(a) Naphthalene balls disappear over time without leaving a solid residue because they undergo sublimation. Sublimation is the process where a substance transitions directly from a solid state to a gaseous state, bypassing the liquid state. In the case of naphthalene balls, this means they convert directly into naphthalene vapors, which disperse into the air.
Here’s a more detailed explanation:
Sublimation:
Sublimation is a phase transition where a substance changes from a solid to a gas without becoming a liquid. This happens because the molecules in the solid have enough energy to overcome the intermolecular forces holding them in a solid structure, allowing them to directly enter the gaseous state.
Naphthalene’s Sublimation:
Naphthalene, the main component of mothballs, is a solid that readily undergoes sublimation, especially at room temperature. This means that even without any liquid phase, naphthalene molecules can directly transition to a gaseous state.
Disappearance:
When naphthalene balls are left open, the naphthalene molecules in the solid state gain energy and sublimate, turning into naphthalene vapors. These vapors then disperse into the surrounding air, causing the balls to gradually diminish in size and eventually disappear. (b) The ability to smell perfume from a distance is due to diffusion. Perfume particles, being volatile, easily vaporize and spread into the surrounding air, allowing them to travel and be detected by your olfactory senses even from several meters away.
Elaboration:
Volatile Nature of Perfume:
Perfumes contain solvents that are volatile, meaning they evaporate easily due to low boiling points.
Vaporization:
When perfume is sprayed, it vaporizes, turning the liquid into a gas containing the fragrant molecules.
Diffusion:
The perfume vapors, now mixed with air particles, spread out due to the process of diffusion. This means the particles move from an area of high concentration (where the perfume was applied) to an area of lower concentration (the surrounding air).
Detection:
As these perfume particles move through the air, they eventually reach your nostrils, where they interact with olfactory receptors, allowing you to smell the fragrance.
Distance:
The high speed of diffusion and the volatility of the perfume allow these particles to travel significant distances, allowing you to smell the perfume even from a distance.