Question

Give a reason for the following observations :
(A) Naphthalene balls disappear with time without leaving any solid.
(B) We can get the smell of perfumes sitting several meters away.

Answer 1

Hint: Diffusion is the net movement of anything from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in concentration. Sublimation is the transition of a substance directly from the solid to the gas state.

Complete step by step solution: Naphthalene balls disappear with time without leaving any solid. Naphthalene undergoes sublimation easily i.e., the change of state of naphthalene from solid to gas without the intervention of the liquid state. Thus, naphthalene balls keep on forming naphthalene vapours which disappear into the air with time without leaving any solid.
We can get the smell of perfumes sitting several meters away. Perfume has a higher degree of vaporization and its vapour diffuses into the air easily. Gaseous particles possess high speed and move very rapidly in all directions. When perfume is sprayed, its particles diffuse into the particles of air at a very fast rate and reach our nostrils. This enables us to smell the perfume from a distance.
When chemical substances such as perfume are let loose in a room, their particles mix with the particles of air. The particles of smelly gas are free to move quickly in all directions. They eventually spread through the whole room from an area of high concentration to an area of low concentration.

Note: Sublimation is a type of phase transition, or a change in a state of matter, just like melting, freezing, and evaporation. Through sublimation, a substance changes from a solid to a gas without ever passing through a liquid phase. Dry ice, solid CO2, provides a common example of sublimation.