Question

Which of the following phenomenon occurs when we open a bottle of perfume and its smell spreads in the entire room within a short time?
  (A) Evaporation
  (B) Sublimation
  (C) Diffusion
  (D) Decantation

Answer 1

Hint: It is a process by which molecules disperse in space in response to differences in concentration. In this phenomenon, the liquid or gaseous molecules travel from the area of higher density to that of the lower density of that substance.


Complete step by step solution:
   - As we all know, when a bottle of perfume is opened in a corner of a room, the scent soon spreads all over the room within a small time. Let's look at the reason why this is happening.
   -According to the kinetic molecular theory, the particles of all substances are in constant motion as long as the temperature is above absolute zero. In solids, the motion of particles is mainly the internal vibration of atoms of the substance, but in the case of liquids and gases, the individual particles can move about.
  - As we are aware, perfume is very volatile. This means that perfume easily changes from a liquid state to gaseous phase at room temperature. When we spray the perfume, the tiny droplets of the liquid are atomized into the air and there they quickly evaporate. Then the gas particles move randomly about, diffusing into the surrounding air in the room, becoming more dilute as they spread out. Within a short span of time, the entire room contains some of the perfume molecules.
    - Thus, the reason for spreading out of perfume is diffusion. The phenomenon diffusion is the tendency of the particles of gas to move from an area of high concentration to an area of low concentration. It can also be explained as the movement of atoms or molecules from a high chemical potential region to a low chemical potential region.
   - When we compare the rate of diffusion in solids, liquids and gases, diffusion is faster in gases than liquid and solid because gas molecules are far apart from each other and their inter-molecular space allows them to accommodate molecules of another gas. This effect is gaseous diffusion.

Therefore, the answer is option (C) Diffusion.


Note: There might be confusion among the options. It should be noted that evaporation happens after the perfume liquid is atomized but this is not the reason for the spreading out of molecules from a higher concentration to a lower one. The phenomenon behind spreading out is diffusion.