Q. Why do mothballs in a closet disappear?

A. If we keep our clothes in a closet for a long period of time, an insect may eat a hole in the fabric, right? When we place mothballs in a closet, the smell coming from the mothball is what to keeps insects away. Since what smells is a gas given off by the mothball, part of the mothball that was originally a solid has escaped as a gas. Consider ice, for example. Ice (a solid) becomes water (a liquid) when the temperature increases and then a vapor (gas) if the temperature rises further. Yet, a mothball never becomes a liquid. That is because a mothball changes from a solid state to a gas directly. We call this change sublimation. It would certainly be a problem if a mothball turned into a liquid and got our clothes wet. That's why substances that sublimate are used for mothballs. Mothballs are primarily made from a petroleum product called para-di-chlorobenzene.