Re: [NTLK] OT humidity

From: Mark Ross (markr13_at_comcast.net)
Date: Mon Jul 01 2002 - 20:20:15 EDT


>>>> In the example of water (solute) in air (solvent), the amount maximum
>>>> amount of water that can be held at a given temperature and pressure is
>>>> called 100% relative humidity. It is not possible to hold more than that
>>>> as the air is saturated with water in this state.
>>>
>>> I think that if we want to be truly correct, air is not a solvent and water
>>> is not a solute. Humidity has to do with thermodynamics and phase changes
>>> and isn't really chemistry in the way that term is generally used.
>>>
>>> - Eric.
>>
>> Why not? If water is in a gas state (dissolved) in air, it still obeys
>> the same PV=nRT gas law and will behave much like a solid dissolved in a
>> liquid whereby the solid is now solvated and is liquid-like in behavior.
>> Thermodynamics will play the same role for a liquid-solid solution or two
>> gases. The degree of interaction (thermodynamics) and the temperature
>> (kinetics) will determine what happens at a given P and T.
>>
>>
>
>Because dissolving, IIRC, occurs because water (for example) is a polar
>molecule. That is, the solvent CHEMICALLY aids in some way the dissolving
>of the solute (i.e., by molecular attraction). The N2 and O2 of the
>atmosphere doesn't participate in any such chemical fashion in the
>evaporation of the water. It participates thermodynamically, providing a
>pressure and temperature environment conducive to the maintenance of water
>vapor in the air.
>
>- Eric.

Oxygen is quite polar (and is in the triplet ground state, and therefore
a free radical). To suggest that water and air do not interact is
inaccurate. If water and air were not miscible, they would form separate
layers, just as water and an organic solvent do. Don't get caught in the
trap of looking at things only one way. Laws of thermodynamics, kinetics
and interactions are all intertwined. Nature really doesn't care what
the materials are, their interactions and states are all governed by the
same principles.

Mark Ross
markr13_at_comcast.net

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