Molecular basis for increased water uptake by warm air

2018-06-05 08:20:58

Whats the molecular basis why warm air can uptake more water than cooler air?

It is a common misconception that air “holds” water. Sloppy language describing water vapor mixed with air causes a lot of confusion, but the fact is, the air has nothing to do with it.

In a vessel is a perfect vacuum. You introduce some liquid water. At first, the liquid rapidly boils, but soon it reaches equilibrium—molecules are evaporating and condensing at the same rate. At the bottom of the vessel is liquid water and above it is water vapor. The pressure in the vessel is a function of temperature—at higher temperatures the more energetic liquid molecules have an easier time evaporating, and at equilibrium there are more molecules of vapor.

Now, what happens if you add air to the vessel? Nothing. Now that there are multiple kinds of gas you have to define a “vapor pressure” for each one, with the sum of all the individual vapor pressures equal to the measured pressure. But at any

  • It is a common misconception that air “holds” water. Sloppy language describing water vapor mixed with air causes a lot of confusion, but the fact is, the air has nothing to do with it.

    In a vessel is a perfect vacuum. You introduce some liquid water. At first, the liquid rapidly boils, but soon it reaches equilibrium—molecules are evaporating and condensing at the same rate. At the bottom of the vessel is liquid water and above it is water vapor. The pressure in the vessel is a function of temperature—at higher temperatures the more energetic liquid molecules have an easier time evaporating, and at equilibrium there are more molecules of vapor.

    Now, what happens if you add air to the vessel? Nothing. Now that there are multiple kinds of gas you have to define a “vapor pressure” for each one, with the sum of all the individual vapor pressures equal to the measured pressure. But at any given temperature the equilibrium number of water molecules in the vapor state is the same as i

    2018-06-05 09:01:14