Question

When you remove the lid from a food container that has been left in a freezer for several months, you discover a large collection of ice crystals on the underside of the lid. Explain what has happened.

Answer 1

In the freezer, water may remain frozen, but it has the ability to sublime (change directly from solid phase into vapor phase) slowly that accounts for the so-called freezer burn in improperly wrapped items. This water vapor will undergo deposition (direct change from vapor phase to solid phase, much the same way as snow flakes form in the air, or frost forms on grass and other objects during the night when temperatures fall below the freezing point of water. The same thing happens in a container in the freezer. Water sublimes from the frozen food and deposits itself on the underside of the lid.