Question #14972

1 Answer
Feb 19, 2017

A strong odour might indicate that a large number of molecules are reaching your nose each second, indicating weak interactions among the molecules in the solid.


A substance that evaporates rapidly is said to be volatile. This means that the molecules at the surface of the substance are easily able to leave that surface and escape into the air.

If you think of the forces (bonds) between the molecules that hold them in place in a solid, these forces act like linkages that prevent the molecules from leaving the structure of the solid.

Now, remember that the molecules are in constant motion throughout the solid, and so these bonds are continually being "tested" as the molecules at the surface jostle back and forth.

Occasionally, a molecule will gain enough energy through collisions with its neighbours to break free of the bonding force. This molecule enters the air and eventually may enter your nose, enabling you to smell the solid.

(The solid turning to gas this way is called sublimation. Solid carbon dioxide or "dry ice" is a well known example of this.)

So, the appearance of a strong odour is an indication that many molecules are able to break free of the bonding forces, and that these forces are relatively weak.