Question

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

• A.
• B.
• C.
• D. None of these

Answer 1

The correct option is B

We know that

$H=U+PV$

$\therefore \Delta H=\Delta U+\Delta PV=\Delta U+P\Delta V+V\Delta P$

At constant pressure we have

$\therefore \Delta H=\Delta U+P\Delta V$

But $P\Delta V=\Delta ngRT$

$\therefore \Delta H=\Delta U+\Delta ngRT$

$\Delta ng$ = number of moles of gaseous products - number of moles of gaseous reactions

$\therefore \Delta ng$ = $1-1-\frac{1}{2}=-\frac{1}{2}$

$\therefore \Delta H=\Delta U-\frac{1}{2}RT$

$\therefore \Delta H+\frac{1}{2}RT=\Delta U$

$\therefore \Delta U>\Delta H$