Identify each of the following changes of state as melting, freezing, sublimation, or deposition: a. Dry ice in an ice-cream cart disappears.

Sublimation is the process in which a solid transitions directly into a gas without passing through the liquid state. This occurs when the molecules in the solid gain enough energy to overcome intermolecular forces, allowing them to escape into the air as gas. A common example is dry ice (solid carbon dioxide), which sublimates at room temperature, creating a fog-like effect.

Phase changes refer to the transitions between different states of matter: solid, liquid, and gas. Each phase change involves energy transfer, which can be in the form of heat. Understanding these changes is crucial for identifying processes like melting (solid to liquid), freezing (liquid to solid), sublimation (solid to gas), and deposition (gas to solid).

Intermolecular forces are the attractive forces between molecules that influence their physical properties and phase changes. In solids, these forces are strong, keeping molecules closely packed, while in gases, they are weak, allowing molecules to move freely. The strength of these forces determines the energy required for a substance to change states, such as during sublimation.