why the boiling point of a liquid varies with pressure
The boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water boils at 100 ° C (212 ° F) at sea level, but at 93.4 ° C (200.1 ° F) at 2,000 metres (6,600 ft) altitude. For a given pressure, different liquids will boil at different temperatures.