DEMONSTRATION OF RELATION BETWEEN ATOMIC PRESSURE AND BOILING POINT OF A LIQUID:

          A liquid boils when its saturated vapour pressure becomes equal to the external pressure on the liquid. When that happens, it enables bubbles of vapour to form throughout the liquid; those are the bubbles you see when a liquid boils.

If the external pressure is higher than the saturated vapour pressure, these bubbles are prevented from forming, and you just get evaporation at the surface of the liquid.

But at different pressures, water will boil at different temperatures. For example, at the top of Mount Everest the pressure is so low that water will boil at about 70°C. Depressions from the Atlantic can easily lower the atmospheric pressure in the UK enough so that water will boil at 99°C - even lower with very deep depressions.

Whenever we just talk about "the boiling point" of a liquid, we always assume that it is being measured at exactly 1 atmosphere pressure. In practice, of course, that is rarely exactly true.

All liquids, at any temperature, exert a certain vapour pressure. The vapour pressure can be thought of as the degree to which the liquid molecules are escaping into the vapour phase. The vapour pressure increases with temperature, because at higher temperature the molecules are moving faster and more able to overcome the attractive intermolecular forces that tend to bind them together. Boiling occurs when the vapour pressure reaches or exceeds the surrounding pressure from the atmosphere or whatever else is in contact with the liquid.

At standard atmospheric pressure (1 atmosphere, water boils at approximately 100 degrees Celsius. That is simply another way of saying that the vapour pressure of water at that temperature is 1 atmosphere. At higher pressures (such as the pressure generated in a pressure cooker), the temperature must be higher before the vapour pressure reaches the surrounding pressure, so water under pressure boils at a higher temperature. Similarly, when the surrounding pressure is lower (such as at high altitudes), the vapour pressure reaches that pressure at a lower temperature.

What You Need:

• One Round Bottom flask
• Water
• Heating device, e.g. heater
• Handkerchief or paper
• Cork
• Stands

Steps:

• First of all, clean the RB flask and filled it with clean water to half of its volume
• Boil the water in heater.
• Take the flask out of  heater let it be cooled for some time
• Close the opening of flask with cork
• Now, soak the handkerchief in water and put it in the RB flask after the boiling stops to reduce the pressure inside flask, and then observe what happens.
• The water again starts boiling without heating it again at lower temperature than its normal boiling temperature.

Conclusion:

Boiling point of any liquid depends on the pressure at which the liquid is kept. In case of water the boiling point increases with increase in pressure and vice versa.