Question

$2H_2\left(g\right)+O_2\left(g\right)⟶2H_{2}O\left(g\right)$
For this reaction relate $\Delta H$ and $\Delta U$.

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

Answer 1

Answer: (C)

$\Delta H$ < $\Delta U$

As we know,
$\Delta H$ =$\Delta U+\Delta n_{g}RT$
here,
$2H_2\left(g\right)+O_2\left(g\right)⟶2H_{2}O\left(g\right)$
$\Delta n_g=2-1-2=-1$
so,
$\Delta H$ =$\Delta U-RT$
$\Delta H$ < $\Delta U$