Question

$(\Delta H-\Delta U)$ for the formation of carbon monoxide $\left(CO\right)$ from its element at $298K$ is: $(R=8.314J{K}^{-1}{mol}^{-1})$

• A. $-1238.78J{mol}^{-1}$
• B. $1238.78J{mol}^{-1}$
• C. $-2477.57J{mol}^{-1}$
• D. $2477.57J{mol}^{-1}$

Answer 1

The correct option is B $1238.78J{mol}^{-1}$

$C_{\left(S\right)}+\frac{1}{2}{O}_{2\left(g\right)}\to {CO}_{\left(g\right)}$

${\Delta n}_g=1-\frac{1}{2}=0.5$

$\Delta H=\Delta U+{\Delta n}_{g}RT$

$\therefore \Delta H-\Delta U={\Delta n}_g\times R\times T$

$=0.5\times 8.314\times 298$

$\Delta H-\Delta U=1238.78J/mol$