Final answer:
Moth balls disappear in a closet through sublimation, the process where a solid turns directly into a vapor without becoming liquid, due to nonzero vapor pressure of solids.
Step-by-step explanation:
Moth balls that disappear after a couple of days in your closet do so by the process known as sublimation. This is when a solid changes directly into a vapor without passing through the liquid phase.
Sublimation occurs because the equilibrium vapor pressure of solids is not zero, which means that at certain temperatures and pressures, molecules in the solid can have enough energy to break away and become a gas. Two common observations that indicate sublimation include the disappearance of dry ice (solid CO2) at room temperature, leaving no liquid residue, and the gradual disappearance of ice cubes in a freezer. Moth balls, made from a substance that sublimates, will also vanish over time as they turn into gas and release their chemicals into the air.