 |
| Picture from study.com |
In order to understand this phenomenon, we should first take a quick review of already known facts:
Boiling Point: It is the temperature at which the Vapor Pressure of the liquid becomes equal to the external Pressure.
Boiling Point is directly related to External Pressure. a. Greater the External Pressure Higher the B.P and vice versa.
Now if we continue to increase the external pressure, the boiling point goes on increasing but up to a certain limit. After that, increasing pressure will not increase the boiling point because the critical temperature has been reached.
Critical Temperature: The maximum temperature at which a substance can exist as liquid or the temperature above which no gas can be liquefied.
There is a Pressure corresponding to critical temperature which is required to bring about the liquefaction of liquid at the critical temperature and is known as Critical Pressure.
Now consider the situation; A substance has a critical temperature of 100 Celsius and corresponding critical pressure value is 1atm (Water), it means that it can exist as a liquid up to 100 Celsius provided the external pressure is 1atm but what if the critical pressure required were 2atm? Obviously the pressure of the air is not enough to liquefy the substance.
Moving further, consider a substance which is present as a solid at room temperature and the critical pressure for the liquid state of this solid substance is above atmospheric pressure. It is easy to understand that the pressure of the atmosphere will not be sufficient to sustain the liquid state of this material due to its lesser quantity as compared to the required value.
What will be the result?
Actually the solid upon melting will not change into the liquid state because the atmospheric pressure is less than the critical pressure and hence it will be directly converted into the vapor phase without pasing through the liquid phase and we will say that the solid is sublime.
Comments
Post a Comment