Vapor pressure + air pressure?

In summary: Dalton's law is not exactly followed by real gases. The deviations are considerably large at high pressures.
  • #1
jmsbot
2
0
Hi, could someone please tell me if the vapor pressure should be combined with the air pressure in a sealed vessel to give the total pressure? For example, if I put room temperature water in a test tube (at sea level) with some head space for air and then seal it, the pressure inside would be 1 bar, would it not? If I then heated the water inside to 100C, the vapor pressure should equal 1 bar also, shouldn't it? Does that mean that the air pressure and the vapor pressure combine to give a total pressure of around 2 bar? Or is the total pressure closer to 1 bar because the air pressure decreases the amount of water that can vaporize at the given temperature? I apologize for my somewhat rudimentary questions and many thanks for your help

James
 
Last edited:
Physics news on Phys.org
  • #3
Thanks, UltrafastPed. So according to Dalton's Law, the partial pressure of the air at 1 bar and the partial pressure of the water vapor at 100C, combine to give a total pressure of 2 bar?

If "Dalton's law is not exactly followed by real gases" and "those deviations are considerably large at high pressures", would 2 bar be considered high enough (for air + water) to cause much of a deviation? Or will it still be relatively close to 2 bar? Thanks again for your help.
 
Last edited:
  • #4
If those are the correct partial pressures, then yes.
 
  • #5
jmsbot said:
Hi, could someone please tell me if the vapor pressure should be combined with the air pressure in a sealed vessel to give the total pressure? For example, if I put room temperature water in a test tube (at sea level) with some head space for air and then seal it, the pressure inside would be 1 bar, would it not?

Yes. Also, as you are in the process of sealing the test tube, the water vapor partial pressure in the head space would attain the equilibrium vapor pressure of water at the test tube temperature, so that the partial pressure of the air in the head space would be slightly less than 1 bar.
If I then heated the water inside to 100C, the vapor pressure should equal 1 bar also, shouldn't it?
Yes.
Does that mean that the air pressure and the vapor pressure combine to give a total pressure of around 2 bar?

Roughly yes. Of course, the air partial pressure would also increase when you heat the test tube, so the total pressure would be greater than 2 bar.
Or is the total pressure closer to 1 bar because the air pressure decreases the amount of water that can vaporize at the given temperature?

No
 

What is vapor pressure?

Vapor pressure is the pressure exerted by a vapor in equilibrium with its condensed phase (liquid or solid) at a given temperature in a closed system.

What is air pressure?

Air pressure, also known as atmospheric pressure, is the force per unit area exerted by the weight of the Earth's atmosphere on the surface of the Earth.

How are vapor pressure and air pressure related?

Vapor pressure and air pressure are related because they both involve the pressure exerted by gases. However, vapor pressure specifically refers to the pressure exerted by a specific vapor, while air pressure refers to the pressure exerted by the Earth's atmosphere as a whole.

How does temperature affect vapor pressure?

As temperature increases, so does vapor pressure. This is because higher temperatures lead to increased kinetic energy of particles, causing more molecules to escape from the liquid or solid phase into the gas phase, resulting in a higher vapor pressure.

How does altitude affect air pressure?

As altitude increases, air pressure decreases. This is because there is less atmosphere above a certain point at higher altitudes, resulting in less weight and therefore less pressure exerted by the atmosphere on that point.

Similar threads

Replies
10
Views
950
Replies
1
Views
926
  • Mechanics
Replies
3
Views
736
Replies
13
Views
3K
Replies
2
Views
711
Replies
40
Views
2K
Replies
3
Views
1K
  • Mechanics
Replies
9
Views
2K
Replies
9
Views
2K
  • Mechanics
Replies
4
Views
2K
Back
Top