times (-94)-[2\times (-26.4)+0]\] \[=-188+52.8=-135.2\] Heat of combustion, \[{{\Delta }_{c}}H=\frac{{{\Delta }_{r}}H}{2}\] \[=\frac{-135.2}{2}=-67.6\,k-\text{cal/mol}\]
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