Question

The correct statement during the process of melting of ice or freezing of water is:

• A. Both temperature and internal energy changes
• B. Temperature doesn't change while internal energy changes
• C. Temperature changes while internal energy doesn't change
• D. Cannot be predicted

Answer 1

The correct option is B Temperature doesn't change while internal energy changes

During processes of melting of ice or freezing of water temperature does not change i.e. $dT=0$ but internal energy changes. As $dU=\frac{f}{2}nRdT$ is only valid for ideal gases, so in ideal case only $dU=0$ when $dT=0$.
In real gases there exist intermolecular forces of attraction which is the reason for change in $U$.