Question

Which one the following is a correct relation for the conversion of 1 mole of water into ice:
$H_{2}O\left(l\right)\to H_{2}O\left(s\right)$

• A. $\Delta H>\Delta U$
• B. $\Delta H<\Delta U$
• C. $\Delta H=\Delta U$
• D. none of the above

Answer 1

The correct option is C $\Delta H=\Delta U$

Freezing of water or melting of ice occur at constant temperature and pressure.
We know at constant pressure
$\Delta H=\Delta U+P\Delta V$
there is negligible or almost no change in volume for liquids or solids hence, $\Delta V=0$
so, from above relation $\Delta H=\Delta U$.