Question

Which of the following statements is correct for the reaction, at constant temperature and pressure?
$CO\left(g\right)+\frac{1}{2}{O}_2\left(g\right)\to {CO}_2\left(g\right)$

• A. $\Delta H=\Delta U$
• B. $\Delta H<\Delta U$
• C. $\Delta H>\Delta U$
• D. None of these

Answer 1

The correct option is B $\Delta H<\Delta U$

Since, $\Delta U=nR\Delta T$
So, at constant temperature $\Delta T=0$
$=>\Delta U=0$
Also, $\Delta H=\Delta U+\left(\Delta n_g\right)RT$, where $\Delta n_g=\text{change in gaseous moles}$
Since, $\Delta n_g=1-1-0.5=-0.5$
So, $\Delta H=0+(-0.5)RT=-0.5RT<0$
Hence, $\Delta H<\Delta U$
Hence, answer is $B$.