Question

The heats of formation of carbon monoxide at constant pressure and at constant volume at ${27}^{o}C$ will differ from one another by:

• A. $27cal$
• B. $54cal$
• C. $300cal$
• D. $600cal$

Answer 1

Answer: (C)

$300cal$

Solution:- (C) $300\text{cal}$

Formation of carbon monoxide-

$C_{\left(s\right)}+\frac{1}{2}{O_2}_{\left(g\right)}⟶{CO}_{\left(g\right)}$

$\Delta n_g=n_P-n_R=1-\frac{1}{2}=\frac{1}{2}$

$T=27℃=(27+273)=300K$

As we know that,

$\Delta H=\Delta U+\Delta n_{g}RT$

$\Rightarrow \Delta H-\Delta U=\Delta n_{g}RT$

$\Rightarrow \Delta H-\Delta U=\frac{1}{2}\times 2\times 300=300\text{cal}$

Hence the heats of formation of carbon monoxide at constant pressure and at constant volume at $27℃$ will differ from one another by $300\text{cal}$.