Question

Explain the term - Sublimation. Is sublimation of naphthalene - a physical or a chemical change. Give reasons

Answer 1

Phase transition in a substance refers to a change of state from solid, liquid, or gas to a distinct state. Every element or a substance can undergo transition from one phase to the other phase at a specific temperature and pressure.

Complete step by step answer:
Sublimation is a process in which transformation takes place directly from a solid state to a gas state and vice versa without getting changed into a liquid state. Sublimation is actually a physical change in state and thus, cannot be used to define the transformation of a solid state to a gaseous state in a chemical reaction. For instance, the dissociation of solid ammonium chloride ($N{H_4}Cl$) into hydrogen chloride ($HCl$) and ammonia ($N{H_3}$) is not considered as sublimation but it is a chemical reaction. Sublimation occurs with the absorption of heat that provides sufficient energy for the molecules to counter the attractive forces of their neighbours and help them to escape into the vapour phase. As the sublimation process requires energy, it is considered to be an endothermic process. Examples: Solid carbon dioxide or Dry ice sublimes
Sublimation of naphthalene is a physical change due to the following reasons:
-The chemical composition of naphthalene balls do not alter during the process of sublimation.
-No chemical reaction takes place during the sublimation process.
-Only a change in the physical state occurs which doesn’t mean a chemical change.

Note:
Nilation is also one of the terms stating a change of solid state to gaseous state at above a triple point (temperature and pressure at which three phases coexist) while sublimation occurs below a triple point. Iodine nilates because it can exist as a liquid at atmospheric pressure. Dry ice sublimes because it can’t be a liquid.