Part-1. Boiling point | ch#4 | 11th class chemistry

#boilingpoint
#boilingpoint11thclasschemistry

in this lecture i have discussed about the boiling point When a liquid is heated, the vapour pressure goes on increasing. A stage reaches when
the vapour pressure of the liquid becomes equal to the external atmospheric pressure. This
temperature is called the boiling point of the liquid. The reason for this is that the bubbles of vapours
which are formed in the interior of the liquid have
greater internal pressure than atmospheric pressure on the surface of liquid. This thing makes the bubble to come out of the liquid and burst upon the surface. Thus a constant stream of bubbles comes out at the boiling point.
When a liquid is heated, the kinetic energy of
its molecules increases and hence the temperature also increases. At the boiling point, the kinetic energy of the molecules becomes maximum and any further heating at this stage will not increase the temperature.Ashows the variation of vapour pressure of water, ethyl alcohol, ethylene glycol
and diethylether with temperature. It shows that the liquids reach upto their boiling points when their vapour pressures are equal to 760 torr at
sea level. The way these curves start at 0
0C is interesting. Water takes start at 4.8
torr while diethyl ether at around 200 torr.
This is due to diference in the strengths
of their intermolecular forces. The curve
for water goes alongwith temperature
axis to a greater extent at the beginning
as compared to ether. It means that water
can hardly overcome its intermolecular
forces at low temperatures. It is clear
from the curves that the vapour pressure
increases very rapidly when the liquids
are closer to their boiling points.