Question

$C\left(s\right)+O_2\left(g\right)\to C{O}_2\left(g\right);\Delta H=-94kcal$

$2CO\left(g\right)+O_2\left(g\right)\to 2C{O}_2\left(g\right);\Delta H=-135.2kcal$

The heat of formation of $CO\left(g\right)$ is :

• A. $-26.4kcal$
• B. $41.2kcal$
• C. $26.4kcal$
• D. $229.4kcal$

Answer 1

Answer: (A)

$-26.4kcal$

Given,

$C\left(s\right)+O_2\left(g\right)\to C{O}_2;\Delta H_1=-94Kcal.$ ....(1)

$2CO\left(g\right)+O_2\left(g\right)\to 2C{O}_2\left(g\right);\Delta H_2=-135.2Kcal.$ ....(2)

$\Delta H_f\left(CO\right)=?$

Now the formation of $CO$ is

$C{O}_2\left(g\right)+O_2\left(g\right)\to CO+\frac{1}{2}{O}_2\left(g\right)$ ....(3)

Then, $\Delta H_3=\frac{135.2}{2}=67.6Kcal$

$\therefore$ The required equation,

$C\left(s\right)+\frac{1}{2}{O}_2=CO\left(g\right);\Delta H_4=?$

Adding equation (1) and (3) we get

$C\left(s\right)+\frac{1}{2}{O}_2\to CO\left(g\right)$;

$\Rightarrow \Delta H=-94+67.6=-26.4Kcal$.

$\therefore$ The heat of formation of $CO\left(g\right)$ is $-26.4Kcal$.

Hence, te correct option is $\text{A}$