Part-2. Effect of external pressure on boiling point | Boiling point | ch#4 | 11th class Chemistry

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In this video I have discussed about the effects of external pressure on boiling point in 11th class Chemistry. i have also discussed about the We have already explained that when vapour pressure of a liquid becomes equal to the
external pressure then the liquid boils, so when external pressure is changed, its boiling point
will also be changed. A liquid can be made to boil at any temperature by changing the external
pressure. When the external pressure is high the liquid requires greater amount of heat to equalize
its vapour pressure to external pressure. In this way boiling point is raised. Similarly, at a lower
external pressure a liquid absorbs less amount of heat and it boils at a lower temperature.
For example, water shows B.P of 120 °C at 1489 torr pressure and boils at 25 °C at 23.7 torr.
Water boils at 98 °C at Murree hills due to external pressure of 700 torr while at the top of Mount
Everest water boils at only 69 0C 323 torr.
We can increase the external pressure artiicially on the surface of boiling water by using a
pressure cooker. Pressure cooker is a closed container. The vapours of water formed are not .allowed to escape. In this way, they develop more pressure in the cooker and the boiling temperature
increases. As more heat is absorbed in water, so food is cooked quickly under increased pressure.
Liquids can be made to boil at low temperatures, where they can be distilled easily. This process
is called vacuum distillation. Vacuum distillation has many advantages. It decreases the time for
the distillation process and is economical because less fuel is required. The decomposition of many
compounds can be avoided e.g. glycerin boils at 290 °C at 760 torr pressure but decomposes at this temperature. Hence, glycerin cannot be distilled at 290 °C. Under vacuum, the boiling temperature
of glycerin decreases to210 0C at 50 torr. It is distilled at this temperature without decomposition and hence can be puriied easily.