Question

I have read that temperature and pressure dictate how much water vapor can exist in the air.

Air is a mixture, so shouldn’t the addition of water vapor just add to the mixture regardless the temperature and pressure? And since mixture don’t need a specific amount of each of it’s components, why is there a limit even though the atmosphere is so vast?

I have also read that when air is ‘’saturated’’ it means that it reaches the maximum amount of water vapor it can hold at that temperature and pressure

How can water dissolve in air if air is a neutral mixture and water is polar, considering that polar only dissolves polar?

Answer 1

The amount of water vapor the air can contain is determined by the vapor pressure of water, which depends on the temperature and pressure. At equilibrium, the vapor pressure equals the partial pressure of water in the air, and air can't hold more vapor above this point. Water vapor doesn't dissolve in air but exists as a component in the mixture.

Step-by-step explanation:

The air's capacity to hold water vapor is not due to the air actually holding the vapor in a physical sense, but rather is determined by the vapor pressure of water. When water molecules at the surface of a body of water have enough kinetic energy to enter the gas phase, they do so, becoming water vapor. The continual vaporization leads to an increase in pressure, which eventually balances out when an equal number of water molecules condense back into the liquid. The system has then reached equilibrium, and at this point, the vapor pressure is equal to the partial pressure of water vapor present.

At a given temperature, there's a maximum vapor pressure for water above which water will condense. This sets the limit for how much water vapor the air can contain at that particular temperature and pressure. Even though the atmosphere is vast, it's the local temperature and pressure that dictate the maximum concentration of water vapor at any given location. When the air contains the maximum amount of vapor it can at a certain temperature, it's said to be 'saturated', and any additional water added to the system will condense.

Regarding polarity, water vapor does not dissolve in air; rather, it coexists as a separate component within the gaseous mixture.