# Relationship between barometric pressure and vapor

### What Happens to Air Pressure With an Increase in Water Vapor? | Sciencing

Sure but more often than not, we ignore such influences. Vapor pressure of a liquid is a function of temperature. As can be seen on any phase. Basic Idea: For gaseous bubbles to exist, you need that the pressure inside the bubbles is greater than (or equal) the pressure acting on the. When you talk about air pressure and water vapor, you're talking air evaporates more and faster -- hence the relationship between heat and.

### Pressure and the simple mercury barometer (video) | Khan Academy

And thus the greater the pressure. And if you remember from our last video, we said that temperature was a measure of the average kinetic energy of the particles.

So really what we're saying, is that when we increase the temperature, we're increasing the pressure that the gas exerts. So what else might cause the pressure to increase? Well, if the total pressure is the sum of those little individual collisions, more collisions would mean more pressure.

But how do we increase the number of collisions? One method might be to add more particles, because more particles means more collisions. So more moles of gas- remember that moles is simply referring to the number of particles.

### Vapor pressure - Wikipedia

More moles of gas means more pressure. Now we could also increase the frequency of these collisions by making the container smaller. Because the particles would have less space to move around, and would therefore hit the sides of the container more frequently. So if we decrease the volume- If we decrease the space of the container, we're going to increase the pressure. So we can change the pressure of a gas. But how do we measure those changes?

Well, a long time ago in a former student of Galileo named Evangelista Torricelli asked the same question while he was trying to measure the changing pressure of the gas in our atmosphere.

And he solved the problem by inventing the Torricellian Barometer. A barometer is a device that measures pressure.

And so he took a glass tube, and he filled it up with mercury.

So he took a glass tube and he filled it up with mercury. And he quickly flipped the tube over, and he stuck the open end into an open dish of mercury.

• Does atmospheric pressure affect the vapor pressure of a liquid?
• Basic Idea:

So he stuck the tube into an open dish of mercury, open end down, and interestingly enough, most of the mercury stayed in the tube. And the mercury stayed in the tube, even though it was trying to flow out, because as it tries to flow out it exerts a pressure on the mercury in the dish, which then causes the mercury in the dish to push upward against the air.

## Vapor pressure

And when the pressure of the rising mercury meets the pressure of the atmosphere pushing down on the liquid's surface, the mercury that's in the tube, it can't flow anymore. Shifting Gases The amount of air composed of water vapor is typically 1 to 4 percent.

All gases in the air, including water vapor, exist in constantly shifting proportions.

Saturation, Dewpoint, and Vapor Pressure

Since their total must equal percent, an increase or decrease in the percentage occupied by water vapor results in a decrease or increase of the percentages of other gases. Since atmospheric pressure at sea level is always approximately 1 bar, an increase in water vapor at any given location changes it very little.

At high altitudes overall atmospheric pressure is lower and increases in water vapor have a greater -- though still relatively small -- impact.

Changing Saturation However, there's another "air pressure" measurement that does change significantly with increasing water vapor. This is the saturated vapor pressure, or the proportion of atmospheric pressure attributable to the water vapor itself. The vapor pressure of any substance increases non-linearly with temperature according to the Clausius—Clapeyron relation.

## Pressure and the simple mercury barometer

The atmospheric pressure boiling point of a liquid also known as the normal boiling point is the temperature at which the vapor pressure equals the ambient atmospheric pressure.

With any incremental increase in that temperature, the vapor pressure becomes sufficient to overcome atmospheric pressure and lift the liquid to form vapor bubbles inside the bulk of the substance. Bubble formation deeper in the liquid requires a higher temperature due to the higher fluid pressure, because fluid pressure increases above the atmospheric pressure as the depth increases. More important at shallow depths is the higher temperature required to start bubble formation.

The surface tension of the bubble wall leads to an overpressure in the very small, initial bubbles.