Atmospheric Pressure & Boiling Point: Exploring the Why

[PhHsSuga05]

More emphasis...

I understnad that atompsheric pressure affects boiling point and that as atmospheric pressure increases, boiling point increases...but why?

 

[FredGarvin]

Super reduced/no frills version:

Think of a large column of air resting on top of the water trying to boil. In order for the water to be boiling, some of the molecules have to have enough energy to overcome the atmospheric pressure to escape from the water (don't forget a higher pressure will result in a higher density). So a higher pressure would mean a molecule would have to have more energy to break free into the more dense atmosphere, i.e. the water needs a higher temperature. A lower atmospheric pressure means the molecules don't need as much energy.

If you want to start talking about hydrogen bonding and vapor pressure we can. Check out this web site, it may help:http://www.elmhurst.edu/~chm/vchembook/163boilingpt.html

 

[thepatientmental]

The relationship between atmospheric pressure and boiling point can be explained by the concept of vapor pressure. When a liquid is heated, its molecules gain energy and start to move faster. This increased movement causes some molecules to escape the surface of the liquid and enter the gas phase, creating a vapor. The pressure exerted by this vapor is known as vapor pressure.

At a certain temperature, the vapor pressure of a liquid becomes equal to the atmospheric pressure above it. This is known as the boiling point. When the atmospheric pressure is low, the vapor pressure of the liquid is able to overcome it and the liquid boils at a lower temperature. On the other hand, when the atmospheric pressure is high, the vapor pressure needs to be higher to overcome it, resulting in a higher boiling point.

To understand this concept better, let's take the example of water. At sea level, the atmospheric pressure is around 1 bar and the boiling point of water is 100°C. This means that at 100°C, the vapor pressure of water is equal to 1 bar, allowing it to overcome the atmospheric pressure and boil. However, if we were to go to a higher altitude where the atmospheric pressure is lower, let's say 0.5 bar, the boiling point of water would decrease to 90°C. This is because at 90°C, the vapor pressure of water is now equal to 0.5 bar, allowing it to boil at a lower temperature.

Similarly, if we were to increase the atmospheric pressure, let's say to 2 bar, the boiling point of water would increase to 120°C. This is because now the vapor pressure of water needs to be higher, at 2 bar, to overcome the higher atmospheric pressure and boil.

In summary, atmospheric pressure affects boiling point because it determines the vapor pressure needed for a liquid to boil at a certain temperature. As atmospheric pressure increases, the vapor pressure needed also increases, resulting in a higher boiling point. This relationship between atmospheric pressure and boiling point is important in many practical applications, such as cooking and chemical reactions, and understanding it can help us better control and manipulate these processes.