Question

The heat of formation of $CO$ and $C{O}_2$ are $-26.4$ kcal and $-94$ kcal respectively. The heat of combustion of carbon monoxide will be:

• A. $+26.4$ kcal
• B. $-67.6$ kcal
• C. $-120.4$ kcal
• D. $+52.8$ kcal

Answer 1

The correct option is B $-67.6$ kcal

We need to calculate heat of combustion of $CO$,
$CO+\frac{1}{2}{O}_2\to C{O}_2$
So, $\Delta H$ = $\Delta H_f^o\left(C{O}_2\right)-\left[\Delta H_f^o\right(CO)+\frac{1}{2}\Delta H_f^o(O_2)$
For elements in pure state $\Delta H_f^o\left(O_2\right)$ = 0
$\Delta H$ = $-94-(-26.4)$ kcal = $-67.6$ kcal