Chemistry question on pressure.?

Question

Vapor pressure results from molecules in motion as they leave the liquid surface and become vapor. When molecules leave the liquid surface, how is pressure created?

In other words, how is vapor pressure formed? Where does the force come from?

Answer 1

See my answer to your previous question. The force comes from the kinetic energy in the molecules due to heat. Anything above absolute zero will have kinetic energy

Answer 2

It doesnt come from kinetic energy per se.

Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. All solids and liquids have a tendency to evaporate to a gaseous form, and all gases have a tendency to condense back. At any given temperature, for a particular substance, there is a partial pressure at which the gas of that substance is in dynamic equilibrium with its liquid or solid forms. This is the vapor pressure of that substance at that temperature.

example: take a glass bottle and cap it off. Put this bottle in a pot of boiling water. Even after all the water in the pot has boiled off, there will still be water in the capped glass bottle, why? The answer is because of vapor pressure. The pressure is too great for any more liquid molecules to evaporate, and the liquid inside the bottle is at an equilibrium. However, the pressure may become so great that the bottle will shatter, further illustrating vapor pressure.

Conversely, if you take a sample of water and place it in a vacuum, it will simultaneously boil and freeze at the same time. Thus the water will exist in three different forms at the same temperature, due to vapor pressure (or lack thereof in this case).

Answer 3

Hello,
My best guess is that as a liquid is heated, the atoms within it start moving faster, and begin to colide with eachother, and the sides of the container with more force resulting from their higher speeds. The most energetic of these atoms reach velocities (and energies) high enough to escape the liquid and become a gas. Because Pressure in a container is caused by atoms hitting the sides of the container, the atoms with higher velocities (eg. in gas form in this scenario) and therefore higher energies contribute more to the pressure within the container. The hotter it becomes inside the container, the faster the atoms will move, because the higher their energies will be, which means the harder they will hit the sides of the container which will result in a higher pressure within the container. I believe the gas contribution to this pressure is called vapor pressure.
Hope this helped..
Good luck!!

Answer 4

the above is correct

the number of impacts by gas molecules against a surface creates pressure, this is increased by adding more gas molecules, or rasing the temperature (increases kinetic energy) so they move more and thus impact more.