Question

Give a reason to the following observations.
1.Naphthalene balls disappear with time without leaving any solid.
2.We can get the smell of perfumes sitting several meters away.

Answer 1

Hint: Matter exists mainly in three states – liquid, solid, and gas. They have different properties and are interconvertible from one form to another. The gases undergo different types of processes as they can easily flow from one place to another. This leads to a multiple ranges of phenomena observed in certain compounds.

Complete answer:
-Let us talk about observation 1. Matter is divided into 3 states-solid, liquid and gas. All of them are distinguishable from one another and have certain physical and chemical properties.
-Solids are those states of matter which have fixed shape as well as volume. They can be touched and seen by naked eye. The volume of the liquid is fixed but the shape of the liquid is not fixed. The shape of the liquid actually depends on the shape of the container in which they are poured. They can be seen but not touched. Gases neither have fixed shape nor volume. They are invisible to the naked eye.
-All the states of matter are interconvertible. Providing heat to solid converts it to liquid which then converts into gas on further heating. Similarly, if we cool down gases, they convert into liquids and liquids into solids.
     \[solid\overset{\Delta }{\leftrightarrows}liquid\overset{\Delta }{\leftrightarrows}gas\]
-There are certain substances that convert directly into gases from solid state. The process of conversion of matter from solid state directly to gaseous state and vice versa is called sublimation. Some examples of matter that undergo this process are dry ice, moth balls, frozen food, snow in winters.
Thus, naphthalene balls disappear with time without leaving any solid due to sublimation.

-The second observation is: We can get the smell of perfumes sitting several meters away.
This can be explained by the process called DIFFUSION. It can be explained as the process in which a particle moves from the area of higher concentration to an area of lower concentration. It occurs in liquids and gases as they can move freely everywhere as the atoms present in them are very loosely held together and they have the weakest force of attraction.
-Perfumes are liquid in nature. When it is sprayed at a certain area, its concentration is more in that area and less in the adjoining areas. So, by the process of diffusion, it travels from higher concentration region to lower concentration region. The particles randomly in every direction. So, we can smell it sitting several meters away.

Note:
The smell of perfume vanishes after several meters. This is due to the fact that the density of the matter is inversely proportional to the volume of the matter. As the perfume diffuses in the surrounding air, the volume becomes larger and larger and so, the density decreases. Thus, we cannot smell the perfume later on as after a huge distance, the density of surrounding air becomes so large that the density of perfume becomes negligible.