Question

Which of the following relationships is not correct for the reaction between $\Delta H$ and $\Delta U$?

• A. When $\Delta n_g$ = 0 then $\Delta H$ = $\Delta U$
• B. When $\Delta n_g$ > 0 then $\Delta H$ > $\Delta U$
• C. When $\Delta n_g$ < 0 then $\Delta H$ < $\Delta U$
• D. When $\Delta n_{g}RT$ = 0 then $\Delta H$ > $\Delta U$

Answer 1

Answer: (D)

When $\Delta n_{g}RT$ = 0 then $\Delta H$ > $\Delta U$

The relation between $\Delta H$ and $\Delta U$ is given as:

$\Delta H=\Delta U+\Delta \left(PV\right)$

i.e., $\Delta H=\Delta U+\Delta n_{g}RT$

$\therefore$ For $\Delta n_g=0,\Delta H=\Delta U$

$\therefore$ For $\Delta n_g>0,\Delta H=\Delta U+\Delta n_{g}RT$

$\therefore$ For $\Delta n_g<0,\Delta H=\Delta U-\Delta n_{g}RT$

$\therefore$ For $\Delta n_{g}RT=0,\Delta H=\Delta U$