What type of interaction changes during a phase change?

During a phase change, the interactions that primarily change are hydrogen bonding and Van der Waals forces. These interactions are responsible for the attraction between molecules in various states of matter—solid, liquid, or gas. For instance, when ice melts into water, the rigid hydrogen bonds that keep water molecules in a solid state break and reform as the molecules begin to move more freely as a liquid. Similarly, when water evaporates into steam, the Van der Waals forces that keep the liquid molecules close together are overcome, allowing them to disperse as gas.

Molecular interactions, such as hydrogen bonding and Van der Waals forces, are crucial in understanding these transitions because they can change dramatically without a shift in temperature. For instance, during the melting of ice, the temperature remains constant at 0 degrees Celsius even as energy is added to the system to break those intermolecular attractions, leading to a transformation from solid to liquid.

In contrast, covalent bonds and nuclear interactions remain intact during phase changes. Covalent bonds refer to the strong connections between atoms in a molecule, which do not break during phase changes. Nuclear interactions are confined to the changes within the atomic nuclei and do not play a role in the interactions that lead to phase transitions.