Why does the boiling point of a liquid vary at different atmospheric pressures?
at high pressures it is harder to boil a liquid. This is because at high pressure there is more force pushing on the liquid surface (more air above the liquid in a constricted amount of space, means more particles striking the surface of the water, and thus more pressure). This pressure holds the water down and prevents it from becoming airborne vapor. So the water needs more energy (otherwise known as it must be heated to a higher temperature) to become a gas because it must overcome the pressure keeping it down in the water. So in other words. More pressure = more air for the water to push against to get into the air. Less pressure = less air for the water to push against to get into the air part and just to be clear because of the answer below. Boiling is a Physical reaction, it is NOT a chemical reaction.
